Update version and CHANGELOG.md for v0.21.0

Co-authored-by: Harmen Stoppels <me@harmenstoppels.nl>

.github/workflows/bootstrap.yml

@@ -159,6 +159,9 @@ jobs:
           brew install cmake bison@2.7 tree
       - name: Checkout
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
+      - uses: actions/setup-python@65d7f2d534ac1bc67fcd62888c5f4f3d2cb2b236 # @v2
+        with:
+          python-version: "3.12"
       - name: Bootstrap clingo
         run: |
           source share/spack/setup-env.sh

.github/workflows/build-containers.yml

@@ -38,12 +38,11 @@ jobs:
         # Meaning of the various items in the matrix list
         # 0: Container name (e.g. ubuntu-bionic)
         # 1: Platforms to build for
-        # 2: Base image (e.g. ubuntu:18.04)
+        # 2: Base image (e.g. ubuntu:22.04)
         dockerfile: [[amazon-linux, 'linux/amd64,linux/arm64', 'amazonlinux:2'],
                      [centos7, 'linux/amd64,linux/arm64,linux/ppc64le', 'centos:7'],
                      [centos-stream, 'linux/amd64,linux/arm64,linux/ppc64le', 'centos:stream'],
                      [leap15, 'linux/amd64,linux/arm64,linux/ppc64le', 'opensuse/leap:15'],
-                     [ubuntu-bionic, 'linux/amd64,linux/arm64,linux/ppc64le', 'ubuntu:18.04'],
                      [ubuntu-focal, 'linux/amd64,linux/arm64,linux/ppc64le', 'ubuntu:20.04'],
                      [ubuntu-jammy, 'linux/amd64,linux/arm64,linux/ppc64le', 'ubuntu:22.04'],
                      [almalinux8, 'linux/amd64,linux/arm64,linux/ppc64le', 'almalinux:8'],
@@ -58,18 +57,20 @@ jobs:
       - name: Checkout
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # @v2
 
-      - name: Set Container Tag Normal (Nightly)
-        run: |
-          container="${{ matrix.dockerfile[0] }}:latest"
-          echo "container=${container}" >> $GITHUB_ENV
-          echo "versioned=${container}" >> $GITHUB_ENV
-
-        # On a new release create a container with the same tag as the release.
-      - name: Set Container Tag on Release
-        if: github.event_name == 'release'
-        run: |
-          versioned="${{matrix.dockerfile[0]}}:${GITHUB_REF##*/}"
-          echo "versioned=${versioned}" >> $GITHUB_ENV
+      - uses: docker/metadata-action@96383f45573cb7f253c731d3b3ab81c87ef81934
+        id: docker_meta
+        with:
+          images: |
+              ghcr.io/${{ github.repository_owner }}/${{ matrix.dockerfile[0] }}
+              ${{ github.repository_owner }}/${{ matrix.dockerfile[0] }}
+          tags: |
+              type=schedule,pattern=nightly
+              type=schedule,pattern=develop
+              type=semver,pattern={{version}}
+              type=semver,pattern={{major}}.{{minor}}
+              type=semver,pattern={{major}}
+              type=ref,event=branch
+              type=ref,event=pr
 
       - name: Generate the Dockerfile
         env:
@@ -92,13 +93,13 @@ jobs:
           path: dockerfiles
 
       - name: Set up QEMU
-        uses: docker/setup-qemu-action@68827325e0b33c7199eb31dd4e31fbe9023e06e3 # @v1
+        uses: docker/setup-qemu-action@68827325e0b33c7199eb31dd4e31fbe9023e06e3
 
       - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@f95db51fddba0c2d1ec667646a06c2ce06100226 # @v1
+        uses: docker/setup-buildx-action@f95db51fddba0c2d1ec667646a06c2ce06100226
 
       - name: Log in to GitHub Container Registry
-        uses: docker/login-action@343f7c4344506bcbf9b4de18042ae17996df046d # @v1
+        uses: docker/login-action@343f7c4344506bcbf9b4de18042ae17996df046d
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
@@ -106,21 +107,18 @@ jobs:
 
       - name: Log in to DockerHub
         if: github.event_name != 'pull_request'
-        uses: docker/login-action@343f7c4344506bcbf9b4de18042ae17996df046d # @v1
+        uses: docker/login-action@343f7c4344506bcbf9b4de18042ae17996df046d
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       - name: Build & Deploy ${{ matrix.dockerfile[0] }}
-        uses: docker/build-push-action@0565240e2d4ab88bba5387d719585280857ece09 # @v2
+        uses: docker/build-push-action@0565240e2d4ab88bba5387d719585280857ece09
         with:
           context: dockerfiles/${{ matrix.dockerfile[0] }}
           platforms: ${{ matrix.dockerfile[1] }}
           push: ${{ github.event_name != 'pull_request' }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
-          tags: |
-            spack/${{ env.container }}
-            spack/${{ env.versioned }}
-            ghcr.io/spack/${{ env.container }}
-            ghcr.io/spack/${{ env.versioned }}
+          tags: ${{ steps.docker_meta.outputs.tags }}
+          labels: ${{ steps.docker_meta.outputs.labels }}

.github/workflows/style/requirements.txt

@@ -1,4 +1,4 @@
-black==23.9.1
+black==23.10.1
 clingo==5.6.2
 flake8==6.1.0
 isort==5.12.0

CHANGELOG.md

@@ -1,3 +1,320 @@
+# v0.21.0 (2023-11-11)
+
+`v0.21.0` is a major feature release.
+
+## Features in this release
+
+1. **Better error messages with condition chaining**
+
+   In v0.18, we added better error messages that could tell you what problem happened,
+   but they couldn't tell you *why* it happened. `0.21` adds *condition chaining* to the
+   solver, and Spack can now trace back through the conditions that led to an error and
+   build a tree of causes potential causes and where they came from. For example:
+
+   ```console
+   $ spack solve hdf5 ^cmake@3.0.1
+   ==> Error: concretization failed for the following reasons:
+
+      1. Cannot satisfy 'cmake@3.0.1'
+      2. Cannot satisfy 'cmake@3.0.1'
+           required because hdf5 ^cmake@3.0.1 requested from CLI
+      3. Cannot satisfy 'cmake@3.18:' and 'cmake@3.0.1
+           required because hdf5 ^cmake@3.0.1 requested from CLI
+           required because hdf5 depends on cmake@3.18: when @1.13:
+             required because hdf5 ^cmake@3.0.1 requested from CLI
+      4. Cannot satisfy 'cmake@3.12:' and 'cmake@3.0.1
+           required because hdf5 depends on cmake@3.12:
+             required because hdf5 ^cmake@3.0.1 requested from CLI
+           required because hdf5 ^cmake@3.0.1 requested from CLI
+   ```
+
+   More details in #40173.
+
+2. **OCI build caches**
+
+   You can now use an arbitrary [OCI](https://opencontainers.org) registry as a build
+   cache:
+
+   ```console
+   $ spack mirror add my_registry oci://user/image # Dockerhub
+   $ spack mirror add my_registry oci://ghcr.io/haampie/spack-test # GHCR
+   $ spack mirror set --push --oci-username ... --oci-password ... my_registry  # set login creds
+   $ spack buildcache push my_registry [specs...]
+   ```
+
+   And you can optionally add a base image to get *runnable* images:
+
+   ```console
+   $ spack buildcache push --base-image ubuntu:23.04 my_registry python
+   Pushed ... as [image]:python-3.11.2-65txfcpqbmpawclvtasuog4yzmxwaoia.spack
+
+   $ docker run --rm -it [image]:python-3.11.2-65txfcpqbmpawclvtasuog4yzmxwaoia.spack
+   ```
+
+   This creates a container image from the Spack installations on the host system,
+   without the need to run `spack install` from a `Dockerfile` or `sif` file. It also
+   addresses the inconvenience of losing binaries of dependencies when `RUN spack
+   install` fails inside `docker build`.
+
+   Further, the container image layers and build cache tarballs are the same files. This
+   means that `spack install` and `docker pull` use the exact same underlying binaries.
+   If you previously used `spack install` inside of `docker build`, this feature helps
+   you save storage by a factor two.
+
+   More details in #38358.
+
+3. **Multiple versions of build dependencies**
+
+   Increasingly, complex package builds require multiple versions of some build
+   dependencies. For example, Python packages frequently require very specific versions
+   of `setuptools`, `cython`, and sometimes different physics packages require different
+   versions of Python to build. The concretizer enforced that every solve was *unified*,
+   i.e., that there only be one version of every package. The concretizer now supports
+   "duplicate" nodes for *build dependencies*, but enforces unification through
+   transitive link and run dependencies. This will allow it to better resolve complex
+   dependency graphs in ecosystems like Python, and it also gets us very close to
+   modeling compilers as proper dependencies.
+
+   This change required a major overhaul of the concretizer, as well as a number of
+   performance optimizations. See #38447, #39621.
+
+4. **Cherry-picking virtual dependencies**
+
+   You can now select only a subset of virtual dependencies from a spec that may provide
+   more. For example, if you want `mpich` to be your `mpi` provider, you can be explicit
+   by writing:
+
+   ```
+   hdf5 ^[virtuals=mpi] mpich
+   ```
+
+   Or, if you want to use, e.g., `intel-parallel-studio` for `blas` along with an external
+   `lapack` like `openblas`, you could write:
+
+   ```
+   strumpack ^[virtuals=mpi] intel-parallel-studio+mkl ^[virtuals=lapack] openblas
+   ```
+
+   The `virtuals=mpi` is an edge attribute, and dependency edges in Spack graphs now
+   track which virtuals they satisfied. More details in #17229 and #35322.
+
+   Note for packaging: in Spack 0.21 `spec.satisfies("^virtual")` is true if and only if
+   the package specifies `depends_on("virtual")`. This is different from Spack 0.20,
+   where depending on a provider implied depending on the virtual provided. See #41002
+   for an example where `^mkl` was being used to test for several `mkl` providers in a
+   package that did not depend on `mkl`.
+
+5. **License directive**
+
+   Spack packages can now have license metadata, with the new `license()` directive:
+
+   ```python
+       license("Apache-2.0")
+   ```
+
+   Licenses use [SPDX identifiers](https://spdx.org/licenses), and you can use SPDX
+   expressions to combine them:
+
+   ```python
+       license("Apache-2.0 OR MIT")
+   ```
+
+   Like other directives in Spack, it's conditional, so you can handle complex cases like
+   Spack itself:
+
+   ```python
+      license("LGPL-2.1", when="@:0.11")
+      license("Apache-2.0 OR MIT", when="@0.12:")
+   ```
+
+   More details in #39346, #40598.
+
+6. **`spack deconcretize` command**
+
+   We are getting close to having a `spack update` command for environments, but we're
+   not quite there yet. This is the next best thing. `spack deconcretize` gives you
+   control over what you want to update in an already concrete environment. If you have
+   an environment built with, say, `meson`, and you want to update your `meson` version,
+   you can run:
+
+   ```console
+   spack deconcretize meson
+   ```
+
+   and have everything that depends on `meson` rebuilt the next time you run `spack
+   concretize`. In a future Spack version, we'll handle all of this in a single command,
+   but for now you can use this to drop bits of your lockfile and resolve your
+   dependencies again. More in #38803.
+
+7. **UI Improvements**
+
+   The venerable `spack info` command was looking shabby compared to the rest of Spack's
+   UI, so we reworked it to have a bit more flair. `spack info` now makes much better
+   use of terminal space and shows variants, their values, and their descriptions much
+   more clearly. Conditional variants are grouped separately so you can more easily
+   understand how packages are structured. More in #40998.
+
+   `spack checksum` now allows you to filter versions from your editor, or by version
+   range. It also notifies you about potential download URL changes. See #40403.
+
+8. **Environments can include definitions**
+
+   Spack did not previously support using `include:` with The
+   [definitions](https://spack.readthedocs.io/en/latest/environments.html#spec-list-references)
+   section of an environment, but now it does. You can use this to curate lists of specs
+   and more easily reuse them across environments. See #33960.
+
+9. **Aliases**
+
+   You can now add aliases to Spack commands in `config.yaml`, e.g. this might enshrine
+   your favorite args to `spack find` as `spack f`:
+
+   ```yaml
+   config:
+     aliases:
+       f: find -lv
+   ```
+
+   See #17229.
+
+10. **Improved autoloading of modules**
+
+    Spack 0.20 was the first release to enable autoloading of direct dependencies in
+    module files.
+
+    The downside of this was that `module avail` and `module load` tab completion would
+    show users too many modules to choose from, and many users disabled generating
+    modules for dependencies through `exclude_implicits: true`. Further, it was
+    necessary to keep hashes in module names to avoid file name clashes.
+
+    In this release, you can start using `hide_implicits: true` instead, which exposes
+    only explicitly installed packages to the user, while still autoloading
+    dependencies. On top of that, you can safely use `hash_length: 0`, as this config
+    now only applies to the modules exposed to the user -- you don't have to worry about
+    file name clashes for hidden dependencies.
+
+   Note: for `tcl` this feature requires Modules 4.7 or higher
+
+11. **Updated container labeling**
+
+    Nightly Docker images from the `develop` branch will now be tagged as `:develop` and
+    `:nightly`. The `:latest` tag is no longer associated with `:develop`, but with the
+    latest stable release. Releases will be tagged with `:{major}`, `:{major}.{minor}`
+    and `:{major}.{minor}.{patch}`. `ubuntu:18.04` has also been removed from the list of
+    generated Docker images, as it is no longer supported. See #40593.
+
+## Other new commands and directives
+
+* `spack env activate` without arguments now loads a `default` environment that you do
+  not have to create (#40756).
+* `spack find -H` / `--hashes`: a new shortcut for piping `spack find` output to
+  other commands (#38663)
+* Add `spack checksum --verify`, fix `--add` (#38458)
+* New `default_args` context manager factors out common args for directives (#39964)
+* `spack compiler find --[no]-mixed-toolchain` lets you easily mix `clang` and
+  `gfortran` on Linux (#40902)
+
+## Performance improvements
+
+* `spack external find` execution is now much faster (#39843)
+* `spack location -i` now much faster on success (#40898)
+* Drop redundant rpaths post install (#38976)
+* ASP-based solver: avoid cycles in clingo using hidden directive (#40720)
+* Fix multiple quadratic complexity issues in environments (#38771)
+
+## Other new features of note
+
+* archspec: update to v0.2.2, support for Sapphire Rapids, Power10, Neoverse V2 (#40917)
+* Propagate variants across nodes that don't have that variant (#38512)
+* Implement fish completion (#29549)
+* Can now distinguish between source/binary mirror; don't ping mirror.spack.io as much (#34523)
+* Improve status reporting on install (add [n/total] display) (#37903)
+
+## Windows
+
+This release has the best Windows support of any Spack release yet, with numerous
+improvements and much larger swaths of tests passing:
+
+* MSVC and SDK improvements (#37711, #37930, #38500, #39823, #39180)
+* Windows external finding: update default paths; treat .bat as executable on Windows (#39850)
+* Windows decompression: fix removal of intermediate file (#38958)
+* Windows: executable/path handling (#37762)
+* Windows build systems: use ninja and enable tests (#33589)
+* Windows testing (#36970, #36972, #36973, #36840, #36977, #36792, #36834, #34696, #36971)
+* Windows PowerShell support (#39118, #37951)
+* Windows symlinking and libraries (#39933, #38599, #34701, #38578, #34701)
+
+## Notable refactors
+* User-specified flags take precedence over others in Spack compiler wrappers (#37376)
+* Improve setup of build, run, and test environments (#35737, #40916)
+* `make` is no longer a required system dependency of Spack (#40380)
+* Support Python 3.12 (#40404, #40155, #40153)
+* docs: Replace package list with packages.spack.io (#40251)
+* Drop Python 2 constructs in Spack (#38720, #38718, #38703)
+
+## Binary cache and stack updates
+* e4s arm stack: duplicate and target neoverse v1 (#40369)
+* Add macOS ML CI stacks (#36586)
+* E4S Cray CI Stack (#37837)
+* e4s cray: expand spec list (#38947)
+* e4s cray sles ci: expand spec list (#39081)
+
+## Removals, deprecations, and syntax changes
+* ASP: targets, compilers and providers soft-preferences are only global (#31261)
+* Parser: fix ambiguity with whitespace in version ranges (#40344)
+* Module file generation is disabled by default; you'll need to enable it to use it (#37258)
+* Remove deprecated "extra_instructions" option for containers (#40365)
+* Stand-alone test feature deprecation postponed to v0.22 (#40600)
+* buildcache push: make `--allow-root` the default and deprecate the option (#38878)
+
+## Notable Bugfixes
+* Bugfix: propagation of multivalued variants (#39833)
+* Allow `/` in git versions (#39398)
+* Fetch & patch: actually acquire stage lock, and many more issues (#38903)
+* Environment/depfile: better escaping of targets with Git versions (#37560)
+* Prevent "spack external find" to error out on wrong permissions (#38755)
+* lmod: allow core compiler to be specified with a version range (#37789)
+
+## Spack community stats
+
+* 7,469 total packages, 303 new since `v0.20.0`
+    * 150 new Python packages
+    * 34 new R packages
+* 353 people contributed to this release
+    * 336 committers to packages
+    * 65 committers to core
+
+
+# v0.20.3 (2023-10-31)
+
+## Bugfixes
+
+- Fix a bug where `spack mirror set-url` would drop configured connection info (reverts #34210)
+- Fix a minor issue with package hash computation for Python 3.12 (#40328)
+
+
+# v0.20.2 (2023-10-03)
+
+## Features in this release
+
+Spack now supports Python 3.12 (#40155)
+
+## Bugfixes
+
+- Improve escaping in Tcl module files (#38375)
+- Make repo cache work on repositories with zero mtime (#39214)
+- Ignore errors for newer, incompatible buildcache version (#40279)
+- Print an error when git is required, but missing (#40254)
+- Ensure missing build dependencies get installed when using `spack install --overwrite` (#40252)
+- Fix an issue where Spack freezes when the build process unexpectedly exits (#39015)
+- Fix a bug where installation failures cause an unrelated `NameError` to be thrown (#39017)
+- Fix an issue where Spack package versions would be incorrectly derived from git tags (#39414)
+- Fix a bug triggered when file locking fails internally (#39188)
+- Prevent "spack external find" to error out when a directory cannot be accessed (#38755)
+- Fix multiple performance regressions in environments (#38771)
+- Add more ignored modules to `pyproject.toml` for `mypy` (#38769)
+
+
 # v0.20.1 (2023-07-10)
 
 ## Spack Bugfixes

README.md

@@ -66,7 +66,7 @@ Resources:
 * **Matrix space**: [#spack-space:matrix.org](https://matrix.to/#/#spack-space:matrix.org):
   [bridged](https://github.com/matrix-org/matrix-appservice-slack#matrix-appservice-slack) to Slack.
 * [**Github Discussions**](https://github.com/spack/spack/discussions):
-  not just for discussions, also Q&A.
+  not just for discussions, but also Q&A.
 * **Mailing list**: [groups.google.com/d/forum/spack](https://groups.google.com/d/forum/spack)
 * **Twitter**: [@spackpm](https://twitter.com/spackpm). Be sure to
   `@mention` us!

etc/spack/defaults/config.yaml

@@ -229,3 +229,11 @@ config:
   flags:
     # Whether to keep -Werror flags active in package builds.
     keep_werror: 'none'
+
+  # A mapping of aliases that can be used to define new commands. For instance,
+  # `sp: spec -I` will define a new command `sp` that will execute `spec` with
+  # the `-I` argument. Aliases cannot override existing commands.
+  aliases:
+    concretise: concretize
+    containerise: containerize
+    rm: remove

lib/spack/docs/basic_usage.rst

@@ -1526,6 +1526,30 @@ any MPI implementation will do.  If another package depends on
 error.  Likewise, if you try to plug in some package that doesn't
 provide MPI, Spack will raise an error.
 
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Explicit binding of virtual dependencies
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+There are packages that provide more than just one virtual dependency. When interacting with them, users
+might want to utilize just a subset of what they could provide, and use other providers for virtuals they
+need.
+
+It is possible to be more explicit and tell Spack which dependency should provide which virtual, using a
+special syntax:
+
+.. code-block:: console
+
+   $ spack spec strumpack ^[virtuals=mpi] intel-parallel-studio+mkl ^[virtuals=lapack] openblas
+
+Concretizing the spec above produces the following DAG:
+
+.. figure:: images/strumpack_virtuals.svg
+   :scale: 60 %
+   :align: center
+
+where ``intel-parallel-studio`` *could* provide ``mpi``, ``lapack``, and ``blas`` but is used only for the former. The ``lapack``
+and ``blas`` dependencies are satisfied by ``openblas``.
+
 ^^^^^^^^^^^^^^^^^^^^^^^^
 Specifying Specs by Hash
 ^^^^^^^^^^^^^^^^^^^^^^^^

lib/spack/docs/binary_caches.rst

@@ -155,16 +155,182 @@ List of popular build caches
 
 * `Extreme-scale Scientific Software Stack (E4S) <https://e4s-project.github.io/>`_: `build cache <https://oaciss.uoregon.edu/e4s/inventory.html>`_
 
-
 ----------
 Relocation
 ----------
 
-Initial build and later installation do not necessarily happen at the same
-location. Spack provides a relocation capability and corrects for RPATHs and
-non-relocatable scripts. However, many packages compile paths into binary
-artifacts directly. In such cases, the build instructions of this package would
-need to be adjusted for better re-locatability.
+When using buildcaches across different machines, it is likely that the install
+root will be different from the one used to build the binaries.
+
+To address this issue, Spack automatically relocates all paths encoded in binaries
+and scripts to their new location upon install.
+
+Note that there are some cases where this is not possible: if binaries are built in
+a relatively short path, and then installed to a longer path, there may not be enough
+space in the binary to encode the new path. In this case, Spack will fail to install
+the package from the build cache, and a source build is required.
+
+To reduce the likelihood of this happening, it is highly recommended to add padding to
+the install root during the build, as specified in the :ref:`config <config-yaml>`
+section of the configuration:
+
+.. code-block:: yaml
+
+   config:
+     install_tree:
+       root: /opt/spack
+       padded_length: 128
+
+
+
+-----------------------------------------
+OCI / Docker V2 registries as build cache
+-----------------------------------------
+
+Spack can also use OCI or Docker V2 registries such as Dockerhub, Quay.io,
+Github Packages, GitLab Container Registry, JFrog Artifactory, and others
+as build caches. This is a convenient way to share binaries using public
+infrastructure, or to cache Spack built binaries in Github Actions and
+GitLab CI.
+
+To get started, configure an OCI mirror using ``oci://`` as the scheme,
+and optionally specify a username and password (or personal access token):
+
+.. code-block:: console
+
+    $ spack mirror add --oci-username username --oci-password password my_registry oci://example.com/my_image
+
+Spack follows the naming conventions of Docker, with Dockerhub as the default
+registry. To use Dockerhub, you can omit the registry domain:
+
+.. code-block:: console
+
+    $ spack mirror add --oci-username username --oci-password password my_registry oci://username/my_image
+
+From here, you can use the mirror as any other build cache:
+
+.. code-block:: console
+
+    $ spack buildcache push my_registry <specs...>  # push to the registry
+    $ spack install <specs...> # install from the registry
+
+A unique feature of buildcaches on top of OCI registries is that it's incredibly
+easy to generate get a runnable container image with the binaries installed. This
+is a great way to make applications available to users without requiring them to
+install Spack -- all you need is Docker, Podman or any other OCI-compatible container
+runtime.
+
+To produce container images, all you need to do is add the ``--base-image`` flag
+when pushing to the build cache:
+
+.. code-block:: console
+
+    $ spack buildcache push --base-image ubuntu:20.04 my_registry ninja
+    Pushed to example.com/my_image:ninja-1.11.1-yxferyhmrjkosgta5ei6b4lqf6bxbscz.spack
+
+    $ docker run -it example.com/my_image:ninja-1.11.1-yxferyhmrjkosgta5ei6b4lqf6bxbscz.spack
+    root@e4c2b6f6b3f4:/# ninja --version
+    1.11.1
+
+If ``--base-image`` is not specified, distroless images are produced. In practice,
+you won't be able to run these as containers, since they don't come with libc and
+other system dependencies. However, they are still compatible with tools like
+``skopeo``, ``podman``, and ``docker`` for pulling and pushing.
+
+.. note::
+    The docker ``overlayfs2`` storage driver is limited to 128 layers, above which a
+    ``max depth exceeded`` error may be produced when pulling the image. There
+    are `alternative drivers <https://docs.docker.com/storage/storagedriver/>`_.
+
+------------------------------------
+Spack build cache for GitHub Actions
+------------------------------------
+
+To significantly speed up Spack in GitHub Actions, binaries can be cached in
+GitHub Packages. This service is an OCI registry that can be linked to a GitHub
+repository.
+
+A typical workflow is to include a ``spack.yaml`` environment in your repository
+that specifies the packages to install, the target architecture, and the build
+cache to use under ``mirrors``:
+
+.. code-block:: yaml
+
+    spack:
+      specs:
+      - python@3.11
+      config:
+        install_tree:
+          root: /opt/spack
+          padded_length: 128
+      packages:
+        all:
+          require: target=x86_64_v2
+      mirrors:
+        local-buildcache: oci://ghcr.io/<organization>/<repository>
+
+A GitHub action can then be used to install the packages and push them to the
+build cache:
+
+.. code-block:: yaml
+
+    name: Install Spack packages
+
+    on: push
+
+    env:
+      SPACK_COLOR: always
+
+    jobs:
+      example:
+        runs-on: ubuntu-22.04
+        permissions:
+          packages: write
+        steps:
+        - name: Checkout
+          uses: actions/checkout@v3
+
+        - name: Checkout Spack
+          uses: actions/checkout@v3
+          with:
+            repository: spack/spack
+            path: spack
+
+        - name: Setup Spack
+          run: echo "$PWD/spack/bin" >> "$GITHUB_PATH"
+
+        - name: Concretize
+          run: spack -e . concretize
+
+        - name: Install
+          run: spack -e . install --no-check-signature
+
+        - name: Run tests
+            run: ./my_view/bin/python3 -c 'print("hello world")'
+
+        - name: Push to buildcache
+          run: |
+            spack -e . mirror set --oci-username ${{ github.actor }} --oci-password "${{ secrets.GITHUB_TOKEN }}" local-buildcache
+            spack -e . buildcache push --base-image ubuntu:22.04 --unsigned --update-index local-buildcache
+          if: ${{ !cancelled() }}
+
+The first time this action runs, it will build the packages from source and
+push them to the build cache. Subsequent runs will pull the binaries from the
+build cache. The concretizer will ensure that prebuilt binaries are favored
+over source builds.
+
+The build cache entries appear in the GitHub Packages section of your repository,
+and contain instructions for pulling and running them with ``docker`` or ``podman``.
+
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Using Spack's public build cache for GitHub Actions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Spack offers a public build cache for GitHub Actions with a set of common packages,
+which lets you get started quickly. See the following resources for more information:
+
+* `spack/github-actions-buildcache <https://github.com/spack/github-actions-buildcache>`_
 
 .. _cmd-spack-buildcache:
 

lib/spack/docs/build_settings.rst

@@ -526,56 +526,52 @@ Package Preferences
 In some cases package requirements can be too strong, and package
 preferences are the better option. Package preferences do not impose
 constraints on packages for particular versions or variants values,
-they rather only set defaults -- the concretizer is free to change
-them if it must due to other constraints. Also note that package
-preferences are of lower priority than reuse of already installed
-packages.
+they rather only set defaults. The concretizer is free to change
+them if it must, due to other constraints, and also prefers reusing
+installed packages over building new ones that are a better match for
+preferences.
 
-Here's an example ``packages.yaml`` file that sets preferred packages:
+Most package preferences (``compilers``, ``target`` and ``providers``)
+can only be set globally under the ``all`` section of ``packages.yaml``:
+
+.. code-block:: yaml
+
+   packages:
+     all:
+       compiler: [gcc@12.2.0, clang@12:, oneapi@2023:]
+       target: [x86_64_v3]
+       providers:
+         mpi: [mvapich2, mpich, openmpi]
+
+These preferences override Spack's default and effectively reorder priorities
+when looking for the best compiler, target or virtual package provider. Each
+preference takes an ordered list of spec constraints, with earlier entries in
+the list being preferred over later entries.
+
+In the example above all packages prefer to be compiled with ``gcc@12.2.0``,
+to target the ``x86_64_v3`` microarchitecture and to use ``mvapich2`` if they
+depend on ``mpi``.
+
+The ``variants`` and ``version`` preferences can be set under
+package specific sections of the ``packages.yaml`` file:
 
 .. code-block:: yaml
 
    packages:
      opencv:
-       compiler: [gcc@4.9]
        variants: +debug
      gperftools:
        version: [2.2, 2.4, 2.3]
-     all:
-       compiler: [gcc@4.4.7, 'gcc@4.6:', intel, clang, pgi]
-       target: [sandybridge]
-       providers:
-         mpi: [mvapich2, mpich, openmpi]
 
-At a high level, this example is specifying how packages are preferably
-concretized.  The opencv package should prefer using GCC 4.9 and
-be built with debug options.  The gperftools package should prefer version
-2.2 over 2.4.  Every package on the system should prefer mvapich2 for
-its MPI and GCC 4.4.7 (except for opencv, which overrides this by preferring GCC 4.9).
-These options are used to fill in implicit defaults.  Any of them can be overwritten
-on the command line if explicitly requested.
+In this case, the preference for ``opencv`` is to build with debug options, while
+``gperftools`` prefers version 2.2 over 2.4.
 
-Package preferences accept the follow keys or components under
-the specific package (or ``all``) section: ``compiler``, ``variants``,
-``version``, ``providers``, and ``target``.  Each component has an
-ordered list of spec ``constraints``, with earlier entries in the
-list being preferred over later entries.
+Any preference can be overwritten on the command line if explicitly requested.
 
-Sometimes a package installation may have constraints that forbid
-the first concretization rule, in which case Spack will use the first
-legal concretization rule.  Going back to the example, if a user
-requests gperftools 2.3 or later, then Spack will install version 2.4
-as the 2.4 version of gperftools is preferred over 2.3.
-
-An explicit concretization rule in the preferred section will always
-take preference over unlisted concretizations.  In the above example,
-xlc isn't listed in the compiler list.  Every listed compiler from
-gcc to pgi will thus be preferred over the xlc compiler.
-
-The syntax for the ``provider`` section differs slightly from other
-concretization rules.  A provider lists a value that packages may
-``depends_on`` (e.g, MPI) and a list of rules for fulfilling that
-dependency.
+Preferences cannot overcome explicit constraints, as they only set a preferred
+ordering among homogeneous attribute values. Going back to the example, if
+``gperftools@2.3:`` was requested, then Spack will install version 2.4
+since the most preferred version 2.2 is prohibited by the version constraint.
 
 .. _package_permissions:
 

lib/spack/docs/build_systems/autotoolspackage.rst

@@ -127,9 +127,9 @@ check out a commit from the ``master`` branch, you would want to add:
 
 .. code-block:: python
 
-   depends_on('autoconf', type='build', when='@master')
-   depends_on('automake', type='build', when='@master')
-   depends_on('libtool',  type='build', when='@master')
+   depends_on("autoconf", type="build", when="@master")
+   depends_on("automake", type="build", when="@master")
+   depends_on("libtool",  type="build", when="@master")
 
 It is typically redundant to list the ``m4`` macro processor package as a
 dependency, since ``autoconf`` already depends on it.
@@ -145,7 +145,7 @@ example, the ``bash`` shell is used to run the ``autogen.sh`` script.
 .. code-block:: python
 
    def autoreconf(self, spec, prefix):
-       which('bash')('autogen.sh')
+       which("bash")("autogen.sh")
 
 """""""""""""""""""""""""""""""""""""""
 patching configure or Makefile.in files
@@ -186,9 +186,9 @@ To opt out of this feature, use the following setting:
 To enable it conditionally on different architectures, define a property and
 make the package depend on ``gnuconfig`` as a build dependency:
 
-.. code-block
+.. code-block:: python
 
-   depends_on('gnuconfig', when='@1.0:')
+   depends_on("gnuconfig", when="@1.0:")
 
    @property
    def patch_config_files(self):
@@ -230,7 +230,7 @@ version, this can be done like so:
 
    @property
    def force_autoreconf(self):
-       return self.version == Version('1.2.3')
+       return self.version == Version("1.2.3")
 
 ^^^^^^^^^^^^^^^^^^^^^^^
 Finding configure flags
@@ -278,13 +278,22 @@ function like so:
    def configure_args(self):
        args = []
 
-       if '+mpi' in self.spec:
-           args.append('--enable-mpi')
+       if self.spec.satisfies("+mpi"):
+           args.append("--enable-mpi")
        else:
-           args.append('--disable-mpi')
+           args.append("--disable-mpi")
 
        return args
 
+
+Alternatively, you can use the :ref:`enable_or_disable  <autotools_enable_or_disable>` helper:
+
+.. code-block:: python
+
+   def configure_args(self):
+       return [self.enable_or_disable("mpi")]
+
+
 Note that we are explicitly disabling MPI support if it is not
 requested. This is important, as many Autotools packages will enable
 options by default if the dependencies are found, and disable them
@@ -295,9 +304,11 @@ and `here <https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Automagic_depe
 for a rationale as to why these so-called "automagic" dependencies
 are a problem.
 
-By default, Autotools installs packages to ``/usr``. We don't want this,
-so Spack automatically adds ``--prefix=/path/to/installation/prefix``
-to your list of ``configure_args``. You don't need to add this yourself.
+.. note::
+
+   By default, Autotools installs packages to ``/usr``. We don't want this,
+   so Spack automatically adds ``--prefix=/path/to/installation/prefix``
+   to your list of ``configure_args``. You don't need to add this yourself.
 
 ^^^^^^^^^^^^^^^^
 Helper functions
@@ -308,6 +319,8 @@ You may have noticed that most of the Autotools flags are of the form
 ``--without-baz``. Since these flags are so common, Spack provides a
 couple of helper functions to make your life easier.
 
+.. _autotools_enable_or_disable:
+
 """""""""""""""""
 enable_or_disable
 """""""""""""""""
@@ -319,11 +332,11 @@ typically used to enable or disable some feature within the package.
 .. code-block:: python
 
    variant(
-       'memchecker',
+       "memchecker",
        default=False,
-       description='Memchecker support for debugging [degrades performance]'
+       description="Memchecker support for debugging [degrades performance]"
    )
-   config_args.extend(self.enable_or_disable('memchecker'))
+   config_args.extend(self.enable_or_disable("memchecker"))
 
 In this example, specifying the variant ``+memchecker`` will generate
 the following configuration options:
@@ -343,15 +356,15 @@ the ``with_or_without`` method.
 .. code-block:: python
 
    variant(
-       'schedulers',
+       "schedulers",
        values=disjoint_sets(
-           ('auto',), ('alps', 'lsf', 'tm', 'slurm', 'sge', 'loadleveler')
-       ).with_non_feature_values('auto', 'none'),
+           ("auto",), ("alps", "lsf", "tm", "slurm", "sge", "loadleveler")
+       ).with_non_feature_values("auto", "none"),
        description="List of schedulers for which support is enabled; "
        "'auto' lets openmpi determine",
    )
-   if 'schedulers=auto' not in spec:
-       config_args.extend(self.with_or_without('schedulers'))
+   if not spec.satisfies("schedulers=auto"):
+       config_args.extend(self.with_or_without("schedulers"))
 
 In this example, specifying the variant ``schedulers=slurm,sge`` will
 generate the following configuration options:
@@ -376,16 +389,16 @@ generated, using the ``activation_value`` argument to
 .. code-block:: python
 
    variant(
-      'fabrics',
+      "fabrics",
        values=disjoint_sets(
-           ('auto',), ('psm', 'psm2', 'verbs', 'mxm', 'ucx', 'libfabric')
-       ).with_non_feature_values('auto', 'none'),
+           ("auto",), ("psm", "psm2", "verbs", "mxm", "ucx", "libfabric")
+       ).with_non_feature_values("auto", "none"),
        description="List of fabrics that are enabled; "
        "'auto' lets openmpi determine",
    )
-   if 'fabrics=auto' not in spec:
-       config_args.extend(self.with_or_without('fabrics',
-           activation_value='prefix'))
+   if not spec.satisfies("fabrics=auto"):
+       config_args.extend(self.with_or_without("fabrics",
+           activation_value="prefix"))
 
 ``activation_value`` accepts a callable that generates the configure
 parameter value given the variant value; but the special value
@@ -409,16 +422,16 @@ When Spack variants and configure flags do not correspond one-to-one, the
 
 .. code-block:: python
 
-   variant('debug_tools', default=False)
-   config_args += self.enable_or_disable('debug-tools', variant='debug_tools')
+   variant("debug_tools", default=False)
+   config_args += self.enable_or_disable("debug-tools", variant="debug_tools")
 
 Or when one variant controls multiple flags:
 
 .. code-block:: python
 
-   variant('debug_tools', default=False)
-   config_args += self.with_or_without('memchecker', variant='debug_tools')
-   config_args += self.with_or_without('profiler', variant='debug_tools')
+   variant("debug_tools", default=False)
+   config_args += self.with_or_without("memchecker", variant="debug_tools")
+   config_args += self.with_or_without("profiler", variant="debug_tools")
 
 
 """"""""""""""""""""
@@ -432,8 +445,8 @@ For example:
 
 .. code-block:: python
 
-   variant('profiler', when='@2.0:')
-   config_args += self.with_or_without('profiler')
+   variant("profiler", when="@2.0:")
+   config_args += self.with_or_without("profiler")
 
 will neither add ``--with-profiler`` nor ``--without-profiler`` when the version is
 below ``2.0``.
@@ -452,10 +465,10 @@ the variant values require atypical behavior.
    def with_or_without_verbs(self, activated):
        # Up through version 1.6, this option was named --with-openib.
        # In version 1.7, it was renamed to be --with-verbs.
-       opt = 'verbs' if self.spec.satisfies('@1.7:') else 'openib'
+       opt = "verbs" if self.spec.satisfies("@1.7:") else "openib"
        if not activated:
-           return '--without-{0}'.format(opt)
-       return '--with-{0}={1}'.format(opt, self.spec['rdma-core'].prefix)
+           return f"--without-{opt}"
+       return f"--with-{opt}={self.spec['rdma-core'].prefix}"
 
 Defining ``with_or_without_verbs`` overrides the behavior of a
 ``fabrics=verbs`` variant, changing the configure-time option to
@@ -479,7 +492,7 @@ do this like so:
 
 .. code-block:: python
 
-   configure_directory = 'src'
+   configure_directory = "src"
 
 ^^^^^^^^^^^^^^^^^^^^^^
 Building out of source
@@ -491,7 +504,7 @@ This can be done using the ``build_directory`` variable:
 
 .. code-block:: python
 
-   build_directory = 'spack-build'
+   build_directory = "spack-build"
 
 By default, Spack will build the package in the same directory that
 contains the ``configure`` script
@@ -514,8 +527,8 @@ library or build the documentation, you can add these like so:
 
 .. code-block:: python
 
-   build_targets = ['all', 'docs']
-   install_targets = ['install', 'docs']
+   build_targets = ["all", "docs"]
+   install_targets = ["install", "docs"]
 
 ^^^^^^^
 Testing

lib/spack/docs/build_systems/cachedcmakepackage.rst

@@ -87,7 +87,7 @@ A typical usage of these methods may look something like this:
 
 .. code-block:: python
 
-   def initconfig_mpi_entries(self)
+   def initconfig_mpi_entries(self):
        # Get existing MPI configurations
        entries = super(self, Foo).initconfig_mpi_entries()
 
@@ -95,25 +95,25 @@ A typical usage of these methods may look something like this:
        # This spec has an MPI variant, and we need to enable MPI when it is on.
        # This hypothetical package controls MPI with the ``FOO_MPI`` option to
        # cmake.
-       if '+mpi' in self.spec:
-           entries.append(cmake_cache_option('FOO_MPI', True, "enable mpi"))
+       if self.spec.satisfies("+mpi"):
+           entries.append(cmake_cache_option("FOO_MPI", True, "enable mpi"))
        else:
-           entries.append(cmake_cache_option('FOO_MPI', False, "disable mpi"))
+           entries.append(cmake_cache_option("FOO_MPI", False, "disable mpi"))
 
    def initconfig_package_entries(self):
        # Package specific options
        entries = []
 
-       entries.append('#Entries for build options')
+       entries.append("#Entries for build options")
 
-       bar_on = '+bar' in self.spec
-       entries.append(cmake_cache_option('FOO_BAR', bar_on, 'toggle bar'))
+       bar_on = self.spec.satisfies("+bar")
+       entries.append(cmake_cache_option("FOO_BAR", bar_on, "toggle bar"))
 
-       entries.append('#Entries for dependencies')
+       entries.append("#Entries for dependencies")
 
-       if self.spec['blas'].name == 'baz':  # baz is our blas provider
-       entries.append(cmake_cache_string('FOO_BLAS', 'baz', 'Use baz'))
-       entries.append(cmake_cache_path('BAZ_PREFIX', self.spec['baz'].prefix))
+       if self.spec["blas"].name == "baz":  # baz is our blas provider
+           entries.append(cmake_cache_string("FOO_BLAS", "baz", "Use baz"))
+           entries.append(cmake_cache_path("BAZ_PREFIX", self.spec["baz"].prefix))
 
 ^^^^^^^^^^^^^^^^^^^^^^
 External documentation

lib/spack/docs/build_systems/cudapackage.rst

@@ -54,8 +54,8 @@ to terminate such build attempts with a suitable message:
 
 .. code-block:: python
 
-    conflicts('cuda_arch=none', when='+cuda',
-              msg='CUDA architecture is required')
+    conflicts("cuda_arch=none", when="+cuda",
+              msg="CUDA architecture is required")
 
 Similarly, if your software does not support all versions of the property,
 you could add ``conflicts`` to your package for those versions.  For example,
@@ -66,13 +66,13 @@ custom message should a user attempt such a build:
 .. code-block:: python
 
     unsupported_cuda_archs = [
-        '10', '11', '12', '13',
-        '20', '21',
-        '30', '32', '35', '37'
+        "10", "11", "12", "13",
+        "20", "21",
+        "30", "32", "35", "37"
     ]
     for value in unsupported_cuda_archs:
-        conflicts('cuda_arch={0}'.format(value), when='+cuda',
-                  msg='CUDA architecture {0} is not supported'.format(value))
+        conflicts(f"cuda_arch={value}", when="+cuda",
+                  msg=f"CUDA architecture {value} is not supported")
 
 ^^^^^^^
 Methods
@@ -107,16 +107,16 @@ class of your package.  For example, you can add it to your
             spec = self.spec
             args = []
             ...
-            if '+cuda' in spec:
+            if spec.satisfies("+cuda"):
                 # Set up the cuda macros needed by the build
-                args.append('-DWITH_CUDA=ON')
-                cuda_arch_list = spec.variants['cuda_arch'].value
+                args.append("-DWITH_CUDA=ON")
+                cuda_arch_list = spec.variants["cuda_arch"].value
                 cuda_arch = cuda_arch_list[0]
-                if cuda_arch != 'none':
-                    args.append('-DCUDA_FLAGS=-arch=sm_{0}'.format(cuda_arch))
+                if cuda_arch != "none":
+                    args.append(f"-DCUDA_FLAGS=-arch=sm_{cuda_arch}")
             else:
                 # Ensure build with cuda is disabled
-                args.append('-DWITH_CUDA=OFF')
+                args.append("-DWITH_CUDA=OFF")
             ...
             return args
 
@@ -125,7 +125,7 @@ You will need to customize options as needed for your build.
 
 This example also illustrates how to check for the ``cuda`` variant using
 ``self.spec`` and how to retrieve the ``cuda_arch`` variant's value, which
-is a list, using ``self.spec.variants['cuda_arch'].value``.
+is a list, using ``self.spec.variants["cuda_arch"].value``.
 
 With over 70 packages using ``CudaPackage`` as of January 2021 there are
 lots of examples to choose from to get more ideas for using this package.

lib/spack/docs/build_systems/custompackage.rst

@@ -57,13 +57,13 @@ If you look at the ``perl`` package, you'll see:
 
 .. code-block:: python
 
-   phases = ['configure', 'build', 'install']
+   phases = ["configure", "build", "install"]
 
 Similarly, ``cmake`` defines:
 
 .. code-block:: python
 
-   phases = ['bootstrap', 'build', 'install']
+   phases = ["bootstrap", "build", "install"]
 
 If we look at the ``cmake`` example, this tells Spack's ``PackageBase``
 class to run the ``bootstrap``, ``build``, and ``install`` functions
@@ -78,7 +78,7 @@ If we look at ``perl``, we see that it defines a ``configure`` method:
 .. code-block:: python
 
    def configure(self, spec, prefix):
-       configure = Executable('./Configure')
+       configure = Executable("./Configure")
        configure(*self.configure_args())
 
 There is also a corresponding ``configure_args`` function that handles
@@ -92,7 +92,7 @@ phases are pretty simple:
        make()
 
    def install(self, spec, prefix):
-       make('install')
+       make("install")
 
 The ``cmake`` package looks very similar, but with a ``bootstrap``
 function instead of ``configure``:
@@ -100,14 +100,14 @@ function instead of ``configure``:
 .. code-block:: python
 
    def bootstrap(self, spec, prefix):
-       bootstrap = Executable('./bootstrap')
+       bootstrap = Executable("./bootstrap")
        bootstrap(*self.bootstrap_args())
 
    def build(self, spec, prefix):
        make()
 
    def install(self, spec, prefix):
-       make('install')
+       make("install")
 
 Again, there is a ``boostrap_args`` function that determines the
 correct bootstrap flags to use.
@@ -128,16 +128,16 @@ before or after a particular phase. For example, in ``perl``, we see:
 
 .. code-block:: python
 
-   @run_after('install')
+   @run_after("install")
    def install_cpanm(self):
        spec = self.spec
 
-       if '+cpanm' in spec:
-           with working_dir(join_path('cpanm', 'cpanm')):
-               perl = spec['perl'].command
-               perl('Makefile.PL')
+       if spec.satisfies("+cpanm"):
+           with working_dir(join_path("cpanm", "cpanm")):
+               perl = spec["perl"].command
+               perl("Makefile.PL")
                make()
-               make('install')
+               make("install")
 
 This extra step automatically installs ``cpanm`` in addition to the
 base Perl installation.
@@ -174,10 +174,10 @@ In the ``perl`` package, we can see:
 
 .. code-block:: python
 
-   @run_after('build')
+   @run_after("build")
    @on_package_attributes(run_tests=True)
    def test(self):
-       make('test')
+       make("test")
 
 As you can guess, this runs ``make test`` *after* building the package,
 if and only if testing is requested. Again, this is not specific to
@@ -189,7 +189,7 @@ custom build systems, it can be added to existing build systems as well.
 
    .. code-block:: python
 
-      @run_after('install')
+      @run_after("install")
       @on_package_attributes(run_tests=True)
 
    works as expected. However, if you reverse the ordering:
@@ -197,7 +197,7 @@ custom build systems, it can be added to existing build systems as well.
    .. code-block:: python
 
       @on_package_attributes(run_tests=True)
-      @run_after('install')
+      @run_after("install")
 
    the tests will always be run regardless of whether or not
    ``--test=root`` is requested. See https://github.com/spack/spack/issues/3833

lib/spack/docs/build_systems/makefilepackage.rst

@@ -59,7 +59,7 @@ using GNU Make, you should add a dependency on ``gmake``:
 
 .. code-block:: python
 
-   depends_on('gmake', type='build')
+   depends_on("gmake", type="build")
 
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -93,8 +93,8 @@ there are any other variables you need to set, you can do this in the
 .. code-block:: python
 
    def edit(self, spec, prefix):
-       env['PREFIX'] = prefix
-       env['BLASLIB'] = spec['blas'].libs.ld_flags
+       env["PREFIX"] = prefix
+       env["BLASLIB"] = spec["blas"].libs.ld_flags
 
 
 `cbench <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/cbench/package.py>`_
@@ -113,7 +113,7 @@ you can do this like so:
 
 .. code-block:: python
 
-   build_targets = ['CC=cc']
+   build_targets = ["CC=cc"]
 
 
 If you do need access to the spec, you can create a property like so:
@@ -125,8 +125,8 @@ If you do need access to the spec, you can create a property like so:
        spec = self.spec
 
        return [
-           'CC=cc',
-           'BLASLIB={0}'.format(spec['blas'].libs.ld_flags),
+           "CC=cc",
+           f"BLASLIB={spec['blas'].libs.ld_flags}",
        ]
 
 
@@ -145,12 +145,12 @@ and a ``filter_file`` method to help with this. For example:
 .. code-block:: python
 
    def edit(self, spec, prefix):
-       makefile = FileFilter('Makefile')
+       makefile = FileFilter("Makefile")
 
-       makefile.filter(r'^\s*CC\s*=.*',  'CC = '  + spack_cc)
-       makefile.filter(r'^\s*CXX\s*=.*', 'CXX = ' + spack_cxx)
-       makefile.filter(r'^\s*F77\s*=.*', 'F77 = ' + spack_f77)
-       makefile.filter(r'^\s*FC\s*=.*',  'FC = '  + spack_fc)
+       makefile.filter(r"^\s*CC\s*=.*",  f"CC = {spack_cc}")
+       makefile.filter(r"^\s*CXX\s*=.*", f"CXX = {spack_cxx}")
+       makefile.filter(r"^\s*F77\s*=.*", f"F77 = {spack_f77}")
+       makefile.filter(r"^\s*FC\s*=.*",  f"FC = {spack_fc}")
 
 
 `stream <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/stream/package.py>`_
@@ -181,16 +181,16 @@ well for storing variables:
 
    def edit(self, spec, prefix):
        config = {
-           'CC': 'cc',
-           'MAKE': 'make',
+           "CC": "cc",
+           "MAKE": "make",
        }
 
-       if '+blas' in spec:
-           config['BLAS_LIBS'] = spec['blas'].libs.joined()
+       if spec.satisfies("+blas"):
+           config["BLAS_LIBS"] = spec["blas"].libs.joined()
 
-       with open('make.inc', 'w') as inc:
+       with open("make.inc", "w") as inc:
            for key in config:
-               inc.write('{0} = {1}\n'.format(key, config[key]))
+               inc.write(f"{key} = {config[key]}\n")
 
 
 `elk <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/elk/package.py>`_
@@ -204,14 +204,14 @@ them in a list:
 
    def edit(self, spec, prefix):
        config = [
-           'INSTALL_DIR = {0}'.format(prefix),
-           'INCLUDE_DIR = $(INSTALL_DIR)/include',
-           'LIBRARY_DIR = $(INSTALL_DIR)/lib',
+           f"INSTALL_DIR = {prefix}",
+           "INCLUDE_DIR = $(INSTALL_DIR)/include",
+           "LIBRARY_DIR = $(INSTALL_DIR)/lib",
        ]
 
-       with open('make.inc', 'w') as inc:
+       with open("make.inc", "w") as inc:
            for var in config:
-               inc.write('{0}\n'.format(var))
+               inc.write(f"{var}\n")
 
 
 `hpl <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/hpl/package.py>`_
@@ -284,7 +284,7 @@ can tell Spack where to locate it like so:
 
 .. code-block:: python
 
-   build_directory = 'src'
+   build_directory = "src"
 
 
 ^^^^^^^^^^^^^^^^^^^
@@ -299,8 +299,8 @@ install the package:
 
    def install(self, spec, prefix):
        mkdir(prefix.bin)
-       install('foo', prefix.bin)
-       install_tree('lib', prefix.lib)
+       install("foo", prefix.bin)
+       install_tree("lib", prefix.lib)
 
 
 ^^^^^^^^^^^^^^^^^^^^^^

lib/spack/docs/build_systems/pythonpackage.rst

@@ -152,16 +152,16 @@ set. Once set, ``pypi`` will be used to define the ``homepage``,
 
 .. code-block:: python
 
-   homepage = 'https://pypi.org/project/setuptools/'
-   url      = 'https://pypi.org/packages/source/s/setuptools/setuptools-49.2.0.zip'
-   list_url = 'https://pypi.org/simple/setuptools/'
+   homepage = "https://pypi.org/project/setuptools/"
+   url      = "https://pypi.org/packages/source/s/setuptools/setuptools-49.2.0.zip"
+   list_url = "https://pypi.org/simple/setuptools/"
 
 
 is equivalent to:
 
 .. code-block:: python
 
-   pypi = 'setuptools/setuptools-49.2.0.zip'
+   pypi = "setuptools/setuptools-49.2.0.zip"
 
 
 If a package has a different homepage listed on PyPI, you can
@@ -208,7 +208,7 @@ dependencies to your package:
 
 .. code-block:: python
 
-   depends_on('py-setuptools@42:', type='build')
+   depends_on("py-setuptools@42:", type="build")
 
 
 Note that ``py-wheel`` is already listed as a build dependency in the
@@ -232,7 +232,7 @@ Look for dependencies under the following keys:
 * ``dependencies`` under ``[project]``
 
   These packages are required for building and installation. You can
-  add them with ``type=('build', 'run')``.
+  add them with ``type=("build", "run")``.
 
 * ``[project.optional-dependencies]``
 
@@ -279,12 +279,12 @@ distutils library, and has almost the exact same API. In addition to
 * ``setup_requires``
 
   These packages are usually only needed at build-time, so you can
-  add them with ``type='build'``.
+  add them with ``type="build"``.
 
 * ``install_requires``
 
   These packages are required for building and installation. You can
-  add them with ``type=('build', 'run')``.
+  add them with ``type=("build", "run")``.
 
 * ``extras_require``
 
@@ -296,7 +296,7 @@ distutils library, and has almost the exact same API. In addition to
 
   These are packages that are required to run the unit tests for the
   package. These dependencies can be specified using the
-  ``type='test'`` dependency type. However, the PyPI tarballs rarely
+  ``type="test"`` dependency type. However, the PyPI tarballs rarely
   contain unit tests, so there is usually no reason to add these.
 
 See https://setuptools.pypa.io/en/latest/userguide/dependency_management.html
@@ -321,7 +321,7 @@ older versions of flit may use the following keys:
 * ``requires`` under ``[tool.flit.metadata]``
 
   These packages are required for building and installation. You can
-  add them with ``type=('build', 'run')``.
+  add them with ``type=("build", "run")``.
 
 * ``[tool.flit.metadata.requires-extra]``
 
@@ -434,12 +434,12 @@ the BLAS/LAPACK library you want pkg-config to search for:
 
 .. code-block:: python
 
-   depends_on('py-pip@22.1:', type='build')
+   depends_on("py-pip@22.1:", type="build")
 
    def config_settings(self, spec, prefix):
        return {
-           'blas': spec['blas'].libs.names[0],
-           'lapack': spec['lapack'].libs.names[0],
+           "blas": spec["blas"].libs.names[0],
+           "lapack": spec["lapack"].libs.names[0],
        }
 
 
@@ -463,10 +463,10 @@ has an optional dependency on ``libyaml`` that can be enabled like so:
 
    def global_options(self, spec, prefix):
        options = []
-       if '+libyaml' in spec:
-           options.append('--with-libyaml')
+       if spec.satisfies("+libyaml"):
+           options.append("--with-libyaml")
        else:
-           options.append('--without-libyaml')
+           options.append("--without-libyaml")
        return options
 
 
@@ -492,10 +492,10 @@ allows you to specify the directories to search for ``libyaml``:
 
    def install_options(self, spec, prefix):
        options = []
-       if '+libyaml' in spec:
+       if spec.satisfies("+libyaml"):
            options.extend([
-               spec['libyaml'].libs.search_flags,
-               spec['libyaml'].headers.include_flags,
+               spec["libyaml"].libs.search_flags,
+               spec["libyaml"].headers.include_flags,
            ])
        return options
 
@@ -556,7 +556,7 @@ detected are wrong, you can provide the names yourself by overriding
 
 .. code-block:: python
 
-   import_modules = ['six']
+   import_modules = ["six"]
 
 
 Sometimes the list of module names to import depends on how the
@@ -571,9 +571,9 @@ This can be expressed like so:
 
    @property
    def import_modules(self):
-       modules = ['yaml']
-       if '+libyaml' in self.spec:
-           modules.append('yaml.cyaml')
+       modules = ["yaml"]
+       if self.spec.satisfies("+libyaml"):
+           modules.append("yaml.cyaml")
        return modules
 
 
@@ -586,14 +586,14 @@ Instead of defining the ``import_modules`` explicitly, only the subset
 of module names to be skipped can be defined by using ``skip_modules``.
 If a defined module has submodules, they are skipped as well, e.g.,
 in case the ``plotting`` modules should be excluded from the
-automatically detected ``import_modules`` ``['nilearn', 'nilearn.surface',
-'nilearn.plotting', 'nilearn.plotting.data']`` set:
+automatically detected ``import_modules`` ``["nilearn", "nilearn.surface",
+"nilearn.plotting", "nilearn.plotting.data"]`` set:
 
 .. code-block:: python
 
-        skip_modules = ['nilearn.plotting']
+        skip_modules = ["nilearn.plotting"]
 
-This will set ``import_modules`` to ``['nilearn', 'nilearn.surface']``
+This will set ``import_modules`` to ``["nilearn", "nilearn.surface"]``
 
 Import tests can be run during the installation using ``spack install
 --test=root`` or at any time after the installation using
@@ -612,11 +612,11 @@ after the ``install`` phase:
 
 .. code-block:: python
 
-   @run_after('install')
+   @run_after("install")
    @on_package_attributes(run_tests=True)
    def install_test(self):
-       with working_dir('spack-test', create=True):
-           python('-c', 'import numpy; numpy.test("full", verbose=2)')
+       with working_dir("spack-test", create=True):
+           python("-c", "import numpy; numpy.test('full', verbose=2)")
 
 
 when testing is enabled during the installation (i.e., ``spack install
@@ -638,7 +638,7 @@ provides Python bindings in a ``python`` directory, you can use:
 
 .. code-block:: python
 
-   build_directory = 'python'
+   build_directory = "python"
 
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

lib/spack/docs/build_systems/rocmpackage.rst

@@ -81,28 +81,27 @@ class of your package.  For example, you can add it to your
     class MyRocmPackage(CMakePackage, ROCmPackage):
         ...
         # Ensure +rocm and amdgpu_targets are passed to dependencies
-        depends_on('mydeppackage', when='+rocm')
+        depends_on("mydeppackage", when="+rocm")
         for val in ROCmPackage.amdgpu_targets:
-            depends_on('mydeppackage amdgpu_target={0}'.format(val),
-                       when='amdgpu_target={0}'.format(val))
+            depends_on(f"mydeppackage amdgpu_target={val}",
+                       when=f"amdgpu_target={val}")
         ...
 
         def cmake_args(self):
             spec = self.spec
             args = []
             ...
-            if '+rocm' in spec:
+            if spec.satisfies("+rocm"):
                 # Set up the hip macros needed by the build
                 args.extend([
-                    '-DENABLE_HIP=ON',
-                    '-DHIP_ROOT_DIR={0}'.format(spec['hip'].prefix)])
-                rocm_archs = spec.variants['amdgpu_target'].value
-                if 'none' not in rocm_archs:
-                    args.append('-DHIP_HIPCC_FLAGS=--amdgpu-target={0}'
-                                .format(",".join(rocm_archs)))
+                    "-DENABLE_HIP=ON",
+                    f"-DHIP_ROOT_DIR={spec['hip'].prefix}"])
+                rocm_archs = spec.variants["amdgpu_target"].value
+                if "none" not in rocm_archs:
+                    args.append(f"-DHIP_HIPCC_FLAGS=--amdgpu-target={','.join(rocm_archs}")
             else:
                 # Ensure build with hip is disabled
-                args.append('-DENABLE_HIP=OFF')
+                args.append("-DENABLE_HIP=OFF")
             ...
             return args
         ...
@@ -114,7 +113,7 @@ build.
 
 This example also illustrates how to check for the ``rocm`` variant using
 ``self.spec`` and how to retrieve the ``amdgpu_target`` variant's value
-using ``self.spec.variants['amdgpu_target'].value``.
+using ``self.spec.variants["amdgpu_target"].value``.
 
 All five packages using ``ROCmPackage`` as of January 2021 also use the
 :ref:`CudaPackage <cudapackage>`. So it is worth looking at those packages

lib/spack/docs/build_systems/sconspackage.rst

@@ -57,7 +57,7 @@ overridden like so:
 .. code-block:: python
 
    def test(self):
-       scons('check')
+       scons("check")
 
 
 ^^^^^^^^^^^^^^^
@@ -88,7 +88,7 @@ base class already contains:
 
 .. code-block:: python
 
-   depends_on('scons', type='build')
+   depends_on("scons", type="build")
 
 
 If you want to specify a particular version requirement, you can override
@@ -96,7 +96,7 @@ this in your package:
 
 .. code-block:: python
 
-   depends_on('scons@2.3.0:', type='build')
+   depends_on("scons@2.3.0:", type="build")
 
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -238,14 +238,14 @@ the package build phase. This is done by overriding ``build_args`` like so:
 
    def build_args(self, spec, prefix):
        args = [
-         'PREFIX={0}'.format(prefix),
-         'ZLIB={0}'.format(spec['zlib'].prefix),
+         f"PREFIX={prefix}",
+         f"ZLIB={spec['zlib'].prefix}",
        ]
 
-       if '+debug' in spec:
-           args.append('DEBUG=yes')
+       if spec.satisfies("+debug"):
+           args.append("DEBUG=yes")
        else:
-           args.append('DEBUG=no')
+           args.append("DEBUG=no")
 
        return args
 
@@ -275,8 +275,8 @@ environment variables. For example, cantera has the following option:
    * env_vars: [ string ]
        Environment variables to propagate through to SCons. Either the
        string "all" or a comma separated list of variable names, e.g.
-       'LD_LIBRARY_PATH,HOME'.
-       - default: 'LD_LIBRARY_PATH,PYTHONPATH'
+       "LD_LIBRARY_PATH,HOME".
+       - default: "LD_LIBRARY_PATH,PYTHONPATH"
 
 
 In the case of cantera, using ``env_vars=all`` allows us to use

lib/spack/docs/conf.py

@@ -204,6 +204,7 @@ def setup(sphinx):
     ("py:class", "clingo.Control"),
     ("py:class", "six.moves.urllib.parse.ParseResult"),
     ("py:class", "TextIO"),
+    ("py:class", "hashlib._Hash"),
     # Spack classes that are private and we don't want to expose
     ("py:class", "spack.provider_index._IndexBase"),
     ("py:class", "spack.repo._PrependFileLoader"),

lib/spack/docs/config_yaml.rst

@@ -304,3 +304,17 @@ To work properly, this requires your terminal to reset its title after
 Spack has finished its work, otherwise Spack's status information will
 remain in the terminal's title indefinitely. Most terminals should already
 be set up this way and clear Spack's status information.
+
+-----------
+``aliases``
+-----------
+
+Aliases can be used to define new Spack commands. They can be either shortcuts
+for longer commands or include specific arguments for convenience. For instance,
+if users want to use ``spack install``'s ``-v`` argument all the time, they can
+create a new alias called ``inst`` that will always call ``install -v``:
+
+.. code-block:: yaml
+
+   aliases:
+     inst: install -v

lib/spack/docs/images/strumpack_virtuals.svg

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lib/spack/docs/module_file_support.rst

@@ -519,11 +519,11 @@ inspections and customize them per-module-set.
 
   modules:
     prefix_inspections:
-      bin:
+      ./bin:
         - PATH
-      man:
+      ./man:
         - MANPATH
-      '':
+      ./:
         - CMAKE_PREFIX_PATH
 
 Prefix inspections are only applied if the relative path inside the
@@ -579,7 +579,7 @@ the view.
        view_relative_modules:
          use_view: my_view
        prefix_inspections:
-         bin:
+         ./bin:
            - PATH
      view:
        my_view:

lib/spack/docs/packaging_guide.rst

@@ -1549,7 +1549,7 @@ its value:
 
     def configure_args(self):
         ...
-        if "+shared" in self.spec:
+        if self.spec.satisfies("+shared"):
             extra_args.append("--enable-shared")
         else:
             extra_args.append("--disable-shared")
@@ -1636,7 +1636,7 @@ Within a package recipe a multi-valued variant is tested using a ``key=value`` s
 
   .. code-block:: python
 
-    if "languages=jit" in spec:
+    if spec.satisfies("languages=jit"):
         options.append("--enable-host-shared")
 
 """""""""""""""""""""""""""""""""""""""""""
@@ -2352,7 +2352,7 @@ the following at the command line of a bash shell:
 
 .. code-block:: console
 
-   $ for i in {1..12}; do nohup spack install -j 4 mpich@3.3.2 >> mpich_install.txt 2>&1 &; done
+   $ for i in {1..12}; do nohup spack install -j 4 mpich@3.3.2 >> mpich_install.txt 2>&1 & done
 
 .. note::
 
@@ -2557,9 +2557,10 @@ Conditional dependencies
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
 You may have a package that only requires a dependency under certain
-conditions. For example, you may have a package that has optional MPI support,
-- MPI is only a dependency when you want to enable MPI support for the
-package. In that case, you could say something like:
+conditions. For example, you may have a package with optional MPI support.
+You would then provide a variant to reflect that the feature is optional
+and specify the MPI dependency only applies when MPI support is enabled.
+In that case, you could say something like:
 
 .. code-block:: python
 
@@ -2567,13 +2568,39 @@ package. In that case, you could say something like:
 
    depends_on("mpi", when="+mpi")
 
-``when`` can include constraints on the variant, version, compiler, etc. and
-the :mod:`syntax<spack.spec>` is the same as for Specs written on the command
-line.
 
-If a dependency/feature of a package isn't typically used, you can save time
-by making it conditional (since Spack will not build the dependency unless it
-is required for the Spec).
+Suppose the above package also has, since version 3, optional `Trilinos`
+support and you want them both to build either with or without MPI. Further
+suppose you require a version of `Trilinos` no older than 12.6. In that case,
+the `trilinos` variant and dependency directives would be:
+
+.. code-block:: python
+
+   variant("trilinos", default=False, description="Enable Trilinos support")
+
+   depends_on("trilinos@12.6:", when="@3: +trilinos")
+   depends_on("trilinos@12.6: +mpi", when="@3: +trilinos +mpi")
+
+
+Alternatively, you could use the `when` context manager to equivalently specify
+the `trilinos` variant dependencies as follows:
+
+.. code-block:: python
+
+   with when("@3: +trilinos"):
+       depends_on("trilinos@12.6:")
+       depends_on("trilinos +mpi", when="+mpi")
+
+
+The argument to ``when`` in either case can include any Spec constraints that
+are supported on the command line using the same :ref:`syntax <sec-specs>`.
+
+.. note::
+
+   If a dependency isn't typically used, you can save time by making it
+   conditional since Spack will not build the dependency unless it is
+   required for the Spec.
+
 
 .. _dependency_dependency_patching:
 
@@ -2661,60 +2688,6 @@ appear in the package file (or in this case, in the list).
    right version. If two packages depend on ``binutils`` patched *the
    same* way, they can both use a single installation of ``binutils``.
 
-.. _setup-dependent-environment:
-
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-Influence how dependents are built or run
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Spack provides a mechanism for dependencies to influence the
-environment of their dependents by overriding  the
-:meth:`setup_dependent_run_environment <spack.package_base.PackageBase.setup_dependent_run_environment>`
-or the
-:meth:`setup_dependent_build_environment <spack.builder.Builder.setup_dependent_build_environment>`
-methods.
-The Qt package, for instance, uses this call:
-
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/qt/package.py
-   :pyobject: Qt.setup_dependent_build_environment
-   :linenos:
-
-to set the ``QTDIR`` environment variable so that packages
-that depend on a particular Qt installation will find it.
-Another good example of how a dependency can influence
-the build environment of dependents is the Python package:
-
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/python/package.py
-   :pyobject: Python.setup_dependent_build_environment
-   :linenos:
-
-In the method above it is ensured that any package that depends on Python
-will have the ``PYTHONPATH``, ``PYTHONHOME`` and ``PATH`` environment
-variables set appropriately before starting the installation. To make things
-even simpler the ``python setup.py`` command is also inserted into the module
-scope of dependents by overriding a third method called
-:meth:`setup_dependent_package <spack.package_base.PackageBase.setup_dependent_package>`
-:
-
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/python/package.py
-   :pyobject: Python.setup_dependent_package
-   :linenos:
-
-This allows most python packages to have a very simple install procedure,
-like the following:
-
-.. code-block:: python
-
-   def install(self, spec, prefix):
-       setup_py("install", "--prefix={0}".format(prefix))
-
-Finally the Python package takes also care of the modifications to ``PYTHONPATH``
-to allow dependencies to run correctly:
-
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/python/package.py
-    :pyobject: Python.setup_dependent_run_environment
-    :linenos:
-
 
 .. _packaging_conflicts:
 
@@ -2859,6 +2832,70 @@ variant(s) are selected.  This may be accomplished with conditional
        extends("python", when="+python")
        ...
 
+.. _setup-environment:
+
+--------------------------------------------
+Runtime and build time environment variables
+--------------------------------------------
+
+Spack provides a few methods to help package authors set up the required environment variables for
+their package. Environment variables typically depend on how the package is used: variables that
+make sense during the build phase may not be needed at runtime, and vice versa. Further, sometimes
+it makes sense to let a dependency set the environment variables for its dependents. To allow all
+this, Spack provides four different methods that can be overridden in a package:
+
+1. :meth:`setup_build_environment <spack.builder.Builder.setup_build_environment>`
+2. :meth:`setup_run_environment <spack.package_base.PackageBase.setup_run_environment>`
+3. :meth:`setup_dependent_build_environment <spack.builder.Builder.setup_dependent_build_environment>`
+4. :meth:`setup_dependent_run_environment <spack.package_base.PackageBase.setup_dependent_run_environment>`
+
+The Qt package, for instance, uses this call:
+
+.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/qt/package.py
+   :pyobject: Qt.setup_dependent_build_environment
+   :linenos:
+
+to set the ``QTDIR`` environment variable so that packages that depend on a particular Qt
+installation will find it.
+
+The following diagram will give you an idea when each of these methods is called in a build
+context:
+
+.. image:: images/setup_env.png
+   :align: center
+
+Notice that ``setup_dependent_run_environment`` can be called multiple times, once for each
+dependent package, whereas ``setup_run_environment`` is called only once for the package itself.
+This means that the former should only be used if the environment variables depend on the dependent
+package, whereas the latter should be used if the environment variables depend only on the package
+itself.
+
+--------------------------------
+Setting package module variables
+--------------------------------
+
+Apart from modifying environment variables of the dependent package, you can also define Python
+variables to be used by the dependent. This is done by implementing
+:meth:`setup_dependent_package <spack.package_base.PackageBase.setup_dependent_package>`. An
+example of this can be found in the ``Python`` package:
+
+.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/python/package.py
+   :pyobject: Python.setup_dependent_package
+   :linenos:
+
+This allows Python packages to directly use these variables:
+
+.. code-block:: python
+
+   def install(self, spec, prefix):
+       ...
+       install("script.py", python_platlib)
+
+.. note::
+
+   We recommend using ``setup_dependent_package`` sparingly, as it is not always clear where
+   global variables are coming from when editing a ``package.py`` file.
+
 -----
 Views
 -----
@@ -2937,6 +2974,33 @@ The ``provides("mpi")`` call tells Spack that the ``mpich`` package
 can be used to satisfy the dependency of any package that
 ``depends_on("mpi")``.
 
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Providing multiple virtuals simultaneously
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Packages can provide more than one virtual dependency. Sometimes, due to implementation details,
+there are subsets of those virtuals that need to be provided together by the same package.
+
+A well-known example is ``openblas``, which provides both the ``lapack`` and ``blas`` API in a single ``libopenblas``
+library. A package that needs ``lapack`` and ``blas`` must either use ``openblas`` to provide both, or not use
+``openblas`` at all. It cannot pick one or the other.
+
+To express this constraint in a package, the two virtual dependencies must be listed in the same ``provides`` directive:
+
+.. code-block:: python
+
+   provides('blas', 'lapack')
+
+This makes it impossible to select ``openblas`` as a provider for one of the two
+virtual dependencies and not for the other. If you try to, Spack will report an error:
+
+.. code-block:: console
+
+   $ spack spec netlib-scalapack  ^[virtuals=lapack] openblas ^[virtuals=blas] atlas
+   ==> Error: concretization failed for the following reasons:
+
+      1. Package 'openblas' needs to provide both 'lapack' and 'blas' together, but provides only 'lapack'
+
 ^^^^^^^^^^^^^^^^^^^^
 Versioned Interfaces
 ^^^^^^^^^^^^^^^^^^^^
@@ -3439,6 +3503,56 @@ is equivalent to:
 Constraints from nested context managers are also combined together, but they are rarely
 needed or recommended.
 
+.. _default_args:
+
+------------------------
+Common default arguments
+------------------------
+
+Similarly, if directives have a common set of default arguments, you can
+group them together in a ``with default_args()`` block:
+
+.. code-block:: python
+
+   class PyExample(PythonPackage):
+
+       with default_args(type=("build", "run")):
+           depends_on("py-foo")
+           depends_on("py-foo@2:", when="@2:")
+           depends_on("py-bar")
+           depends_on("py-bz")
+
+The above is short for:
+
+.. code-block:: python
+
+   class PyExample(PythonPackage):
+
+       depends_on("py-foo", type=("build", "run"))
+       depends_on("py-foo@2:", when="@2:", type=("build", "run"))
+       depends_on("py-bar", type=("build", "run"))
+       depends_on("py-bz", type=("build", "run"))
+
+.. note::
+
+   The ``with when()`` context manager is composable, while ``with default_args()``
+   merely overrides the default. For example:
+
+   .. code-block:: python
+
+      with default_args(when="+feature"):
+          depends_on("foo")
+          depends_on("bar")
+          depends_on("baz", when="+baz")
+
+   is equivalent to:
+
+   .. code-block:: python
+
+      depends_on("foo", when="+feature")
+      depends_on("bar", when="+feature")
+      depends_on("baz", when="+baz")  # Note: not when="+feature+baz"
+
 .. _install-method:
 
 ------------------
@@ -3501,7 +3615,7 @@ need to override methods like ``configure_args``:
 
    def configure_args(self):
         args = ["--enable-cxx"] + self.enable_or_disable("libs")
-        if "libs=static" in self.spec:
+        if self.spec.satisfies("libs=static"):
             args.append("--with-pic")
         return args
 
@@ -3738,7 +3852,7 @@ Similarly, ``spack install example +feature build_system=autotools`` will pick
 the  ``AutotoolsBuilder`` and invoke ``./configure --with-my-feature``.
 
 Dependencies are always specified in the package class. When some dependencies
-depend on the choice of the build system, it is possible to use when conditions as 
+depend on the choice of the build system, it is possible to use when conditions as
 usual:
 
 .. code-block:: python
@@ -3756,7 +3870,7 @@ usual:
            depends_on("cmake@3.18:", when="@2.0:", type="build")
            depends_on("cmake@3:", type="build")
 
-       # Specify extra build dependencies used only in the configure script 
+       # Specify extra build dependencies used only in the configure script
        with when("build_system=autotools"):
            depends_on("perl", type="build")
            depends_on("pkgconfig", type="build")
@@ -4364,7 +4478,7 @@ for supported features, for instance:
 
 .. code-block:: python
 
-   if "avx512" in spec.target:
+   if spec.satisfies("target=avx512"):
        args.append("--with-avx512")
 
 The snippet above will append the ``--with-avx512`` item to a list of arguments only if the corresponding
@@ -6804,25 +6918,58 @@ the adapter role is to "emulate" a method resolution order like the one represen
 Specifying License Information
 ------------------------------
 
-A significant portion of software that Spack packages is open source. Most open
-source software is released under one or more common open source licenses.
-Specifying the specific license that a package is released under in a project's
-`package.py` is good practice. To specify a license, find the SPDX identifier for
-a project and then add it using the license directive:
+Most of the software in Spack is open source, and most open source software is released
+under one or more `common open source licenses <https://opensource.org/licenses/>`_.
+Specifying the license that a package is released under in a project's
+`package.py` is good practice. To specify a license, find the `SPDX identifier
+<https://spdx.org/licenses/>`_ for a project and then add it using the license
+directive:
 
 .. code-block:: python
 
    license("<SPDX Identifier HERE>")
 
+For example, the SPDX ID for the Apache Software License, version 2.0 is ``Apache-2.0``,
+so you'd write:
+
+.. code-block:: python
+
+   license("Apache-2.0")
+
+Or, for a dual-licensed package like Spack, you would use an `SPDX Expression
+<https://spdx.github.io/spdx-spec/v2-draft/SPDX-license-expressions/>`_ with both of its
+licenses:
+
+.. code-block:: python
+
+   license("Apache-2.0 OR MIT")
+
 Note that specifying a license without a when clause makes it apply to all
 versions and variants of the package, which might not actually be the case.
 For example, a project might have switched licenses at some point or have
 certain build configurations that include files that are licensed differently.
-To account for this, you can specify when licenses should be applied. For
-example, to specify that a specific license identifier should only apply
-to versionup to and including 1.5, you could write the following directive:
+Spack itself used to be under the ``LGPL-2.1`` license, until it was relicensed
+in version ``0.12`` in 2018.
+
+You can specify when a ``license()`` directive applies using with a ``when=``
+clause, just like other directives. For example, to specify that a specific
+license identifier should only apply to versions up to ``0.11``, but another
+license should apply for later versions, you could write:
 
 .. code-block:: python
 
-   license("...", when="@:1.5")
+   license("LGPL-2.1", when="@:0.11")
+   license("Apache-2.0 OR MIT", when="@0.12:")
 
+Note that unlike for most other directives, the ``when=`` constraints in the
+``license()`` directive can't intersect. Spack needs to be able to resolve
+exactly one license identifier expression for any given version. To specify
+*multiple* licenses, use SPDX expressions and operators as above. The operators
+you probably care most about are:
+
+* ``OR``: user chooses one license to adhere to; and
+* ``AND``: user has to adhere to all the licenses.
+
+You may also care about `license exceptions
+<https://spdx.org/licenses/exceptions-index.html>`_ that use the ``WITH`` operator,
+e.g. ``Apache-2.0 WITH LLVM-exception``.

lib/spack/docs/requirements.txt

@@ -6,8 +6,8 @@ python-levenshtein==0.23.0
 docutils==0.18.1
 pygments==2.16.1
 urllib3==2.0.7
-pytest==7.4.2
+pytest==7.4.3
 isort==5.12.0
-black==23.9.1
+black==23.10.1
 flake8==6.1.0
 mypy==1.6.1

lib/spack/external/__init__.py

@@ -18,7 +18,7 @@
 
 * Homepage: https://pypi.python.org/pypi/archspec
 * Usage: Labeling, comparison and detection of microarchitectures
-* Version: 0.2.1 (commit df43a1834460bf94516136951c4729a3100603ec)
+* Version: 0.2.2 (commit 1dc58a5776dd77e6fc6e4ba5626af5b1fb24996e)
 
 astunparse
 ----------------

lib/spack/external/archspec/__init__.py

@@ -1,2 +1,2 @@
 """Init file to avoid namespace packages"""
-__version__ = "0.2.1"
+__version__ = "0.2.2"

lib/spack/external/archspec/json/cpu/microarchitectures.json

@@ -2318,6 +2318,26 @@
         ]
       }
     },
+    "power10": {
+      "from": ["power9"],
+      "vendor": "IBM",
+      "generation": 10,
+      "features": [],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "11.1:",
+            "flags": "-mcpu={name} -mtune={name}"
+          }
+        ],
+        "clang": [
+          {
+            "versions": "11.0:",
+            "flags": "-mcpu={name} -mtune={name}"
+          }
+        ]
+      }
+    },
     "ppc64le": {
       "from": [],
       "vendor": "generic",
@@ -2405,6 +2425,29 @@
         ]
       }
     },
+    "power10le": {
+      "from": ["power9le"],
+      "vendor": "IBM",
+      "generation": 10,
+      "features": [],
+      "compilers": {
+        "gcc": [
+          {
+            "name": "power10",
+            "versions": "11.1:",
+            "flags": "-mcpu={name} -mtune={name}"
+          }
+        ],
+        "clang": [
+          {
+            "versions": "11.0:",
+            "family": "ppc64le",
+            "name": "power10",
+            "flags": "-mcpu={name} -mtune={name}"
+          }
+        ]
+      }
+    },
     "aarch64": {
       "from": [],
       "vendor": "generic",
@@ -2592,6 +2635,37 @@
         ]
       }
     },
+    "armv9.0a": {
+      "from": ["armv8.5a"],
+      "vendor": "generic",
+      "features": [],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "12:",
+            "flags": "-march=armv9-a -mtune=generic"
+          }
+        ],
+        "clang": [
+          {
+            "versions": "14:",
+            "flags": "-march=armv9-a -mtune=generic"
+          }
+        ],
+        "apple-clang": [
+          {
+            "versions": ":",
+            "flags": "-march=armv9-a -mtune=generic"
+          }
+        ],
+        "arm": [
+          {
+            "versions": ":",
+            "flags": "-march=armv9-a -mtune=generic"
+          }
+        ]
+      }
+    },
     "thunderx2": {
       "from": ["armv8.1a"],
       "vendor": "Cavium",
@@ -2813,8 +2887,12 @@
           ],
           "arm" : [
               {
-                  "versions": "20:",
+                  "versions": "20:21.9",
                   "flags" : "-march=armv8.2-a+fp16+rcpc+dotprod+crypto"
+              },
+              {
+                  "versions": "22:",
+                  "flags" : "-mcpu=neoverse-n1"
               }
           ],
           "nvhpc" : [
@@ -2942,7 +3020,7 @@
               },
 	            {
                   "versions": "22:",
-                  "flags" : "-march=armv8.4-a+sve+ssbs+fp16+bf16+crypto+i8mm+rng"
+                  "flags" : "-mcpu=neoverse-v1"
               }
           ],
           "nvhpc" : [
@@ -2954,6 +3032,126 @@
           ]
       }
     },
+    "neoverse_v2": {
+      "from": ["neoverse_n1", "armv9.0a"],
+      "vendor": "ARM",
+      "features": [
+          "fp",
+	  "asimd",
+	  "evtstrm",
+	  "aes",
+	  "pmull",
+	  "sha1",
+	  "sha2",
+	  "crc32",
+	  "atomics",
+	  "fphp",
+	  "asimdhp",
+	  "cpuid",
+	  "asimdrdm",
+	  "jscvt",
+	  "fcma",
+	  "lrcpc",
+	  "dcpop",
+	  "sha3",
+	  "sm3",
+	  "sm4",
+	  "asimddp",
+	  "sha512",
+	  "sve",
+	  "asimdfhm",
+	  "dit",
+	  "uscat",
+	  "ilrcpc",
+	  "flagm",
+	  "ssbs",
+	  "sb",
+	  "paca",
+	  "pacg",
+	  "dcpodp",
+	  "sve2",
+	  "sveaes",
+	  "svepmull",
+	  "svebitperm",
+	  "svesha3",
+	  "svesm4",
+	  "flagm2",
+	  "frint",
+	  "svei8mm",
+	  "svebf16",
+	  "i8mm",
+	  "bf16",
+	  "dgh",
+	  "bti"
+      ],
+      "compilers" : {
+          "gcc": [
+              {
+                  "versions": "4.8:5.99",
+                  "flags": "-march=armv8-a"
+              },
+              {
+                  "versions": "6:6.99",
+                  "flags" : "-march=armv8.1-a"
+              },
+              {
+                  "versions": "7.0:7.99",
+                  "flags" : "-march=armv8.2-a -mtune=cortex-a72"
+              },
+              {
+                  "versions": "8.0:8.99",
+                  "flags" : "-march=armv8.4-a+sve -mtune=cortex-a72"
+              },
+              {
+                  "versions": "9.0:9.99",
+                  "flags" : "-march=armv8.5-a+sve -mtune=cortex-a76"
+              },
+              {
+                  "versions": "10.0:11.99",
+                  "flags" : "-march=armv8.5-a+sve+sve2+i8mm+bf16 -mtune=cortex-a77"
+              },
+              {
+                  "versions": "12.0:12.99",
+                  "flags" : "-march=armv9-a+i8mm+bf16 -mtune=cortex-a710"
+              },
+	      {
+                  "versions": "13.0:",
+                  "flags" : "-mcpu=neoverse-v2"
+              }
+          ],
+          "clang" : [
+              {
+                  "versions": "9.0:10.99",
+                  "flags" : "-march=armv8.5-a+sve"
+              },
+              {
+                  "versions": "11.0:13.99",
+                  "flags" : "-march=armv8.5-a+sve+sve2+i8mm+bf16"
+              },
+              {
+                  "versions": "14.0:15.99",
+                  "flags" : "-march=armv9-a+i8mm+bf16"
+              },
+              {
+                  "versions": "16.0:",
+                  "flags" : "-mcpu=neoverse-v2"
+              }
+          ],
+          "arm" : [
+              {
+                  "versions": "23.04.0:",
+                  "flags" : "-mcpu=neoverse-v2"
+              }
+          ],
+          "nvhpc" : [
+              {
+                  "versions": "23.3:",
+                  "name": "neoverse-v2",
+                  "flags": "-tp {name}"
+              }
+          ]
+      }
+    },
     "m1": {
       "from": ["armv8.4a"],
       "vendor": "Apple",

lib/spack/llnl/util/tty/__init__.py

@@ -211,6 +211,7 @@ def info(message, *args, **kwargs):
                 stream.write(line + "\n")
         else:
             stream.write(indent + _output_filter(str(arg)) + "\n")
+    stream.flush()
 
 
 def verbose(message, *args, **kwargs):

lib/spack/spack/__init__.py

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 #: PEP440 canonical <major>.<minor>.<micro>.<devN> string
-__version__ = "0.21.0.dev0"
+__version__ = "0.21.0"
 spack_version = __version__
 
 

lib/spack/spack/audit.py

@@ -307,10 +307,17 @@ def _check_build_test_callbacks(pkgs, error_cls):
 
 @package_directives
 def _check_patch_urls(pkgs, error_cls):
-    """Ensure that patches fetched from GitHub have stable sha256 hashes."""
+    """Ensure that patches fetched from GitHub and GitLab have stable sha256
+    hashes."""
     github_patch_url_re = (
         r"^https?://(?:patch-diff\.)?github(?:usercontent)?\.com/"
-        ".+/.+/(?:commit|pull)/[a-fA-F0-9]*.(?:patch|diff)"
+        r".+/.+/(?:commit|pull)/[a-fA-F0-9]+\.(?:patch|diff)"
+    )
+    # Only .diff URLs have stable/full hashes:
+    # https://forum.gitlab.com/t/patches-with-full-index/29313
+    gitlab_patch_url_re = (
+        r"^https?://(?:.+)?gitlab(?:.+)/"
+        r".+/.+/-/(?:commit|merge_requests)/[a-fA-F0-9]+\.(?:patch|diff)"
     )
 
     errors = []
@@ -321,19 +328,27 @@ def _check_patch_urls(pkgs, error_cls):
                 if not isinstance(patch, spack.patch.UrlPatch):
                     continue
 
-                if not re.match(github_patch_url_re, patch.url):
-                    continue
-
-                full_index_arg = "?full_index=1"
-                if not patch.url.endswith(full_index_arg):
-                    errors.append(
-                        error_cls(
-                            "patch URL in package {0} must end with {1}".format(
-                                pkg_cls.name, full_index_arg
-                            ),
-                            [patch.url],
+                if re.match(github_patch_url_re, patch.url):
+                    full_index_arg = "?full_index=1"
+                    if not patch.url.endswith(full_index_arg):
+                        errors.append(
+                            error_cls(
+                                "patch URL in package {0} must end with {1}".format(
+                                    pkg_cls.name, full_index_arg
+                                ),
+                                [patch.url],
+                            )
+                        )
+                elif re.match(gitlab_patch_url_re, patch.url):
+                    if not patch.url.endswith(".diff"):
+                        errors.append(
+                            error_cls(
+                                "patch URL in package {0} must end with .diff".format(
+                                    pkg_cls.name
+                                ),
+                                [patch.url],
+                            )
                         )
-                    )
 
     return errors
 

lib/spack/spack/binary_distribution.py

@@ -5,11 +5,13 @@
 
 import codecs
 import collections
+import errno
 import hashlib
 import io
 import itertools
 import json
 import os
+import pathlib
 import re
 import shutil
 import sys
@@ -23,7 +25,7 @@
 import warnings
 from contextlib import closing, contextmanager
 from gzip import GzipFile
-from typing import Dict, List, NamedTuple, Optional, Tuple, Union
+from typing import Dict, List, NamedTuple, Optional, Set, Tuple
 from urllib.error import HTTPError, URLError
 
 import llnl.util.filesystem as fsys
@@ -31,6 +33,7 @@
 import llnl.util.tty as tty
 from llnl.util.filesystem import BaseDirectoryVisitor, mkdirp, visit_directory_tree
 
+import spack.caches
 import spack.cmd
 import spack.config as config
 import spack.database as spack_db
@@ -38,6 +41,9 @@
 import spack.hooks
 import spack.hooks.sbang
 import spack.mirror
+import spack.oci.image
+import spack.oci.oci
+import spack.oci.opener
 import spack.platforms
 import spack.relocate as relocate
 import spack.repo
@@ -47,6 +53,7 @@
 import spack.util.crypto
 import spack.util.file_cache as file_cache
 import spack.util.gpg
+import spack.util.path
 import spack.util.spack_json as sjson
 import spack.util.spack_yaml as syaml
 import spack.util.timer as timer
@@ -59,8 +66,9 @@
 from spack.stage import Stage
 from spack.util.executable import which
 
-_build_cache_relative_path = "build_cache"
-_build_cache_keys_relative_path = "_pgp"
+BUILD_CACHE_RELATIVE_PATH = "build_cache"
+BUILD_CACHE_KEYS_RELATIVE_PATH = "_pgp"
+CURRENT_BUILD_CACHE_LAYOUT_VERSION = 1
 
 
 class BuildCacheDatabase(spack_db.Database):
@@ -124,25 +132,25 @@ class BinaryCacheIndex:
     mean we should have paid the price to update the cache earlier?
     """
 
-    def __init__(self, cache_root):
-        self._index_cache_root = cache_root
+    def __init__(self, cache_root: Optional[str] = None):
+        self._index_cache_root: str = cache_root or binary_index_location()
 
         # the key associated with the serialized _local_index_cache
         self._index_contents_key = "contents.json"
 
         # a FileCache instance storing copies of remote binary cache indices
-        self._index_file_cache = None
+        self._index_file_cache: Optional[file_cache.FileCache] = None
 
         # stores a map of mirror URL to index hash and cache key (index path)
-        self._local_index_cache = None
+        self._local_index_cache: Optional[dict] = None
 
         # hashes of remote indices already ingested into the concrete spec
         # cache (_mirrors_for_spec)
-        self._specs_already_associated = set()
+        self._specs_already_associated: Set[str] = set()
 
         # mapping from mirror urls to the time.time() of the last index fetch and a bool indicating
         # whether the fetch succeeded or not.
-        self._last_fetch_times = {}
+        self._last_fetch_times: Dict[str, float] = {}
 
         # _mirrors_for_spec is a dictionary mapping DAG hashes to lists of
         # entries indicating mirrors where that concrete spec can be found.
@@ -152,7 +160,7 @@ def __init__(self, cache_root):
         #     - the concrete spec itself, keyed by ``spec`` (including the
         #           full hash, since the dag hash may match but we want to
         #           use the updated source if available)
-        self._mirrors_for_spec = {}
+        self._mirrors_for_spec: Dict[str, dict] = {}
 
     def _init_local_index_cache(self):
         if not self._index_file_cache:
@@ -471,14 +479,18 @@ def _fetch_and_cache_index(self, mirror_url, cache_entry={}):
             FetchIndexError
         """
         # TODO: get rid of this request, handle 404 better
-        if not web_util.url_exists(
-            url_util.join(mirror_url, _build_cache_relative_path, "index.json")
+        scheme = urllib.parse.urlparse(mirror_url).scheme
+
+        if scheme != "oci" and not web_util.url_exists(
+            url_util.join(mirror_url, BUILD_CACHE_RELATIVE_PATH, "index.json")
         ):
             return False
 
-        etag = cache_entry.get("etag", None)
-        if etag:
-            fetcher = EtagIndexFetcher(mirror_url, etag)
+        if scheme == "oci":
+            # TODO: Actually etag and OCI are not mutually exclusive...
+            fetcher = OCIIndexFetcher(mirror_url, cache_entry.get("index_hash", None))
+        elif cache_entry.get("etag"):
+            fetcher = EtagIndexFetcher(mirror_url, cache_entry["etag"])
         else:
             fetcher = DefaultIndexFetcher(
                 mirror_url, local_hash=cache_entry.get("index_hash", None)
@@ -519,15 +531,8 @@ def binary_index_location():
     return spack.util.path.canonicalize_path(cache_root)
 
 
-def _binary_index():
-    """Get the singleton store instance."""
-    return BinaryCacheIndex(binary_index_location())
-
-
-#: Singleton binary_index instance
-binary_index: Union[BinaryCacheIndex, llnl.util.lang.Singleton] = llnl.util.lang.Singleton(
-    _binary_index
-)
+#: Default binary cache index instance
+BINARY_INDEX: BinaryCacheIndex = llnl.util.lang.Singleton(BinaryCacheIndex)  # type: ignore
 
 
 class NoOverwriteException(spack.error.SpackError):
@@ -596,6 +601,10 @@ def __init__(self, msg):
         super().__init__(msg)
 
 
+class InvalidMetadataFile(spack.error.SpackError):
+    pass
+
+
 class UnsignedPackageException(spack.error.SpackError):
     """
     Raised if installation of unsigned package is attempted without
@@ -610,11 +619,11 @@ def compute_hash(data):
 
 
 def build_cache_relative_path():
-    return _build_cache_relative_path
+    return BUILD_CACHE_RELATIVE_PATH
 
 
 def build_cache_keys_relative_path():
-    return _build_cache_keys_relative_path
+    return BUILD_CACHE_KEYS_RELATIVE_PATH
 
 
 def build_cache_prefix(prefix):
@@ -622,21 +631,14 @@ def build_cache_prefix(prefix):
 
 
 def buildinfo_file_name(prefix):
-    """
-    Filename of the binary package meta-data file
-    """
-    return os.path.join(prefix, ".spack/binary_distribution")
+    """Filename of the binary package meta-data file"""
+    return os.path.join(prefix, ".spack", "binary_distribution")
 
 
 def read_buildinfo_file(prefix):
-    """
-    Read buildinfo file
-    """
-    filename = buildinfo_file_name(prefix)
-    with open(filename, "r") as inputfile:
-        content = inputfile.read()
-        buildinfo = syaml.load(content)
-    return buildinfo
+    """Read buildinfo file"""
+    with open(buildinfo_file_name(prefix), "r") as f:
+        return syaml.load(f)
 
 
 class BuildManifestVisitor(BaseDirectoryVisitor):
@@ -819,18 +821,6 @@ def tarball_path_name(spec, ext):
     return os.path.join(tarball_directory_name(spec), tarball_name(spec, ext))
 
 
-def checksum_tarball(file):
-    # calculate sha256 hash of tar file
-    block_size = 65536
-    hasher = hashlib.sha256()
-    with open(file, "rb") as tfile:
-        buf = tfile.read(block_size)
-        while len(buf) > 0:
-            hasher.update(buf)
-            buf = tfile.read(block_size)
-    return hasher.hexdigest()
-
-
 def select_signing_key(key=None):
     if key is None:
         keys = spack.util.gpg.signing_keys()
@@ -1147,14 +1137,17 @@ def gzip_compressed_tarfile(path):
     # compresslevel=6 gzip default: llvm takes 4mins, roughly 2.1GB
     # compresslevel=9 python default: llvm takes 12mins, roughly 2.1GB
     # So we follow gzip.
-    with open(path, "wb") as fileobj, closing(
-        GzipFile(filename="", mode="wb", compresslevel=6, mtime=0, fileobj=fileobj)
-    ) as gzip_file, tarfile.TarFile(name="", mode="w", fileobj=gzip_file) as tar:
-        yield tar
+    with open(path, "wb") as f, ChecksumWriter(f) as inner_checksum, closing(
+        GzipFile(filename="", mode="wb", compresslevel=6, mtime=0, fileobj=inner_checksum)
+    ) as gzip_file, ChecksumWriter(gzip_file) as outer_checksum, tarfile.TarFile(
+        name="", mode="w", fileobj=outer_checksum
+    ) as tar:
+        yield tar, inner_checksum, outer_checksum
 
 
-def _tarinfo_name(p: str):
-    return p.lstrip("/")
+def _tarinfo_name(absolute_path: str, *, _path=pathlib.PurePath) -> str:
+    """Compute tarfile entry name as the relative path from the (system) root."""
+    return _path(*_path(absolute_path).parts[1:]).as_posix()
 
 
 def tarfile_of_spec_prefix(tar: tarfile.TarFile, prefix: str) -> None:
@@ -1234,8 +1227,88 @@ def tarfile_of_spec_prefix(tar: tarfile.TarFile, prefix: str) -> None:
         dir_stack.extend(reversed(new_dirs))  # we pop, so reverse to stay alphabetical
 
 
+class ChecksumWriter(io.BufferedIOBase):
+    """Checksum writer computes a checksum while writing to a file."""
+
+    myfileobj = None
+
+    def __init__(self, fileobj, algorithm=hashlib.sha256):
+        self.fileobj = fileobj
+        self.hasher = algorithm()
+        self.length = 0
+
+    def hexdigest(self):
+        return self.hasher.hexdigest()
+
+    def write(self, data):
+        if isinstance(data, (bytes, bytearray)):
+            length = len(data)
+        else:
+            data = memoryview(data)
+            length = data.nbytes
+
+        if length > 0:
+            self.fileobj.write(data)
+            self.hasher.update(data)
+
+        self.length += length
+
+        return length
+
+    def read(self, size=-1):
+        raise OSError(errno.EBADF, "read() on write-only object")
+
+    def read1(self, size=-1):
+        raise OSError(errno.EBADF, "read1() on write-only object")
+
+    def peek(self, n):
+        raise OSError(errno.EBADF, "peek() on write-only object")
+
+    @property
+    def closed(self):
+        return self.fileobj is None
+
+    def close(self):
+        fileobj = self.fileobj
+        if fileobj is None:
+            return
+        self.fileobj.close()
+        self.fileobj = None
+
+    def flush(self):
+        self.fileobj.flush()
+
+    def fileno(self):
+        return self.fileobj.fileno()
+
+    def rewind(self):
+        raise OSError("Can't rewind while computing checksum")
+
+    def readable(self):
+        return False
+
+    def writable(self):
+        return True
+
+    def seekable(self):
+        return True
+
+    def tell(self):
+        return self.fileobj.tell()
+
+    def seek(self, offset, whence=io.SEEK_SET):
+        # In principle forward seek is possible with b"0" padding,
+        # but this is not implemented.
+        if offset == 0 and whence == io.SEEK_CUR:
+            return
+        raise OSError("Can't seek while computing checksum")
+
+    def readline(self, size=-1):
+        raise OSError(errno.EBADF, "readline() on write-only object")
+
+
 def _do_create_tarball(tarfile_path: str, binaries_dir: str, buildinfo: dict):
-    with gzip_compressed_tarfile(tarfile_path) as tar:
+    with gzip_compressed_tarfile(tarfile_path) as (tar, inner_checksum, outer_checksum):
         # Tarball the install prefix
         tarfile_of_spec_prefix(tar, binaries_dir)
 
@@ -1247,6 +1320,8 @@ def _do_create_tarball(tarfile_path: str, binaries_dir: str, buildinfo: dict):
         tarinfo.mode = 0o644
         tar.addfile(tarinfo, io.BytesIO(bstring))
 
+    return inner_checksum.hexdigest(), outer_checksum.hexdigest()
+
 
 class PushOptions(NamedTuple):
     #: Overwrite existing tarball/metadata files in buildcache
@@ -1322,20 +1397,16 @@ def _build_tarball_in_stage_dir(spec: Spec, out_url: str, stage_dir: str, option
     # create info for later relocation and create tar
     buildinfo = get_buildinfo_dict(spec)
 
-    _do_create_tarball(tarfile_path, binaries_dir, buildinfo)
-
-    # get the sha256 checksum of the tarball
-    checksum = checksum_tarball(tarfile_path)
+    checksum, _ = _do_create_tarball(tarfile_path, binaries_dir, buildinfo)
 
     # add sha256 checksum to spec.json
-
     with open(spec_file, "r") as inputfile:
         content = inputfile.read()
         if spec_file.endswith(".json"):
             spec_dict = sjson.load(content)
         else:
             raise ValueError("{0} not a valid spec file type".format(spec_file))
-    spec_dict["buildcache_layout_version"] = 1
+    spec_dict["buildcache_layout_version"] = CURRENT_BUILD_CACHE_LAYOUT_VERSION
     spec_dict["binary_cache_checksum"] = {"hash_algorithm": "sha256", "hash": checksum}
 
     with open(specfile_path, "w") as outfile:
@@ -1371,10 +1442,21 @@ def _build_tarball_in_stage_dir(spec: Spec, out_url: str, stage_dir: str, option
     return None
 
 
+class NotInstalledError(spack.error.SpackError):
+    """Raised when a spec is not installed but picked to be packaged."""
+
+    def __init__(self, specs: List[Spec]):
+        super().__init__(
+            "Cannot push non-installed packages",
+            ", ".join(s.cformat("{name}{@version}{/hash:7}") for s in specs),
+        )
+
+
 def specs_to_be_packaged(
     specs: List[Spec], root: bool = True, dependencies: bool = True
 ) -> List[Spec]:
     """Return the list of nodes to be packaged, given a list of specs.
+    Raises NotInstalledError if a spec is not installed but picked to be packaged.
 
     Args:
         specs: list of root specs to be processed
@@ -1382,19 +1464,35 @@ def specs_to_be_packaged(
         dependencies: include the dependencies of each
             spec in the nodes
     """
+
     if not root and not dependencies:
         return []
-    elif dependencies:
-        nodes = traverse.traverse_nodes(specs, root=root, deptype="all")
-    else:
-        nodes = set(specs)
 
-    # Limit to installed non-externals.
-    packageable = lambda n: not n.external and n.installed
-
-    # Mass install check
+    # Filter packageable roots
     with spack.store.STORE.db.read_transaction():
-        return list(filter(packageable, nodes))
+        if root:
+            # Error on uninstalled roots, when roots are requested
+            uninstalled_roots = list(s for s in specs if not s.installed)
+            if uninstalled_roots:
+                raise NotInstalledError(uninstalled_roots)
+            roots = specs
+        else:
+            roots = []
+
+        if dependencies:
+            # Error on uninstalled deps, when deps are requested
+            deps = list(
+                traverse.traverse_nodes(
+                    specs, deptype="all", order="breadth", root=False, key=traverse.by_dag_hash
+                )
+            )
+            uninstalled_deps = list(s for s in deps if not s.installed)
+            if uninstalled_deps:
+                raise NotInstalledError(uninstalled_deps)
+        else:
+            deps = []
+
+    return [s for s in itertools.chain(roots, deps) if not s.external]
 
 
 def push(spec: Spec, mirror_url: str, options: PushOptions):
@@ -1467,6 +1565,42 @@ def _delete_staged_downloads(download_result):
     download_result["specfile_stage"].destroy()
 
 
+def _get_valid_spec_file(path: str, max_supported_layout: int) -> Tuple[Dict, int]:
+    """Read and validate a spec file, returning the spec dict with its layout version, or raising
+    InvalidMetadataFile if invalid."""
+    try:
+        with open(path, "rb") as f:
+            binary_content = f.read()
+    except OSError:
+        raise InvalidMetadataFile(f"No such file: {path}")
+
+    # In the future we may support transparently decompressing compressed spec files.
+    if binary_content[:2] == b"\x1f\x8b":
+        raise InvalidMetadataFile("Compressed spec files are not supported")
+
+    try:
+        as_string = binary_content.decode("utf-8")
+        if path.endswith(".json.sig"):
+            spec_dict = Spec.extract_json_from_clearsig(as_string)
+        else:
+            spec_dict = json.loads(as_string)
+    except Exception as e:
+        raise InvalidMetadataFile(f"Could not parse {path} due to: {e}") from e
+
+    # Ensure this version is not too new.
+    try:
+        layout_version = int(spec_dict.get("buildcache_layout_version", 0))
+    except ValueError as e:
+        raise InvalidMetadataFile("Could not parse layout version") from e
+
+    if layout_version > max_supported_layout:
+        raise InvalidMetadataFile(
+            f"Layout version {layout_version} is too new for this version of Spack"
+        )
+
+    return spec_dict, layout_version
+
+
 def download_tarball(spec, unsigned=False, mirrors_for_spec=None):
     """
     Download binary tarball for given package into stage area, returning
@@ -1502,8 +1636,6 @@ def download_tarball(spec, unsigned=False, mirrors_for_spec=None):
     tarball = tarball_path_name(spec, ".spack")
     specfile_prefix = tarball_name(spec, ".spec")
 
-    mirrors_to_try = []
-
     # Note on try_first and try_next:
     # mirrors_for_spec mostly likely came from spack caching remote
     # mirror indices locally and adding their specs to a local data
@@ -1516,63 +1648,140 @@ def download_tarball(spec, unsigned=False, mirrors_for_spec=None):
     try_first = [i["mirror_url"] for i in mirrors_for_spec] if mirrors_for_spec else []
     try_next = [i.fetch_url for i in configured_mirrors if i.fetch_url not in try_first]
 
-    for url in try_first + try_next:
-        mirrors_to_try.append(
-            {
-                "specfile": url_util.join(url, _build_cache_relative_path, specfile_prefix),
-                "spackfile": url_util.join(url, _build_cache_relative_path, tarball),
-            }
-        )
+    mirrors = try_first + try_next
 
     tried_to_verify_sigs = []
 
     # Assumes we care more about finding a spec file by preferred ext
     # than by mirrory priority.  This can be made less complicated as
     # we remove support for deprecated spec formats and buildcache layouts.
-    for ext in ["json.sig", "json"]:
-        for mirror_to_try in mirrors_to_try:
-            specfile_url = "{0}.{1}".format(mirror_to_try["specfile"], ext)
-            spackfile_url = mirror_to_try["spackfile"]
-            local_specfile_stage = try_fetch(specfile_url)
-            if local_specfile_stage:
-                local_specfile_path = local_specfile_stage.save_filename
-                signature_verified = False
+    for try_signed in (True, False):
+        for mirror in mirrors:
+            # If it's an OCI index, do things differently, since we cannot compose URLs.
+            parsed = urllib.parse.urlparse(mirror)
 
-                if ext.endswith(".sig") and not unsigned:
-                    # If we found a signed specfile at the root, try to verify
-                    # the signature immediately.  We will not download the
-                    # tarball if we could not verify the signature.
-                    tried_to_verify_sigs.append(specfile_url)
-                    signature_verified = try_verify(local_specfile_path)
-                    if not signature_verified:
-                        tty.warn("Failed to verify: {0}".format(specfile_url))
+            # TODO: refactor this to some "nice" place.
+            if parsed.scheme == "oci":
+                ref = spack.oci.image.ImageReference.from_string(mirror[len("oci://") :]).with_tag(
+                    spack.oci.image.default_tag(spec)
+                )
 
-                if unsigned or signature_verified or not ext.endswith(".sig"):
-                    # We will download the tarball in one of three cases:
-                    #     1. user asked for --no-check-signature
-                    #     2. user didn't ask for --no-check-signature, but we
-                    #     found a spec.json.sig and verified the signature already
-                    #     3. neither of the first two cases are true, but this file
-                    #     is *not* a signed json (not a spec.json.sig file).  That
-                    #     means we already looked at all the mirrors and either didn't
-                    #     find any .sig files or couldn't verify any of them.  But it
-                    #     is still possible to find an old style binary package where
-                    #     the signature is a detached .asc file in the outer archive
-                    #     of the tarball, and in that case, the only way to know is to
-                    #     download the tarball.  This is a deprecated use case, so if
-                    #     something goes wrong during the extraction process (can't
-                    #     verify signature, checksum doesn't match) we will fail at
-                    #     that point instead of trying to download more tarballs from
-                    #     the remaining mirrors, looking for one we can use.
-                    tarball_stage = try_fetch(spackfile_url)
-                    if tarball_stage:
-                        return {
-                            "tarball_stage": tarball_stage,
-                            "specfile_stage": local_specfile_stage,
-                            "signature_verified": signature_verified,
-                        }
+                # Fetch the manifest
+                try:
+                    response = spack.oci.opener.urlopen(
+                        urllib.request.Request(
+                            url=ref.manifest_url(),
+                            headers={"Accept": "application/vnd.oci.image.manifest.v1+json"},
+                        )
+                    )
+                except Exception:
+                    continue
 
-                local_specfile_stage.destroy()
+                # Download the config = spec.json and the relevant tarball
+                try:
+                    manifest = json.loads(response.read())
+                    spec_digest = spack.oci.image.Digest.from_string(manifest["config"]["digest"])
+                    tarball_digest = spack.oci.image.Digest.from_string(
+                        manifest["layers"][-1]["digest"]
+                    )
+                except Exception:
+                    continue
+
+                with spack.oci.oci.make_stage(
+                    ref.blob_url(spec_digest), spec_digest, keep=True
+                ) as local_specfile_stage:
+                    try:
+                        local_specfile_stage.fetch()
+                        local_specfile_stage.check()
+                        try:
+                            _get_valid_spec_file(
+                                local_specfile_stage.save_filename,
+                                CURRENT_BUILD_CACHE_LAYOUT_VERSION,
+                            )
+                        except InvalidMetadataFile as e:
+                            tty.warn(
+                                f"Ignoring binary package for {spec.name}/{spec.dag_hash()[:7]} "
+                                f"from {mirror} due to invalid metadata file: {e}"
+                            )
+                            local_specfile_stage.destroy()
+                            continue
+                    except Exception:
+                        continue
+                    local_specfile_stage.cache_local()
+
+                with spack.oci.oci.make_stage(
+                    ref.blob_url(tarball_digest), tarball_digest, keep=True
+                ) as tarball_stage:
+                    try:
+                        tarball_stage.fetch()
+                        tarball_stage.check()
+                    except Exception:
+                        continue
+                    tarball_stage.cache_local()
+
+                return {
+                    "tarball_stage": tarball_stage,
+                    "specfile_stage": local_specfile_stage,
+                    "signature_verified": False,
+                }
+
+            else:
+                ext = "json.sig" if try_signed else "json"
+                specfile_path = url_util.join(mirror, BUILD_CACHE_RELATIVE_PATH, specfile_prefix)
+                specfile_url = f"{specfile_path}.{ext}"
+                spackfile_url = url_util.join(mirror, BUILD_CACHE_RELATIVE_PATH, tarball)
+                local_specfile_stage = try_fetch(specfile_url)
+                if local_specfile_stage:
+                    local_specfile_path = local_specfile_stage.save_filename
+                    signature_verified = False
+
+                    try:
+                        _get_valid_spec_file(
+                            local_specfile_path, CURRENT_BUILD_CACHE_LAYOUT_VERSION
+                        )
+                    except InvalidMetadataFile as e:
+                        tty.warn(
+                            f"Ignoring binary package for {spec.name}/{spec.dag_hash()[:7]} "
+                            f"from {mirror} due to invalid metadata file: {e}"
+                        )
+                        local_specfile_stage.destroy()
+                        continue
+
+                    if try_signed and not unsigned:
+                        # If we found a signed specfile at the root, try to verify
+                        # the signature immediately.  We will not download the
+                        # tarball if we could not verify the signature.
+                        tried_to_verify_sigs.append(specfile_url)
+                        signature_verified = try_verify(local_specfile_path)
+                        if not signature_verified:
+                            tty.warn("Failed to verify: {0}".format(specfile_url))
+
+                    if unsigned or signature_verified or not try_signed:
+                        # We will download the tarball in one of three cases:
+                        #     1. user asked for --no-check-signature
+                        #     2. user didn't ask for --no-check-signature, but we
+                        #     found a spec.json.sig and verified the signature already
+                        #     3. neither of the first two cases are true, but this file
+                        #     is *not* a signed json (not a spec.json.sig file).  That
+                        #     means we already looked at all the mirrors and either didn't
+                        #     find any .sig files or couldn't verify any of them.  But it
+                        #     is still possible to find an old style binary package where
+                        #     the signature is a detached .asc file in the outer archive
+                        #     of the tarball, and in that case, the only way to know is to
+                        #     download the tarball.  This is a deprecated use case, so if
+                        #     something goes wrong during the extraction process (can't
+                        #     verify signature, checksum doesn't match) we will fail at
+                        #     that point instead of trying to download more tarballs from
+                        #     the remaining mirrors, looking for one we can use.
+                        tarball_stage = try_fetch(spackfile_url)
+                        if tarball_stage:
+                            return {
+                                "tarball_stage": tarball_stage,
+                                "specfile_stage": local_specfile_stage,
+                                "signature_verified": signature_verified,
+                            }
+
+                    local_specfile_stage.destroy()
 
     # Falling through the nested loops meeans we exhaustively searched
     # for all known kinds of spec files on all mirrors and did not find
@@ -1805,7 +2014,7 @@ def _extract_inner_tarball(spec, filename, extract_to, unsigned, remote_checksum
             )
 
     # compute the sha256 checksum of the tarball
-    local_checksum = checksum_tarball(tarfile_path)
+    local_checksum = spack.util.crypto.checksum(hashlib.sha256, tarfile_path)
     expected = remote_checksum["hash"]
 
     # if the checksums don't match don't install
@@ -1857,23 +2066,16 @@ def extract_tarball(spec, download_result, unsigned=False, force=False, timer=ti
     )
 
     specfile_path = download_result["specfile_stage"].save_filename
-
-    with open(specfile_path, "r") as inputfile:
-        content = inputfile.read()
-        if specfile_path.endswith(".json.sig"):
-            spec_dict = Spec.extract_json_from_clearsig(content)
-        else:
-            spec_dict = sjson.load(content)
-
+    spec_dict, layout_version = _get_valid_spec_file(
+        specfile_path, CURRENT_BUILD_CACHE_LAYOUT_VERSION
+    )
     bchecksum = spec_dict["binary_cache_checksum"]
+
     filename = download_result["tarball_stage"].save_filename
     signature_verified = download_result["signature_verified"]
     tmpdir = None
 
-    if (
-        "buildcache_layout_version" not in spec_dict
-        or int(spec_dict["buildcache_layout_version"]) < 1
-    ):
+    if layout_version == 0:
         # Handle the older buildcache layout where the .spack file
         # contains a spec json, maybe an .asc file (signature),
         # and another tarball containing the actual install tree.
@@ -1884,7 +2086,7 @@ def extract_tarball(spec, download_result, unsigned=False, force=False, timer=ti
             _delete_staged_downloads(download_result)
             shutil.rmtree(tmpdir)
             raise e
-    else:
+    elif layout_version == 1:
         # Newer buildcache layout: the .spack file contains just
         # in the install tree, the signature, if it exists, is
         # wrapped around the spec.json at the root.  If sig verify
@@ -1898,7 +2100,7 @@ def extract_tarball(spec, download_result, unsigned=False, force=False, timer=ti
             )
 
         # compute the sha256 checksum of the tarball
-        local_checksum = checksum_tarball(tarfile_path)
+        local_checksum = spack.util.crypto.checksum(hashlib.sha256, tarfile_path)
         expected = bchecksum["hash"]
 
         # if the checksums don't match don't install
@@ -1908,7 +2110,6 @@ def extract_tarball(spec, download_result, unsigned=False, force=False, timer=ti
             raise NoChecksumException(
                 tarfile_path, size, contents, "sha256", expected, local_checksum
             )
-
     try:
         with closing(tarfile.open(tarfile_path, "r")) as tar:
             # Remove install prefix from tarfil to extract directly into spec.prefix
@@ -2039,10 +2240,10 @@ def try_direct_fetch(spec, mirrors=None):
 
     for mirror in binary_mirrors:
         buildcache_fetch_url_json = url_util.join(
-            mirror.fetch_url, _build_cache_relative_path, specfile_name
+            mirror.fetch_url, BUILD_CACHE_RELATIVE_PATH, specfile_name
         )
         buildcache_fetch_url_signed_json = url_util.join(
-            mirror.fetch_url, _build_cache_relative_path, signed_specfile_name
+            mirror.fetch_url, BUILD_CACHE_RELATIVE_PATH, signed_specfile_name
         )
         try:
             _, _, fs = web_util.read_from_url(buildcache_fetch_url_signed_json)
@@ -2104,7 +2305,7 @@ def get_mirrors_for_spec(spec=None, mirrors_to_check=None, index_only=False):
         tty.debug("No Spack mirrors are currently configured")
         return {}
 
-    results = binary_index.find_built_spec(spec, mirrors_to_check=mirrors_to_check)
+    results = BINARY_INDEX.find_built_spec(spec, mirrors_to_check=mirrors_to_check)
 
     # The index may be out-of-date. If we aren't only considering indices, try
     # to fetch directly since we know where the file should be.
@@ -2113,7 +2314,7 @@ def get_mirrors_for_spec(spec=None, mirrors_to_check=None, index_only=False):
         # We found a spec by the direct fetch approach, we might as well
         # add it to our mapping.
         if results:
-            binary_index.update_spec(spec, results)
+            BINARY_INDEX.update_spec(spec, results)
 
     return results
 
@@ -2129,12 +2330,12 @@ def update_cache_and_get_specs():
     Throws:
         FetchCacheError
     """
-    binary_index.update()
-    return binary_index.get_all_built_specs()
+    BINARY_INDEX.update()
+    return BINARY_INDEX.get_all_built_specs()
 
 
 def clear_spec_cache():
-    binary_index.clear()
+    BINARY_INDEX.clear()
 
 
 def get_keys(install=False, trust=False, force=False, mirrors=None):
@@ -2147,7 +2348,7 @@ def get_keys(install=False, trust=False, force=False, mirrors=None):
     for mirror in mirror_collection.values():
         fetch_url = mirror.fetch_url
         keys_url = url_util.join(
-            fetch_url, _build_cache_relative_path, _build_cache_keys_relative_path
+            fetch_url, BUILD_CACHE_RELATIVE_PATH, BUILD_CACHE_KEYS_RELATIVE_PATH
         )
         keys_index = url_util.join(keys_url, "index.json")
 
@@ -2212,7 +2413,7 @@ def push_keys(*mirrors, **kwargs):
         for mirror in mirrors:
             push_url = getattr(mirror, "push_url", mirror)
             keys_url = url_util.join(
-                push_url, _build_cache_relative_path, _build_cache_keys_relative_path
+                push_url, BUILD_CACHE_RELATIVE_PATH, BUILD_CACHE_KEYS_RELATIVE_PATH
             )
             keys_local = url_util.local_file_path(keys_url)
 
@@ -2350,11 +2551,11 @@ def download_buildcache_entry(file_descriptions, mirror_url=None):
         )
 
     if mirror_url:
-        mirror_root = os.path.join(mirror_url, _build_cache_relative_path)
+        mirror_root = os.path.join(mirror_url, BUILD_CACHE_RELATIVE_PATH)
         return _download_buildcache_entry(mirror_root, file_descriptions)
 
     for mirror in spack.mirror.MirrorCollection(binary=True).values():
-        mirror_root = os.path.join(mirror.fetch_url, _build_cache_relative_path)
+        mirror_root = os.path.join(mirror.fetch_url, BUILD_CACHE_RELATIVE_PATH)
 
         if _download_buildcache_entry(mirror_root, file_descriptions):
             return True
@@ -2445,7 +2646,7 @@ def __init__(self, url, local_hash, urlopen=web_util.urlopen):
 
     def get_remote_hash(self):
         # Failure to fetch index.json.hash is not fatal
-        url_index_hash = url_util.join(self.url, _build_cache_relative_path, "index.json.hash")
+        url_index_hash = url_util.join(self.url, BUILD_CACHE_RELATIVE_PATH, "index.json.hash")
         try:
             response = self.urlopen(urllib.request.Request(url_index_hash, headers=self.headers))
         except urllib.error.URLError:
@@ -2457,7 +2658,7 @@ def get_remote_hash(self):
             return None
         return remote_hash.decode("utf-8")
 
-    def conditional_fetch(self):
+    def conditional_fetch(self) -> FetchIndexResult:
         # Do an intermediate fetch for the hash
         # and a conditional fetch for the contents
 
@@ -2466,17 +2667,17 @@ def conditional_fetch(self):
             return FetchIndexResult(etag=None, hash=None, data=None, fresh=True)
 
         # Otherwise, download index.json
-        url_index = url_util.join(self.url, _build_cache_relative_path, "index.json")
+        url_index = url_util.join(self.url, BUILD_CACHE_RELATIVE_PATH, "index.json")
 
         try:
             response = self.urlopen(urllib.request.Request(url_index, headers=self.headers))
         except urllib.error.URLError as e:
-            raise FetchIndexError("Could not fetch index from {}".format(url_index), e)
+            raise FetchIndexError("Could not fetch index from {}".format(url_index), e) from e
 
         try:
             result = codecs.getreader("utf-8")(response).read()
         except ValueError as e:
-            return FetchCacheError("Remote index {} is invalid".format(url_index), e)
+            raise FetchIndexError("Remote index {} is invalid".format(url_index), e) from e
 
         computed_hash = compute_hash(result)
 
@@ -2508,9 +2709,9 @@ def __init__(self, url, etag, urlopen=web_util.urlopen):
         self.etag = etag
         self.urlopen = urlopen
 
-    def conditional_fetch(self):
+    def conditional_fetch(self) -> FetchIndexResult:
         # Just do a conditional fetch immediately
-        url = url_util.join(self.url, _build_cache_relative_path, "index.json")
+        url = url_util.join(self.url, BUILD_CACHE_RELATIVE_PATH, "index.json")
         headers = {
             "User-Agent": web_util.SPACK_USER_AGENT,
             "If-None-Match": '"{}"'.format(self.etag),
@@ -2539,3 +2740,59 @@ def conditional_fetch(self):
             data=result,
             fresh=False,
         )
+
+
+class OCIIndexFetcher:
+    def __init__(self, url: str, local_hash, urlopen=None) -> None:
+        self.local_hash = local_hash
+
+        # Remove oci:// prefix
+        assert url.startswith("oci://")
+        self.ref = spack.oci.image.ImageReference.from_string(url[6:])
+        self.urlopen = urlopen or spack.oci.opener.urlopen
+
+    def conditional_fetch(self) -> FetchIndexResult:
+        """Download an index from an OCI registry type mirror."""
+        url_manifest = self.ref.with_tag(spack.oci.image.default_index_tag).manifest_url()
+        try:
+            response = self.urlopen(
+                urllib.request.Request(
+                    url=url_manifest,
+                    headers={"Accept": "application/vnd.oci.image.manifest.v1+json"},
+                )
+            )
+        except urllib.error.URLError as e:
+            raise FetchIndexError(
+                "Could not fetch manifest from {}".format(url_manifest), e
+            ) from e
+
+        try:
+            manifest = json.loads(response.read())
+        except Exception as e:
+            raise FetchIndexError("Remote index {} is invalid".format(url_manifest), e) from e
+
+        # Get first blob hash, which should be the index.json
+        try:
+            index_digest = spack.oci.image.Digest.from_string(manifest["layers"][0]["digest"])
+        except Exception as e:
+            raise FetchIndexError("Remote index {} is invalid".format(url_manifest), e) from e
+
+        # Fresh?
+        if index_digest.digest == self.local_hash:
+            return FetchIndexResult(etag=None, hash=None, data=None, fresh=True)
+
+        # Otherwise fetch the blob / index.json
+        response = self.urlopen(
+            urllib.request.Request(
+                url=self.ref.blob_url(index_digest),
+                headers={"Accept": "application/vnd.oci.image.layer.v1.tar+gzip"},
+            )
+        )
+
+        result = codecs.getreader("utf-8")(response).read()
+
+        # Make sure the blob we download has the advertised hash
+        if compute_hash(result) != index_digest.digest:
+            raise FetchIndexError(f"Remote index {url_manifest} is invalid")
+
+        return FetchIndexResult(etag=None, hash=index_digest.digest, data=result, fresh=False)

lib/spack/spack/bootstrap/config.py

@@ -143,7 +143,9 @@ def _bootstrap_config_scopes() -> Sequence["spack.config.ConfigScope"]:
 def _add_compilers_if_missing() -> None:
     arch = spack.spec.ArchSpec.frontend_arch()
     if not spack.compilers.compilers_for_arch(arch):
-        new_compilers = spack.compilers.find_new_compilers()
+        new_compilers = spack.compilers.find_new_compilers(
+            mixed_toolchain=sys.platform == "darwin"
+        )
         if new_compilers:
             spack.compilers.add_compilers_to_config(new_compilers, init_config=False)
 

lib/spack/spack/bootstrap/core.py

@@ -214,7 +214,7 @@ def _install_and_test(
         with spack.config.override(self.mirror_scope):
             # This index is currently needed to get the compiler used to build some
             # specs that we know by dag hash.
-            spack.binary_distribution.binary_index.regenerate_spec_cache()
+            spack.binary_distribution.BINARY_INDEX.regenerate_spec_cache()
             index = spack.binary_distribution.update_cache_and_get_specs()
 
             if not index:
@@ -291,6 +291,10 @@ def try_import(self, module: str, abstract_spec_str: str) -> bool:
         with spack_python_interpreter():
             # Add hint to use frontend operating system on Cray
             concrete_spec = spack.spec.Spec(abstract_spec_str + " ^" + spec_for_current_python())
+            # This is needed to help the old concretizer taking the `setuptools` dependency
+            # only when bootstrapping from sources on Python 3.12
+            if spec_for_current_python() == "python@3.12":
+                concrete_spec.constrain("+force_setuptools")
 
             if module == "clingo":
                 # TODO: remove when the old concretizer is deprecated  # pylint: disable=fixme

lib/spack/spack/build_environment.py

@@ -752,19 +752,13 @@ def setup_package(pkg, dirty, context: Context = Context.BUILD):
     target = platform.target(pkg.spec.architecture.target)
     platform.setup_platform_environment(pkg, env_mods)
 
-    if context == Context.BUILD:
-        tty.debug("setup_package: setup build environment for root")
-        builder = spack.builder.create(pkg)
-        builder.setup_build_environment(env_mods)
-
-        if (not dirty) and (not env_mods.is_unset("CPATH")):
-            tty.debug(
-                "A dependency has updated CPATH, this may lead pkg-"
-                "config to assume that the package is part of the system"
-                " includes and omit it when invoked with '--cflags'."
-            )
-    elif context == Context.TEST:
+    if context == Context.TEST:
         env_mods.prepend_path("PATH", ".")
+    elif context == Context.BUILD and not dirty and not env_mods.is_unset("CPATH"):
+        tty.debug(
+            "A dependency has updated CPATH, this may lead pkg-config to assume that the package "
+            "is part of the system includes and omit it when invoked with '--cflags'."
+        )
 
     # First apply the clean environment changes
     env_base.apply_modifications()
@@ -953,8 +947,11 @@ def __init__(self, *specs: spack.spec.Spec, context: Context) -> None:
             reversed(specs_with_type), lambda t: t[0].external
         )
         self.should_be_runnable = UseMode.BUILDTIME_DIRECT | UseMode.RUNTIME_EXECUTABLE
-        self.should_setup_run_env = UseMode.RUNTIME | UseMode.RUNTIME_EXECUTABLE
+        self.should_setup_run_env = (
+            UseMode.BUILDTIME_DIRECT | UseMode.RUNTIME | UseMode.RUNTIME_EXECUTABLE
+        )
         self.should_setup_dependent_build_env = UseMode.BUILDTIME | UseMode.BUILDTIME_DIRECT
+        self.should_setup_build_env = UseMode.ROOT if context == Context.BUILD else UseMode(0)
 
         if context == Context.RUN or context == Context.TEST:
             self.should_be_runnable |= UseMode.ROOT
@@ -994,8 +991,9 @@ def get_env_modifications(self) -> EnvironmentModifications:
         - Updating PATH for packages that are required at runtime
         - Updating CMAKE_PREFIX_PATH and PKG_CONFIG_PATH so that their respective
         tools can find Spack-built dependencies (when context=build)
-        - Running custom package environment modifications (setup_run_environment,
-        setup_dependent_build_environment, setup_dependent_run_environment)
+        - Running custom package environment modifications: setup_run_environment,
+        setup_dependent_run_environment, setup_build_environment,
+        setup_dependent_build_environment.
 
         The (partial) order imposed on the specs is externals first, then topological
         from leaf to root. That way externals cannot contribute search paths that would shadow
@@ -1008,19 +1006,27 @@ def get_env_modifications(self) -> EnvironmentModifications:
             if self.should_setup_dependent_build_env & flag:
                 self._make_buildtime_detectable(dspec, env)
 
-                for spec in self.specs:
-                    builder = spack.builder.create(pkg)
-                    builder.setup_dependent_build_environment(env, spec)
+                for root in self.specs:  # there is only one root in build context
+                    spack.builder.create(pkg).setup_dependent_build_environment(env, root)
+
+            if self.should_setup_build_env & flag:
+                spack.builder.create(pkg).setup_build_environment(env)
 
             if self.should_be_runnable & flag:
                 self._make_runnable(dspec, env)
 
             if self.should_setup_run_env & flag:
-                # TODO: remove setup_dependent_run_environment...
-                for spec in dspec.dependents(deptype=dt.RUN):
+                run_env_mods = EnvironmentModifications()
+                for spec in dspec.dependents(deptype=dt.LINK | dt.RUN):
                     if id(spec) in self.nodes_in_subdag:
-                        pkg.setup_dependent_run_environment(env, spec)
-                pkg.setup_run_environment(env)
+                        pkg.setup_dependent_run_environment(run_env_mods, spec)
+                pkg.setup_run_environment(run_env_mods)
+                if self.context == Context.BUILD:
+                    # Don't let the runtime environment of comiler like dependencies leak into the
+                    # build env
+                    run_env_mods.drop("CC", "CXX", "F77", "FC")
+                env.extend(run_env_mods)
+
         return env
 
     def _make_buildtime_detectable(self, dep: spack.spec.Spec, env: EnvironmentModifications):

lib/spack/spack/build_systems/oneapi.py

@@ -9,11 +9,10 @@
 import shutil
 from os.path import basename, dirname, isdir
 
-from llnl.util.filesystem import find_headers, find_libraries, join_path
+from llnl.util.filesystem import find_headers, find_libraries, join_path, mkdirp
 from llnl.util.link_tree import LinkTree
 
 from spack.directives import conflicts, variant
-from spack.package import mkdirp
 from spack.util.environment import EnvironmentModifications
 from spack.util.executable import Executable
 
@@ -212,3 +211,7 @@ def link_flags(self):
     @property
     def ld_flags(self):
         return "{0} {1}".format(self.search_flags, self.link_flags)
+
+
+#: Tuple of Intel math libraries, exported to packages
+INTEL_MATH_LIBRARIES = ("intel-mkl", "intel-oneapi-mkl", "intel-parallel-studio")

lib/spack/spack/build_systems/python.py

@@ -6,7 +6,6 @@
 import os
 import re
 import shutil
-import stat
 from typing import Optional
 
 import archspec
@@ -24,14 +23,29 @@
 import spack.spec
 import spack.store
 from spack.directives import build_system, depends_on, extends, maintainers
-from spack.error import NoHeadersError, NoLibrariesError, SpecError
+from spack.error import NoHeadersError, NoLibrariesError
 from spack.install_test import test_part
-from spack.util.executable import Executable
-from spack.version import Version
 
 from ._checks import BaseBuilder, execute_install_time_tests
 
 
+def _flatten_dict(dictionary):
+    """Iterable that yields KEY=VALUE paths through a dictionary.
+    Args:
+        dictionary: Possibly nested dictionary of arbitrary keys and values.
+    Yields:
+        A single path through the dictionary.
+    """
+    for key, item in dictionary.items():
+        if isinstance(item, dict):
+            # Recursive case
+            for value in _flatten_dict(item):
+                yield f"{key}={value}"
+        else:
+            # Base case
+            yield f"{key}={item}"
+
+
 class PythonExtension(spack.package_base.PackageBase):
     maintainers("adamjstewart")
 
@@ -353,51 +367,6 @@ def libs(self):
         raise NoLibrariesError(msg.format(self.spec.name, root))
 
 
-def fixup_shebangs(path: str, old_interpreter: bytes, new_interpreter: bytes):
-    # Recurse into the install prefix and fixup shebangs
-    exe = stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH
-    dirs = [path]
-    hardlinks = set()
-
-    while dirs:
-        with os.scandir(dirs.pop()) as entries:
-            for entry in entries:
-                if entry.is_dir(follow_symlinks=False):
-                    dirs.append(entry.path)
-                    continue
-
-                # Only consider files, not symlinks
-                if not entry.is_file(follow_symlinks=False):
-                    continue
-
-                lstat = entry.stat(follow_symlinks=False)
-
-                # Skip over files that are not executable
-                if not (lstat.st_mode & exe):
-                    continue
-
-                # Don't modify hardlinks more than once
-                if lstat.st_nlink > 1:
-                    key = (lstat.st_ino, lstat.st_dev)
-                    if key in hardlinks:
-                        continue
-                    hardlinks.add(key)
-
-                # Finally replace shebangs if any.
-                with open(entry.path, "rb+") as f:
-                    contents = f.read(2)
-                    if contents != b"#!":
-                        continue
-                    contents += f.read()
-
-                    if old_interpreter not in contents:
-                        continue
-
-                    f.seek(0)
-                    f.write(contents.replace(old_interpreter, new_interpreter))
-                    f.truncate()
-
-
 @spack.builder.builder("python_pip")
 class PythonPipBuilder(BaseBuilder):
     phases = ("install",)
@@ -409,7 +378,7 @@ class PythonPipBuilder(BaseBuilder):
     legacy_long_methods = ("install_options", "global_options", "config_settings")
 
     #: Names associated with package attributes in the old build-system format
-    legacy_attributes = ("build_directory", "install_time_test_callbacks")
+    legacy_attributes = ("archive_files", "build_directory", "install_time_test_callbacks")
 
     #: Callback names for install-time test
     install_time_test_callbacks = ["test"]
@@ -454,14 +423,15 @@ def build_directory(self):
     def config_settings(self, spec, prefix):
         """Configuration settings to be passed to the PEP 517 build backend.
 
-        Requires pip 22.1 or newer.
+        Requires pip 22.1 or newer for keys that appear only a single time,
+        or pip 23.1 or newer if the same key appears multiple times.
 
         Args:
             spec (spack.spec.Spec): build spec
             prefix (spack.util.prefix.Prefix): installation prefix
 
         Returns:
-            dict: dictionary of KEY, VALUE settings
+            dict: Possibly nested dictionary of KEY, VALUE settings
         """
         return {}
 
@@ -494,84 +464,32 @@ def global_options(self, spec, prefix):
         """
         return []
 
-    @property
-    def _build_venv_path(self):
-        """Return the path to the virtual environment used for building when
-        python is external."""
-        return os.path.join(self.spec.package.stage.path, "build_env")
-
-    @property
-    def _build_venv_python(self) -> Executable:
-        """Return the Python executable in the build virtual environment when
-        python is external."""
-        return Executable(os.path.join(self._build_venv_path, "bin", "python"))
-
     def install(self, pkg, spec, prefix):
         """Install everything from build directory."""
-        python: Executable = spec["python"].command
-        # Since we invoke pip with --no-build-isolation, we have to make sure that pip cannot
-        # execute hooks from user and system site-packages.
-        if spec["python"].external:
-            # There are no environment variables to disable the system site-packages, so we use a
-            # virtual environment instead. The downside of this approach is that pip produces
-            # incorrect shebangs that refer to the virtual environment, which we have to fix up.
-            python("-m", "venv", "--without-pip", self._build_venv_path)
-            pip = self._build_venv_python
-        else:
-            # For a Spack managed Python, system site-packages is empty/unused by design, so it
-            # suffices to disable user site-packages, for which there is an environment variable.
-            pip = python
-            pip.add_default_env("PYTHONNOUSERSITE", "1")
-        pip.add_default_arg("-m")
-        pip.add_default_arg("pip")
 
-        args = PythonPipBuilder.std_args(pkg) + ["--prefix=" + prefix]
-
-        for key, value in self.config_settings(spec, prefix).items():
-            if spec["py-pip"].version < Version("22.1"):
-                raise SpecError(
-                    "'{}' package uses 'config_settings' which is only supported by "
-                    "pip 22.1+. Add the following line to the package to fix this:\n\n"
-                    '    depends_on("py-pip@22.1:", type="build")'.format(spec.name)
-                )
-
-            args.append("--config-settings={}={}".format(key, value))
+        args = PythonPipBuilder.std_args(pkg) + [f"--prefix={prefix}"]
 
+        for setting in _flatten_dict(self.config_settings(spec, prefix)):
+            args.append(f"--config-settings={setting}")
         for option in self.install_options(spec, prefix):
-            args.append("--install-option=" + option)
+            args.append(f"--install-option={option}")
         for option in self.global_options(spec, prefix):
-            args.append("--global-option=" + option)
+            args.append(f"--global-option={option}")
 
         if pkg.stage.archive_file and pkg.stage.archive_file.endswith(".whl"):
             args.append(pkg.stage.archive_file)
         else:
             args.append(".")
 
+        pip = spec["python"].command
+        # Hide user packages, since we don't have build isolation. This is
+        # necessary because pip / setuptools may run hooks from arbitrary
+        # packages during the build. There is no equivalent variable to hide
+        # system packages, so this is not reliable for external Python.
+        pip.add_default_env("PYTHONNOUSERSITE", "1")
+        pip.add_default_arg("-m")
+        pip.add_default_arg("pip")
         with fs.working_dir(self.build_directory):
             pip(*args)
 
-    @spack.builder.run_after("install")
-    def fixup_shebangs_pointing_to_build(self):
-        """When installing a package using an external python, we use a temporary virtual
-        environment which improves build isolation. The downside is that pip produces shebangs
-        that point to the temporary virtual environment. This method fixes them up to point to the
-        underlying Python."""
-        # No need to fixup shebangs if no build venv was used. (this post install function also
-        # runs when install was overridden in another package, so check existence of the venv path)
-        if not os.path.exists(self._build_venv_path):
-            return
-
-        # Use sys.executable, since that's what pip uses.
-        interpreter = (
-            lambda python: python("-c", "import sys; print(sys.executable)", output=str)
-            .strip()
-            .encode("utf-8")
-        )
-
-        fixup_shebangs(
-            path=self.spec.prefix,
-            old_interpreter=interpreter(self._build_venv_python),
-            new_interpreter=interpreter(self.spec["python"].command),
-        )
-
     spack.builder.run_after("install")(execute_install_time_tests)

lib/spack/spack/ci.py

@@ -25,6 +25,7 @@
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 from llnl.util.lang import memoized
+from llnl.util.tty.color import cescape, colorize
 
 import spack
 import spack.binary_distribution as bindist
@@ -97,15 +98,6 @@ def _remove_reserved_tags(tags):
     return [tag for tag in tags if tag not in SPACK_RESERVED_TAGS]
 
 
-def _get_spec_string(spec):
-    format_elements = ["{name}{@version}", "{%compiler}"]
-
-    if spec.architecture:
-        format_elements.append(" {arch=architecture}")
-
-    return spec.format("".join(format_elements))
-
-
 def _spec_deps_key(s):
     return "{0}/{1}".format(s.name, s.dag_hash(7))
 
@@ -210,22 +202,22 @@ def _print_staging_summary(spec_labels, stages, mirrors_to_check, rebuild_decisi
 
     tty.msg("Staging summary ([x] means a job needs rebuilding):")
     for stage_index, stage in enumerate(stages):
-        tty.msg("  stage {0} ({1} jobs):".format(stage_index, len(stage)))
+        tty.msg(f"  stage {stage_index} ({len(stage)} jobs):")
 
-        for job in sorted(stage):
+        for job in sorted(stage, key=lambda j: (not rebuild_decisions[j].rebuild, j)):
             s = spec_labels[job]
-            rebuild = rebuild_decisions[job].rebuild
             reason = rebuild_decisions[job].reason
-            reason_msg = " ({0})".format(reason) if reason else ""
-            tty.msg(
-                "    [{1}] {0} -> {2}{3}".format(
-                    job, "x" if rebuild else " ", _get_spec_string(s), reason_msg
-                )
-            )
-            if rebuild_decisions[job].mirrors:
-                tty.msg("          found on the following mirrors:")
-                for murl in rebuild_decisions[job].mirrors:
-                    tty.msg("            {0}".format(murl))
+            reason_msg = f" ({reason})" if reason else ""
+            spec_fmt = "{name}{@version}{%compiler}{/hash:7}"
+            if rebuild_decisions[job].rebuild:
+                status = colorize("@*g{[x]}  ")
+                msg = f"  {status}{s.cformat(spec_fmt)}{reason_msg}"
+            else:
+                msg = f"{s.format(spec_fmt)}{reason_msg}"
+                if rebuild_decisions[job].mirrors:
+                    msg += f" [{', '.join(rebuild_decisions[job].mirrors)}]"
+                msg = colorize(f"  @K -   {cescape(msg)}@.")
+            tty.msg(msg)
 
 
 def _compute_spec_deps(spec_list):
@@ -932,7 +924,7 @@ def generate_gitlab_ci_yaml(
 
     # Speed up staging by first fetching binary indices from all mirrors
     try:
-        bindist.binary_index.update()
+        bindist.BINARY_INDEX.update()
     except bindist.FetchCacheError as e:
         tty.warn(e)
 
@@ -2258,13 +2250,13 @@ def build_name(self):
                 spec.architecture,
                 self.build_group,
             )
-            tty.verbose(
+            tty.debug(
                 "Generated CDash build name ({0}) from the {1}".format(build_name, spec.name)
             )
             return build_name
 
         build_name = os.environ.get("SPACK_CDASH_BUILD_NAME")
-        tty.verbose("Using CDash build name ({0}) from the environment".format(build_name))
+        tty.debug("Using CDash build name ({0}) from the environment".format(build_name))
         return build_name
 
     @property  # type: ignore
@@ -2278,11 +2270,11 @@ def build_stamp(self):
         Returns: (str) current CDash build stamp"""
         build_stamp = os.environ.get("SPACK_CDASH_BUILD_STAMP")
         if build_stamp:
-            tty.verbose("Using build stamp ({0}) from the environment".format(build_stamp))
+            tty.debug("Using build stamp ({0}) from the environment".format(build_stamp))
             return build_stamp
 
         build_stamp = cdash_build_stamp(self.build_group, time.time())
-        tty.verbose("Generated new build stamp ({0})".format(build_stamp))
+        tty.debug("Generated new build stamp ({0})".format(build_stamp))
         return build_stamp
 
     @property  # type: ignore

lib/spack/spack/cmd/buildcache.py

@@ -3,16 +3,19 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import argparse
+import copy
 import glob
+import hashlib
 import json
+import multiprocessing.pool
 import os
 import shutil
 import sys
 import tempfile
-from typing import List
+import urllib.request
+from typing import Dict, List, Optional, Tuple
 
 import llnl.util.tty as tty
-import llnl.util.tty.color as clr
 from llnl.string import plural
 from llnl.util.lang import elide_list
 
@@ -22,17 +25,37 @@
 import spack.config
 import spack.environment as ev
 import spack.error
+import spack.hash_types as ht
 import spack.mirror
+import spack.oci.oci
+import spack.oci.opener
 import spack.relocate
 import spack.repo
 import spack.spec
+import spack.stage
 import spack.store
+import spack.user_environment
 import spack.util.crypto
 import spack.util.url as url_util
 import spack.util.web as web_util
+from spack.build_environment import determine_number_of_jobs
 from spack.cmd import display_specs
+from spack.oci.image import (
+    Digest,
+    ImageReference,
+    default_config,
+    default_index_tag,
+    default_manifest,
+    default_tag,
+    tag_is_spec,
+)
+from spack.oci.oci import (
+    copy_missing_layers_with_retry,
+    get_manifest_and_config_with_retry,
+    upload_blob_with_retry,
+    upload_manifest_with_retry,
+)
 from spack.spec import Spec, save_dependency_specfiles
-from spack.stage import Stage
 
 description = "create, download and install binary packages"
 section = "packaging"
@@ -58,7 +81,9 @@ def setup_parser(subparser: argparse.ArgumentParser):
     push_sign.add_argument(
         "--key", "-k", metavar="key", type=str, default=None, help="key for signing"
     )
-    push.add_argument("mirror", type=str, help="mirror name, path, or URL")
+    push.add_argument(
+        "mirror", type=arguments.mirror_name_or_url, help="mirror name, path, or URL"
+    )
     push.add_argument(
         "--update-index",
         "--rebuild-index",
@@ -84,7 +109,10 @@ def setup_parser(subparser: argparse.ArgumentParser):
         action="store_true",
         help="stop pushing on first failure (default is best effort)",
     )
-    arguments.add_common_arguments(push, ["specs"])
+    push.add_argument(
+        "--base-image", default=None, help="specify the base image for the buildcache. "
+    )
+    arguments.add_common_arguments(push, ["specs", "jobs"])
     push.set_defaults(func=push_fn)
 
     install = subparsers.add_parser("install", help=install_fn.__doc__)
@@ -268,7 +296,22 @@ def _matching_specs(specs: List[Spec]) -> List[Spec]:
     return [spack.cmd.disambiguate_spec(s, ev.active_environment(), installed=any) for s in specs]
 
 
-def push_fn(args: argparse.Namespace):
+def _format_spec(spec: Spec) -> str:
+    return spec.cformat("{name}{@version}{/hash:7}")
+
+
+def _progress(i: int, total: int):
+    if total > 1:
+        digits = len(str(total))
+        return f"[{i+1:{digits}}/{total}] "
+    return ""
+
+
+def _make_pool():
+    return multiprocessing.pool.Pool(determine_number_of_jobs(parallel=True))
+
+
+def push_fn(args):
     """create a binary package and push it to a mirror"""
     if args.spec_file:
         tty.warn(
@@ -281,63 +324,80 @@ def push_fn(args: argparse.Namespace):
     else:
         specs = spack.cmd.require_active_env("buildcache push").all_specs()
 
-    mirror = arguments.mirror_name_or_url(args.mirror)
-
     if args.allow_root:
         tty.warn(
             "The flag `--allow-root` is the default in Spack 0.21, will be removed in Spack 0.22"
         )
 
-    url = mirror.push_url
+    # Check if this is an OCI image.
+    try:
+        image_ref = spack.oci.oci.image_from_mirror(args.mirror)
+    except ValueError:
+        image_ref = None
 
+    # For OCI images, we require dependencies to be pushed for now.
+    if image_ref:
+        if "dependencies" not in args.things_to_install:
+            tty.die("Dependencies must be pushed for OCI images.")
+        if not args.unsigned:
+            tty.warn(
+                "Code signing is currently not supported for OCI images. "
+                "Use --unsigned to silence this warning."
+            )
+
+    # This is a list of installed, non-external specs.
     specs = bindist.specs_to_be_packaged(
         specs,
         root="package" in args.things_to_install,
         dependencies="dependencies" in args.things_to_install,
     )
 
+    url = args.mirror.push_url
+
     # When pushing multiple specs, print the url once ahead of time, as well as how
     # many specs are being pushed.
     if len(specs) > 1:
         tty.info(f"Selected {len(specs)} specs to push to {url}")
 
-    skipped = []
     failed = []
 
-    # tty printing
-    color = clr.get_color_when()
-    format_spec = lambda s: s.format("{name}{@version}{/hash:7}", color=color)
-    total_specs = len(specs)
-    digits = len(str(total_specs))
+    # TODO: unify this logic in the future.
+    if image_ref:
+        with tempfile.TemporaryDirectory(
+            dir=spack.stage.get_stage_root()
+        ) as tmpdir, _make_pool() as pool:
+            skipped = _push_oci(args, image_ref, specs, tmpdir, pool)
+    else:
+        skipped = []
 
-    for i, spec in enumerate(specs):
-        try:
-            bindist.push_or_raise(
-                spec,
-                url,
-                bindist.PushOptions(
-                    force=args.force,
-                    unsigned=args.unsigned,
-                    key=args.key,
-                    regenerate_index=args.update_index,
-                ),
-            )
+        for i, spec in enumerate(specs):
+            try:
+                bindist.push_or_raise(
+                    spec,
+                    url,
+                    bindist.PushOptions(
+                        force=args.force,
+                        unsigned=args.unsigned,
+                        key=args.key,
+                        regenerate_index=args.update_index,
+                    ),
+                )
 
-            if total_specs > 1:
-                msg = f"[{i+1:{digits}}/{total_specs}] Pushed {format_spec(spec)}"
-            else:
-                msg = f"Pushed {format_spec(spec)} to {url}"
+                msg = f"{_progress(i, len(specs))}Pushed {_format_spec(spec)}"
+                if len(specs) == 1:
+                    msg += f" to {url}"
+                tty.info(msg)
 
-            tty.info(msg)
+            except bindist.NoOverwriteException:
+                skipped.append(_format_spec(spec))
 
-        except bindist.NoOverwriteException:
-            skipped.append(format_spec(spec))
-
-        # Catch any other exception unless the fail fast option is set
-        except Exception as e:
-            if args.fail_fast or isinstance(e, (bindist.PickKeyException, bindist.NoKeyException)):
-                raise
-            failed.append((format_spec(spec), e))
+            # Catch any other exception unless the fail fast option is set
+            except Exception as e:
+                if args.fail_fast or isinstance(
+                    e, (bindist.PickKeyException, bindist.NoKeyException)
+                ):
+                    raise
+                failed.append((_format_spec(spec), e))
 
     if skipped:
         if len(specs) == 1:
@@ -364,6 +424,341 @@ def push_fn(args: argparse.Namespace):
             ),
         )
 
+    # Update the index if requested
+    # TODO: remove update index logic out of bindist; should be once after all specs are pushed
+    # not once per spec.
+    if image_ref and len(skipped) < len(specs) and args.update_index:
+        with tempfile.TemporaryDirectory(
+            dir=spack.stage.get_stage_root()
+        ) as tmpdir, _make_pool() as pool:
+            _update_index_oci(image_ref, tmpdir, pool)
+
+
+def _get_spack_binary_blob(image_ref: ImageReference) -> Optional[spack.oci.oci.Blob]:
+    """Get the spack tarball layer digests and size if it exists"""
+    try:
+        manifest, config = get_manifest_and_config_with_retry(image_ref)
+
+        return spack.oci.oci.Blob(
+            compressed_digest=Digest.from_string(manifest["layers"][-1]["digest"]),
+            uncompressed_digest=Digest.from_string(config["rootfs"]["diff_ids"][-1]),
+            size=manifest["layers"][-1]["size"],
+        )
+    except Exception:
+        return None
+
+
+def _push_single_spack_binary_blob(image_ref: ImageReference, spec: spack.spec.Spec, tmpdir: str):
+    filename = os.path.join(tmpdir, f"{spec.dag_hash()}.tar.gz")
+
+    # Create an oci.image.layer aka tarball of the package
+    compressed_tarfile_checksum, tarfile_checksum = spack.oci.oci.create_tarball(spec, filename)
+
+    blob = spack.oci.oci.Blob(
+        Digest.from_sha256(compressed_tarfile_checksum),
+        Digest.from_sha256(tarfile_checksum),
+        os.path.getsize(filename),
+    )
+
+    # Upload the blob
+    upload_blob_with_retry(image_ref, file=filename, digest=blob.compressed_digest)
+
+    # delete the file
+    os.unlink(filename)
+
+    return blob
+
+
+def _retrieve_env_dict_from_config(config: dict) -> dict:
+    """Retrieve the environment variables from the image config file.
+    Sets a default value for PATH if it is not present.
+
+    Args:
+        config (dict): The image config file.
+
+    Returns:
+        dict: The environment variables.
+    """
+    env = {"PATH": "/bin:/usr/bin"}
+
+    if "Env" in config.get("config", {}):
+        for entry in config["config"]["Env"]:
+            key, value = entry.split("=", 1)
+            env[key] = value
+    return env
+
+
+def _archspec_to_gooarch(spec: spack.spec.Spec) -> str:
+    name = spec.target.family.name
+    name_map = {"aarch64": "arm64", "x86_64": "amd64"}
+    return name_map.get(name, name)
+
+
+def _put_manifest(
+    base_images: Dict[str, Tuple[dict, dict]],
+    checksums: Dict[str, spack.oci.oci.Blob],
+    spec: spack.spec.Spec,
+    image_ref: ImageReference,
+    tmpdir: str,
+):
+    architecture = _archspec_to_gooarch(spec)
+
+    dependencies = list(
+        reversed(
+            list(
+                s
+                for s in spec.traverse(order="topo", deptype=("link", "run"), root=True)
+                if not s.external
+            )
+        )
+    )
+
+    base_manifest, base_config = base_images[architecture]
+    env = _retrieve_env_dict_from_config(base_config)
+
+    spack.user_environment.environment_modifications_for_specs(spec).apply_modifications(env)
+
+    # Create an oci.image.config file
+    config = copy.deepcopy(base_config)
+
+    # Add the diff ids of the dependencies
+    for s in dependencies:
+        config["rootfs"]["diff_ids"].append(str(checksums[s.dag_hash()].uncompressed_digest))
+
+    # Set the environment variables
+    config["config"]["Env"] = [f"{k}={v}" for k, v in env.items()]
+
+    # From the OCI v1.0 spec:
+    # > Any extra fields in the Image JSON struct are considered implementation
+    # > specific and MUST be ignored by any implementations which are unable to
+    # > interpret them.
+    # We use this to store the Spack spec, so we can use it to create an index.
+    spec_dict = spec.to_dict(hash=ht.dag_hash)
+    spec_dict["buildcache_layout_version"] = 1
+    spec_dict["binary_cache_checksum"] = {
+        "hash_algorithm": "sha256",
+        "hash": checksums[spec.dag_hash()].compressed_digest.digest,
+    }
+    config.update(spec_dict)
+
+    config_file = os.path.join(tmpdir, f"{spec.dag_hash()}.config.json")
+
+    with open(config_file, "w") as f:
+        json.dump(config, f, separators=(",", ":"))
+
+    config_file_checksum = Digest.from_sha256(
+        spack.util.crypto.checksum(hashlib.sha256, config_file)
+    )
+
+    # Upload the config file
+    upload_blob_with_retry(image_ref, file=config_file, digest=config_file_checksum)
+
+    oci_manifest = {
+        "mediaType": "application/vnd.oci.image.manifest.v1+json",
+        "schemaVersion": 2,
+        "config": {
+            "mediaType": base_manifest["config"]["mediaType"],
+            "digest": str(config_file_checksum),
+            "size": os.path.getsize(config_file),
+        },
+        "layers": [
+            *(layer for layer in base_manifest["layers"]),
+            *(
+                {
+                    "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
+                    "digest": str(checksums[s.dag_hash()].compressed_digest),
+                    "size": checksums[s.dag_hash()].size,
+                }
+                for s in dependencies
+            ),
+        ],
+        "annotations": {"org.opencontainers.image.description": spec.format()},
+    }
+
+    image_ref_for_spec = image_ref.with_tag(default_tag(spec))
+
+    # Finally upload the manifest
+    upload_manifest_with_retry(image_ref_for_spec, oci_manifest=oci_manifest)
+
+    # delete the config file
+    os.unlink(config_file)
+
+    return image_ref_for_spec
+
+
+def _push_oci(
+    args,
+    image_ref: ImageReference,
+    installed_specs_with_deps: List[Spec],
+    tmpdir: str,
+    pool: multiprocessing.pool.Pool,
+) -> List[str]:
+    """Push specs to an OCI registry
+
+    Args:
+        args: The command line arguments.
+        image_ref: The image reference.
+        installed_specs_with_deps: The installed specs to push, excluding externals,
+            including deps, ordered from roots to leaves.
+
+    Returns:
+        List[str]: The list of skipped specs (already in the buildcache).
+    """
+
+    # Reverse the order
+    installed_specs_with_deps = list(reversed(installed_specs_with_deps))
+
+    # The base image to use for the package. When not set, we use
+    # the OCI registry only for storage, and do not use any base image.
+    base_image_ref: Optional[ImageReference] = (
+        ImageReference.from_string(args.base_image) if args.base_image else None
+    )
+
+    # Spec dag hash -> blob
+    checksums: Dict[str, spack.oci.oci.Blob] = {}
+
+    # arch -> (manifest, config)
+    base_images: Dict[str, Tuple[dict, dict]] = {}
+
+    # Specs not uploaded because they already exist
+    skipped = []
+
+    if not args.force:
+        tty.info("Checking for existing specs in the buildcache")
+        to_be_uploaded = []
+
+        tags_to_check = (image_ref.with_tag(default_tag(s)) for s in installed_specs_with_deps)
+        available_blobs = pool.map(_get_spack_binary_blob, tags_to_check)
+
+        for spec, maybe_blob in zip(installed_specs_with_deps, available_blobs):
+            if maybe_blob is not None:
+                checksums[spec.dag_hash()] = maybe_blob
+                skipped.append(_format_spec(spec))
+            else:
+                to_be_uploaded.append(spec)
+    else:
+        to_be_uploaded = installed_specs_with_deps
+
+    if not to_be_uploaded:
+        return skipped
+
+    tty.info(
+        f"{len(to_be_uploaded)} specs need to be pushed to {image_ref.domain}/{image_ref.name}"
+    )
+
+    # Upload blobs
+    new_blobs = pool.starmap(
+        _push_single_spack_binary_blob, ((image_ref, spec, tmpdir) for spec in to_be_uploaded)
+    )
+
+    # And update the spec to blob mapping
+    for spec, blob in zip(to_be_uploaded, new_blobs):
+        checksums[spec.dag_hash()] = blob
+
+    # Copy base image layers, probably fine to do sequentially.
+    for spec in to_be_uploaded:
+        architecture = _archspec_to_gooarch(spec)
+        # Get base image details, if we don't have them yet
+        if architecture in base_images:
+            continue
+        if base_image_ref is None:
+            base_images[architecture] = (default_manifest(), default_config(architecture, "linux"))
+        else:
+            base_images[architecture] = copy_missing_layers_with_retry(
+                base_image_ref, image_ref, architecture
+            )
+
+    # Upload manifests
+    tty.info("Uploading manifests")
+    pushed_image_ref = pool.starmap(
+        _put_manifest,
+        ((base_images, checksums, spec, image_ref, tmpdir) for spec in to_be_uploaded),
+    )
+
+    # Print the image names of the top-level specs
+    for spec, ref in zip(to_be_uploaded, pushed_image_ref):
+        tty.info(f"Pushed {_format_spec(spec)} to {ref}")
+
+    return skipped
+
+
+def _config_from_tag(image_ref: ImageReference, tag: str) -> Optional[dict]:
+    # Don't allow recursion here, since Spack itself always uploads
+    # vnd.oci.image.manifest.v1+json, not vnd.oci.image.index.v1+json
+    _, config = get_manifest_and_config_with_retry(image_ref.with_tag(tag), tag, recurse=0)
+
+    # Do very basic validation: if "spec" is a key in the config, it
+    # must be a Spec object too.
+    return config if "spec" in config else None
+
+
+def _update_index_oci(
+    image_ref: ImageReference, tmpdir: str, pool: multiprocessing.pool.Pool
+) -> None:
+    response = spack.oci.opener.urlopen(urllib.request.Request(url=image_ref.tags_url()))
+    spack.oci.opener.ensure_status(response, 200)
+    tags = json.load(response)["tags"]
+
+    # Fetch all image config files in parallel
+    spec_dicts = pool.starmap(
+        _config_from_tag, ((image_ref, tag) for tag in tags if tag_is_spec(tag))
+    )
+
+    # Populate the database
+    db_root_dir = os.path.join(tmpdir, "db_root")
+    db = bindist.BuildCacheDatabase(db_root_dir)
+
+    for spec_dict in spec_dicts:
+        spec = Spec.from_dict(spec_dict)
+        db.add(spec, directory_layout=None)
+        db.mark(spec, "in_buildcache", True)
+
+    # Create the index.json file
+    index_json_path = os.path.join(tmpdir, "index.json")
+    with open(index_json_path, "w") as f:
+        db._write_to_file(f)
+
+    # Create an empty config.json file
+    empty_config_json_path = os.path.join(tmpdir, "config.json")
+    with open(empty_config_json_path, "wb") as f:
+        f.write(b"{}")
+
+    # Upload the index.json file
+    index_shasum = Digest.from_sha256(spack.util.crypto.checksum(hashlib.sha256, index_json_path))
+    upload_blob_with_retry(image_ref, file=index_json_path, digest=index_shasum)
+
+    # Upload the config.json file
+    empty_config_digest = Digest.from_sha256(
+        spack.util.crypto.checksum(hashlib.sha256, empty_config_json_path)
+    )
+    upload_blob_with_retry(image_ref, file=empty_config_json_path, digest=empty_config_digest)
+
+    # Push a manifest file that references the index.json file as a layer
+    # Notice that we push this as if it is an image, which it of course is not.
+    # When the ORAS spec becomes official, we can use that instead of a fake image.
+    # For now we just use the OCI image spec, so that we don't run into issues with
+    # automatic garbage collection of blobs that are not referenced by any image manifest.
+    oci_manifest = {
+        "mediaType": "application/vnd.oci.image.manifest.v1+json",
+        "schemaVersion": 2,
+        # Config is just an empty {} file for now, and irrelevant
+        "config": {
+            "mediaType": "application/vnd.oci.image.config.v1+json",
+            "digest": str(empty_config_digest),
+            "size": os.path.getsize(empty_config_json_path),
+        },
+        # The buildcache index is the only layer, and is not a tarball, we lie here.
+        "layers": [
+            {
+                "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
+                "digest": str(index_shasum),
+                "size": os.path.getsize(index_json_path),
+            }
+        ],
+    }
+
+    upload_manifest_with_retry(image_ref.with_tag(default_index_tag), oci_manifest)
+
 
 def install_fn(args):
     """install from a binary package"""
@@ -522,7 +917,7 @@ def copy_buildcache_file(src_url, dest_url, local_path=None):
         local_path = os.path.join(tmpdir, os.path.basename(src_url))
 
     try:
-        temp_stage = Stage(src_url, path=os.path.dirname(local_path))
+        temp_stage = spack.stage.Stage(src_url, path=os.path.dirname(local_path))
         try:
             temp_stage.create()
             temp_stage.fetch()
@@ -616,6 +1011,20 @@ def manifest_copy(manifest_file_list):
 
 
 def update_index(mirror: spack.mirror.Mirror, update_keys=False):
+    # Special case OCI images for now.
+    try:
+        image_ref = spack.oci.oci.image_from_mirror(mirror)
+    except ValueError:
+        image_ref = None
+
+    if image_ref:
+        with tempfile.TemporaryDirectory(
+            dir=spack.stage.get_stage_root()
+        ) as tmpdir, _make_pool() as pool:
+            _update_index_oci(image_ref, tmpdir, pool)
+        return
+
+    # Otherwise, assume a normal mirror.
     url = mirror.push_url
 
     bindist.generate_package_index(url_util.join(url, bindist.build_cache_relative_path()))

lib/spack/spack/cmd/checksum.py

@@ -3,7 +3,6 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
-import argparse
 import re
 import sys
 
@@ -21,7 +20,6 @@
 from spack.package_base import PackageBase, deprecated_version, preferred_version
 from spack.util.editor import editor
 from spack.util.format import get_version_lines
-from spack.util.naming import valid_fully_qualified_module_name
 from spack.version import Version
 
 description = "checksum available versions of a package"
@@ -37,30 +35,30 @@ def setup_parser(subparser):
         help="don't clean up staging area when command completes",
     )
     subparser.add_argument(
-        "-b",
         "--batch",
+        "-b",
         action="store_true",
         default=False,
         help="don't ask which versions to checksum",
     )
     subparser.add_argument(
-        "-l",
         "--latest",
+        "-l",
         action="store_true",
         default=False,
         help="checksum the latest available version",
     )
     subparser.add_argument(
-        "-p",
         "--preferred",
+        "-p",
         action="store_true",
         default=False,
         help="checksum the known Spack preferred version",
     )
     modes_parser = subparser.add_mutually_exclusive_group()
     modes_parser.add_argument(
-        "-a",
         "--add-to-package",
+        "-a",
         action="store_true",
         default=False,
         help="add new versions to package",
@@ -68,27 +66,26 @@ def setup_parser(subparser):
     modes_parser.add_argument(
         "--verify", action="store_true", default=False, help="verify known package checksums"
     )
-    arguments.add_common_arguments(subparser, ["package", "jobs"])
+    subparser.add_argument("package", help="name or spec (e.g. `cmake` or `cmake@3.18`)")
     subparser.add_argument(
-        "versions", nargs=argparse.REMAINDER, help="versions to generate checksums for"
+        "versions",
+        nargs="*",
+        help="checksum these specific versions (if omitted, Spack searches for remote versions)",
+    )
+    arguments.add_common_arguments(subparser, ["jobs"])
+    subparser.epilog = (
+        "examples:\n"
+        "  `spack checksum zlib@1.2` autodetects versions 1.2.0 to 1.2.13 from the remote\n"
+        "  `spack checksum zlib 1.2.13` checksums exact version 1.2.13 directly without search\n"
     )
 
 
 def checksum(parser, args):
-    # Did the user pass 'package@version' string?
-    if len(args.versions) == 0 and "@" in args.package:
-        args.versions = [args.package.split("@")[1]]
-        args.package = args.package.split("@")[0]
-
-    # Make sure the user provided a package and not a URL
-    if not valid_fully_qualified_module_name(args.package):
-        tty.die("`spack checksum` accepts package names, not URLs.")
+    spec = spack.spec.Spec(args.package)
 
     # Get the package we're going to generate checksums for
-    pkg_cls = spack.repo.PATH.get_pkg_class(args.package)
-    pkg = pkg_cls(spack.spec.Spec(args.package))
+    pkg = spack.repo.PATH.get_pkg_class(spec.name)(spec)
 
-    # Build a list of versions to checksum
     versions = [Version(v) for v in args.versions]
 
     # Define placeholder for remote versions.
@@ -152,7 +149,10 @@ def checksum(parser, args):
         tty.die(f"Could not find any remote versions for {pkg.name}")
     elif len(url_dict) > 1 and not args.batch and sys.stdin.isatty():
         filtered_url_dict = spack.stage.interactive_version_filter(
-            url_dict, pkg.versions, url_changes=url_changed_for_version
+            url_dict,
+            pkg.versions,
+            url_changes=url_changed_for_version,
+            initial_verion_filter=spec.versions,
         )
         if not filtered_url_dict:
             exit(0)

lib/spack/spack/cmd/commands.py

@@ -796,7 +796,9 @@ def names(args: Namespace, out: IO) -> None:
     commands = copy.copy(spack.cmd.all_commands())
 
     if args.aliases:
-        commands.extend(spack.main.aliases.keys())
+        aliases = spack.config.get("config:aliases")
+        if aliases:
+            commands.extend(aliases.keys())
 
     colify(commands, output=out)
 
@@ -812,8 +814,10 @@ def bash(args: Namespace, out: IO) -> None:
     parser = spack.main.make_argument_parser()
     spack.main.add_all_commands(parser)
 
-    aliases = ";".join(f"{key}:{val}" for key, val in spack.main.aliases.items())
-    out.write(f'SPACK_ALIASES="{aliases}"\n\n')
+    aliases_config = spack.config.get("config:aliases")
+    if aliases_config:
+        aliases = ";".join(f"{key}:{val}" for key, val in aliases_config.items())
+        out.write(f'SPACK_ALIASES="{aliases}"\n\n')
 
     writer = BashCompletionWriter(parser.prog, out, args.aliases)
     writer.write(parser)

lib/spack/spack/cmd/common/arguments.py

@@ -543,7 +543,7 @@ def add_concretizer_args(subparser):
     )
 
 
-def add_s3_connection_args(subparser, add_help):
+def add_connection_args(subparser, add_help):
     subparser.add_argument(
         "--s3-access-key-id", help="ID string to use to connect to this S3 mirror"
     )
@@ -559,6 +559,8 @@ def add_s3_connection_args(subparser, add_help):
     subparser.add_argument(
         "--s3-endpoint-url", help="endpoint URL to use to connect to this S3 mirror"
     )
+    subparser.add_argument("--oci-username", help="username to use to connect to this OCI mirror")
+    subparser.add_argument("--oci-password", help="password to use to connect to this OCI mirror")
 
 
 def use_buildcache(cli_arg_value):

lib/spack/spack/cmd/common/confirmation.py

@@ -0,0 +1,30 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import sys
+from typing import List
+
+import llnl.util.tty as tty
+
+import spack.cmd
+
+display_args = {"long": True, "show_flags": False, "variants": False, "indent": 4}
+
+
+def confirm_action(specs: List[spack.spec.Spec], participle: str, noun: str):
+    """Display the list of specs to be acted on and ask for confirmation.
+
+    Args:
+        specs: specs to be removed
+        participle: action expressed as a participle, e.g. "uninstalled"
+        noun: action expressed as a noun, e.g. "uninstallation"
+    """
+    tty.msg(f"The following {len(specs)} packages will be {participle}:\n")
+    spack.cmd.display_specs(specs, **display_args)
+    print("")
+    answer = tty.get_yes_or_no("Do you want to proceed?", default=False)
+    if not answer:
+        tty.msg(f"Aborting {noun}")
+        sys.exit(0)

lib/spack/spack/cmd/compiler.py

@@ -31,6 +31,19 @@ def setup_parser(subparser):
         aliases=["add"],
         help="search the system for compilers to add to Spack configuration",
     )
+    mixed_toolchain_group = find_parser.add_mutually_exclusive_group()
+    mixed_toolchain_group.add_argument(
+        "--mixed-toolchain",
+        action="store_true",
+        default=sys.platform == "darwin",
+        help="Allow mixed toolchains (for example: clang, clang++, gfortran)",
+    )
+    mixed_toolchain_group.add_argument(
+        "--no-mixed-toolchain",
+        action="store_false",
+        dest="mixed_toolchain",
+        help="Do not allow mixed toolchains (for example: clang, clang++, gfortran)",
+    )
     find_parser.add_argument("add_paths", nargs=argparse.REMAINDER)
     find_parser.add_argument(
         "--scope",
@@ -86,7 +99,9 @@ def compiler_find(args):
 
     # Below scope=None because we want new compilers that don't appear
     # in any other configuration.
-    new_compilers = spack.compilers.find_new_compilers(paths, scope=None)
+    new_compilers = spack.compilers.find_new_compilers(
+        paths, scope=None, mixed_toolchain=args.mixed_toolchain
+    )
     if new_compilers:
         spack.compilers.add_compilers_to_config(new_compilers, scope=args.scope, init_config=False)
         n = len(new_compilers)

lib/spack/spack/cmd/config.py

@@ -407,7 +407,9 @@ def config_prefer_upstream(args):
     pkgs = {}
     for spec in pref_specs:
         # Collect all the upstream compilers and versions for this package.
-        pkg = pkgs.get(spec.name, {"version": [], "compiler": []})
+        pkg = pkgs.get(spec.name, {"version": []})
+        all = pkgs.get("all", {"compiler": []})
+        pkgs["all"] = all
         pkgs[spec.name] = pkg
 
         # We have no existing variant if this is our first added version.
@@ -418,8 +420,8 @@ def config_prefer_upstream(args):
             pkg["version"].append(version)
 
         compiler = str(spec.compiler)
-        if compiler not in pkg["compiler"]:
-            pkg["compiler"].append(compiler)
+        if compiler not in all["compiler"]:
+            all["compiler"].append(compiler)
 
         # Get and list all the variants that differ from the default.
         variants = []

lib/spack/spack/cmd/create.py

@@ -64,6 +64,7 @@ class {class_name}({base_class_name}):
     # maintainers("github_user1", "github_user2")
 
     # FIXME: Add the SPDX identifier of the project's license below.
+    # See https://spdx.org/licenses/ for a list.
     license("UNKNOWN")
 
 {versions}

lib/spack/spack/cmd/deconcretize.py

@@ -0,0 +1,103 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import argparse
+import sys
+from typing import List
+
+import llnl.util.tty as tty
+
+import spack.cmd
+import spack.cmd.common.arguments as arguments
+import spack.cmd.common.confirmation as confirmation
+import spack.environment as ev
+import spack.spec
+
+description = "remove specs from the concretized lockfile of an environment"
+section = "environments"
+level = "long"
+
+# Arguments for display_specs when we find ambiguity
+display_args = {"long": True, "show_flags": False, "variants": False, "indent": 4}
+
+
+def setup_parser(subparser):
+    subparser.add_argument(
+        "--root", action="store_true", help="deconcretize only specific environment roots"
+    )
+    arguments.add_common_arguments(subparser, ["yes_to_all", "specs"])
+    subparser.add_argument(
+        "-a",
+        "--all",
+        action="store_true",
+        dest="all",
+        help="deconcretize ALL specs that match each supplied spec",
+    )
+
+
+def get_deconcretize_list(
+    args: argparse.Namespace, specs: List[spack.spec.Spec], env: ev.Environment
+) -> List[spack.spec.Spec]:
+    """
+    Get list of environment roots to deconcretize
+    """
+    env_specs = [s for _, s in env.concretized_specs()]
+    to_deconcretize = []
+    errors = []
+
+    for s in specs:
+        if args.root:
+            # find all roots matching given spec
+            to_deconc = [e for e in env_specs if e.satisfies(s)]
+        else:
+            # find all roots matching or depending on a matching spec
+            to_deconc = [e for e in env_specs if any(d.satisfies(s) for d in e.traverse())]
+
+        if len(to_deconc) < 1:
+            tty.warn(f"No matching specs to deconcretize for {s}")
+
+        elif len(to_deconc) > 1 and not args.all:
+            errors.append((s, to_deconc))
+
+        to_deconcretize.extend(to_deconc)
+
+    if errors:
+        for spec, matching in errors:
+            tty.error(f"{spec} matches multiple concrete specs:")
+            sys.stderr.write("\n")
+            spack.cmd.display_specs(matching, output=sys.stderr, **display_args)
+            sys.stderr.write("\n")
+            sys.stderr.flush()
+        tty.die("Use '--all' to deconcretize all matching specs, or be more specific")
+
+    return to_deconcretize
+
+
+def deconcretize_specs(args, specs):
+    env = spack.cmd.require_active_env(cmd_name="deconcretize")
+
+    if args.specs:
+        deconcretize_list = get_deconcretize_list(args, specs, env)
+    else:
+        deconcretize_list = [s for _, s in env.concretized_specs()]
+
+    if not args.yes_to_all:
+        confirmation.confirm_action(deconcretize_list, "deconcretized", "deconcretization")
+
+    with env.write_transaction():
+        for spec in deconcretize_list:
+            env.deconcretize(spec)
+        env.write()
+
+
+def deconcretize(parser, args):
+    if not args.specs and not args.all:
+        tty.die(
+            "deconcretize requires at least one spec argument.",
+            " Use `spack deconcretize --all` to deconcretize ALL specs.",
+        )
+
+    specs = spack.cmd.parse_specs(args.specs) if args.specs else [any]
+    deconcretize_specs(args, specs)

lib/spack/spack/cmd/dev_build.py

@@ -99,10 +99,7 @@ def dev_build(self, args):
 
     spec = specs[0]
     if not spack.repo.PATH.exists(spec.name):
-        tty.die(
-            "No package for '{0}' was found.".format(spec.name),
-            "  Use `spack create` to create a new package",
-        )
+        raise spack.repo.UnknownPackageError(spec.name)
 
     if not spec.versions.concrete_range_as_version:
         tty.die(

lib/spack/spack/cmd/edit.py

@@ -43,10 +43,7 @@ def edit_package(name, repo_path, namespace):
         if not os.access(path, os.R_OK):
             tty.die("Insufficient permissions on '%s'!" % path)
     else:
-        tty.die(
-            "No package for '{0}' was found.".format(spec.name),
-            "  Use `spack create` to create a new package",
-        )
+        raise spack.repo.UnknownPackageError(spec.name)
 
     editor(path)
 

lib/spack/spack/cmd/env.py

@@ -5,6 +5,7 @@
 
 import argparse
 import os
+import shlex
 import shutil
 import sys
 import tempfile
@@ -144,10 +145,13 @@ def create_temp_env_directory():
     return tempfile.mkdtemp(prefix="spack-")
 
 
-def env_activate(args):
-    if not args.activate_env and not args.dir and not args.temp:
-        tty.die("spack env activate requires an environment name, directory, or --temp")
+def _tty_info(msg):
+    """tty.info like function that prints the equivalent printf statement for eval."""
+    decorated = f'{colorize("@*b{==>}")} {msg}\n'
+    print(f"printf {shlex.quote(decorated)};")
 
+
+def env_activate(args):
     if not args.shell:
         spack.cmd.common.shell_init_instructions(
             "spack env activate", "    eval `spack env activate {sh_arg} [...]`"
@@ -160,12 +164,25 @@ def env_activate(args):
 
     env_name_or_dir = args.activate_env or args.dir
 
+    # When executing `spack env activate` without further arguments, activate
+    # the default environment. It's created when it doesn't exist yet.
+    if not env_name_or_dir and not args.temp:
+        short_name = "default"
+        if not ev.exists(short_name):
+            ev.create(short_name)
+            action = "Created and activated"
+        else:
+            action = "Activated"
+        env_path = ev.root(short_name)
+        _tty_info(f"{action} default environment in {env_path}")
+
     # Temporary environment
-    if args.temp:
+    elif args.temp:
         env = create_temp_env_directory()
         env_path = os.path.abspath(env)
         short_name = os.path.basename(env_path)
         ev.create_in_dir(env).write(regenerate=False)
+        _tty_info(f"Created and activated temporary environment in {env_path}")
 
     # Managed environment
     elif ev.exists(env_name_or_dir) and not args.dir:
@@ -380,28 +397,33 @@ def env_remove(args):
     and manifests embedded in repositories should be removed manually.
     """
     read_envs = []
+    bad_envs = []
     for env_name in args.rm_env:
-        env = ev.read(env_name)
-        read_envs.append(env)
+        try:
+            env = ev.read(env_name)
+            read_envs.append(env)
+        except (spack.config.ConfigFormatError, ev.SpackEnvironmentConfigError):
+            bad_envs.append(env_name)
 
     if not args.yes_to_all:
-        answer = tty.get_yes_or_no(
-            "Really remove %s %s?"
-            % (
-                string.plural(len(args.rm_env), "environment", show_n=False),
-                string.comma_and(args.rm_env),
-            ),
-            default=False,
-        )
+        environments = string.plural(len(args.rm_env), "environment", show_n=False)
+        envs = string.comma_and(args.rm_env)
+        answer = tty.get_yes_or_no(f"Really remove {environments} {envs}?", default=False)
         if not answer:
             tty.die("Will not remove any environments")
 
     for env in read_envs:
+        name = env.name
         if env.active:
-            tty.die("Environment %s can't be removed while activated." % env.name)
-
+            tty.die(f"Environment {name} can't be removed while activated.")
         env.destroy()
-        tty.msg("Successfully removed environment '%s'" % env.name)
+        tty.msg(f"Successfully removed environment '{name}'")
+
+    for bad_env_name in bad_envs:
+        shutil.rmtree(
+            spack.environment.environment.environment_dir_from_name(bad_env_name, exists_ok=True)
+        )
+        tty.msg(f"Successfully removed environment '{bad_env_name}'")
 
 
 #
@@ -548,8 +570,8 @@ def env_update_setup_parser(subparser):
 def env_update(args):
     manifest_file = ev.manifest_file(args.update_env)
     backup_file = manifest_file + ".bkp"
-    needs_update = not ev.is_latest_format(manifest_file)
 
+    needs_update = not ev.is_latest_format(manifest_file)
     if not needs_update:
         tty.msg('No update needed for the environment "{0}"'.format(args.update_env))
         return
@@ -667,18 +689,31 @@ def env_depfile(args):
     # Currently only make is supported.
     spack.cmd.require_active_env(cmd_name="env depfile")
 
+    env = ev.active_environment()
+
     # What things do we build when running make? By default, we build the
     # root specs. If specific specs are provided as input, we build those.
     filter_specs = spack.cmd.parse_specs(args.specs) if args.specs else None
     template = spack.tengine.make_environment().get_template(os.path.join("depfile", "Makefile"))
     model = depfile.MakefileModel.from_env(
-        ev.active_environment(),
+        env,
         filter_specs=filter_specs,
         pkg_buildcache=depfile.UseBuildCache.from_string(args.use_buildcache[0]),
         dep_buildcache=depfile.UseBuildCache.from_string(args.use_buildcache[1]),
         make_prefix=args.make_prefix,
         jobserver=args.jobserver,
     )
+
+    # Warn in case we're generating a depfile for an empty environment. We don't automatically
+    # concretize; the user should do that explicitly. Could be changed in the future if requested.
+    if model.empty:
+        if not env.user_specs:
+            tty.warn("no specs in the environment")
+        elif filter_specs is not None:
+            tty.warn("no concrete matching specs found in environment")
+        else:
+            tty.warn("environment is not concretized. Run `spack concretize` first")
+
     makefile = template.render(model.to_dict())
 
     # Finally write to stdout/file.

lib/spack/spack/cmd/gc.py

@@ -6,6 +6,7 @@
 import llnl.util.tty as tty
 
 import spack.cmd.common.arguments
+import spack.cmd.common.confirmation
 import spack.cmd.uninstall
 import spack.environment as ev
 import spack.store
@@ -41,6 +42,6 @@ def gc(parser, args):
         return
 
     if not args.yes_to_all:
-        spack.cmd.uninstall.confirm_removal(specs)
+        spack.cmd.common.confirmation.confirm_action(specs, "uninstalled", "uninstallation")
 
     spack.cmd.uninstall.do_uninstall(specs, force=False)

lib/spack/spack/cmd/info.py

@@ -3,6 +3,7 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import sys
 import textwrap
 from itertools import zip_longest
 
@@ -16,6 +17,7 @@
 import spack.install_test
 import spack.repo
 import spack.spec
+import spack.version
 from spack.package_base import preferred_version
 
 description = "get detailed information on a particular package"
@@ -53,6 +55,7 @@ def setup_parser(subparser):
         ("--tags", print_tags.__doc__),
         ("--tests", print_tests.__doc__),
         ("--virtuals", print_virtuals.__doc__),
+        ("--variants-by-name", "list variants in strict name order; don't group by condition"),
     ]
     for opt, help_comment in options:
         subparser.add_argument(opt, action="store_true", help=help_comment)
@@ -77,35 +80,10 @@ def license(s):
 
 
 class VariantFormatter:
-    def __init__(self, variants):
-        self.variants = variants
+    def __init__(self, pkg):
+        self.variants = pkg.variants
         self.headers = ("Name [Default]", "When", "Allowed values", "Description")
 
-        # Formats
-        fmt_name = "{0} [{1}]"
-
-        # Initialize column widths with the length of the
-        # corresponding headers, as they cannot be shorter
-        # than that
-        self.column_widths = [len(x) for x in self.headers]
-
-        # Expand columns based on max line lengths
-        for k, e in variants.items():
-            v, w = e
-            candidate_max_widths = (
-                len(fmt_name.format(k, self.default(v))),  # Name [Default]
-                len(str(w)),
-                len(v.allowed_values),  # Allowed values
-                len(v.description),  # Description
-            )
-
-            self.column_widths = (
-                max(self.column_widths[0], candidate_max_widths[0]),
-                max(self.column_widths[1], candidate_max_widths[1]),
-                max(self.column_widths[2], candidate_max_widths[2]),
-                max(self.column_widths[3], candidate_max_widths[3]),
-            )
-
         # Don't let name or possible values be less than max widths
         _, cols = tty.terminal_size()
         max_name = min(self.column_widths[0], 30)
@@ -137,6 +115,8 @@ def default(self, v):
     def lines(self):
         if not self.variants:
             yield "    None"
+            return
+
         else:
             yield "    " + self.fmt % self.headers
             underline = tuple([w * "=" for w in self.column_widths])
@@ -271,15 +251,165 @@ def print_tests(pkg):
         color.cprint("    None")
 
 
-def print_variants(pkg):
+def _fmt_value(v):
+    if v is None or isinstance(v, bool):
+        return str(v).lower()
+    else:
+        return str(v)
+
+
+def _fmt_name_and_default(variant):
+    """Print colorized name [default] for a variant."""
+    return color.colorize(f"@c{{{variant.name}}} @C{{[{_fmt_value(variant.default)}]}}")
+
+
+def _fmt_when(when, indent):
+    return color.colorize(f"{indent * ' '}@B{{when}} {color.cescape(when)}")
+
+
+def _fmt_variant_description(variant, width, indent):
+    """Format a variant's description, preserving explicit line breaks."""
+    return "\n".join(
+        textwrap.fill(
+            line, width=width, initial_indent=indent * " ", subsequent_indent=indent * " "
+        )
+        for line in variant.description.split("\n")
+    )
+
+
+def _fmt_variant(variant, max_name_default_len, indent, when=None, out=None):
+    out = out or sys.stdout
+
+    _, cols = tty.terminal_size()
+
+    name_and_default = _fmt_name_and_default(variant)
+    name_default_len = color.clen(name_and_default)
+
+    values = variant.values
+    if not isinstance(variant.values, (tuple, list, spack.variant.DisjointSetsOfValues)):
+        values = [variant.values]
+
+    # put 'none' first, sort the rest by value
+    sorted_values = sorted(values, key=lambda v: (v != "none", v))
+
+    pad = 4  # min padding between 'name [default]' and values
+    value_indent = (indent + max_name_default_len + pad) * " "  # left edge of values
+
+    # This preserves any formatting (i.e., newlines) from how the description was
+    # written in package.py, but still wraps long lines for small terminals.
+    # This allows some packages to provide detailed help on their variants (see, e.g., gasnet).
+    formatted_values = "\n".join(
+        textwrap.wrap(
+            f"{', '.join(_fmt_value(v) for v in sorted_values)}",
+            width=cols - 2,
+            initial_indent=value_indent,
+            subsequent_indent=value_indent,
+        )
+    )
+    formatted_values = formatted_values[indent + name_default_len + pad :]
+
+    # name [default]   value1, value2, value3, ...
+    padding = pad * " "
+    color.cprint(f"{indent * ' '}{name_and_default}{padding}@c{{{formatted_values}}}", stream=out)
+
+    # when <spec>
+    description_indent = indent + 4
+    if when is not None and when != spack.spec.Spec():
+        out.write(_fmt_when(when, description_indent - 2))
+        out.write("\n")
+
+    # description, preserving explicit line breaks from the way it's written in the package file
+    out.write(_fmt_variant_description(variant, cols - 2, description_indent))
+    out.write("\n")
+
+
+def _variants_by_name_when(pkg):
+    """Adaptor to get variants keyed by { name: { when: { [Variant...] } }."""
+    # TODO: replace with pkg.variants_by_name(when=True) when unified directive dicts are merged.
+    variants = {}
+    for name, (variant, whens) in pkg.variants.items():
+        for when in whens:
+            variants.setdefault(name, {}).setdefault(when, []).append(variant)
+    return variants
+
+
+def _variants_by_when_name(pkg):
+    """Adaptor to get variants keyed by { when: { name: Variant } }"""
+    # TODO: replace with pkg.variants when unified directive dicts are merged.
+    variants = {}
+    for name, (variant, whens) in pkg.variants.items():
+        for when in whens:
+            variants.setdefault(when, {})[name] = variant
+    return variants
+
+
+def _print_variants_header(pkg):
     """output variants"""
 
+    if not pkg.variants:
+        print("    None")
+        return
+
     color.cprint("")
     color.cprint(section_title("Variants:"))
 
-    formatter = VariantFormatter(pkg.variants)
-    for line in formatter.lines:
-        color.cprint(color.cescape(line))
+    variants_by_name = _variants_by_name_when(pkg)
+
+    # Calculate the max length of the "name [default]" part of the variant display
+    # This lets us know where to print variant values.
+    max_name_default_len = max(
+        color.clen(_fmt_name_and_default(variant))
+        for name, when_variants in variants_by_name.items()
+        for variants in when_variants.values()
+        for variant in variants
+    )
+
+    return max_name_default_len, variants_by_name
+
+
+def _unconstrained_ver_first(item):
+    """sort key that puts specs with open version ranges first"""
+    spec, _ = item
+    return (spack.version.any_version not in spec.versions, spec)
+
+
+def print_variants_grouped_by_when(pkg):
+    max_name_default_len, _ = _print_variants_header(pkg)
+
+    indent = 4
+    variants = _variants_by_when_name(pkg)
+    for when, variants_by_name in sorted(variants.items(), key=_unconstrained_ver_first):
+        padded_values = max_name_default_len + 4
+        start_indent = indent
+
+        if when != spack.spec.Spec():
+            sys.stdout.write("\n")
+            sys.stdout.write(_fmt_when(when, indent))
+            sys.stdout.write("\n")
+
+            # indent names slightly inside 'when', but line up values
+            padded_values -= 2
+            start_indent += 2
+
+        for name, variant in sorted(variants_by_name.items()):
+            _fmt_variant(variant, padded_values, start_indent, None, out=sys.stdout)
+
+
+def print_variants_by_name(pkg):
+    max_name_default_len, variants_by_name = _print_variants_header(pkg)
+    max_name_default_len += 4
+
+    indent = 4
+    for name, when_variants in variants_by_name.items():
+        for when, variants in sorted(when_variants.items(), key=_unconstrained_ver_first):
+            for variant in variants:
+                _fmt_variant(variant, max_name_default_len, indent, when, out=sys.stdout)
+                sys.stdout.write("\n")
+
+
+def print_variants(pkg):
+    """output variants"""
+    print_variants_grouped_by_when(pkg)
 
 
 def print_versions(pkg):
@@ -300,18 +430,24 @@ def print_versions(pkg):
         pad = padder(pkg.versions, 4)
 
         preferred = preferred_version(pkg)
-        url = ""
-        if pkg.has_code:
-            url = fs.for_package_version(pkg, preferred)
 
+        def get_url(version):
+            try:
+                return fs.for_package_version(pkg, version)
+            except spack.fetch_strategy.InvalidArgsError:
+                return "No URL"
+
+        url = get_url(preferred) if pkg.has_code else ""
         line = version("    {0}".format(pad(preferred))) + color.cescape(url)
-        color.cprint(line)
+        color.cwrite(line)
+
+        print()
 
         safe = []
         deprecated = []
         for v in reversed(sorted(pkg.versions)):
             if pkg.has_code:
-                url = fs.for_package_version(pkg, v)
+                url = get_url(v)
             if pkg.versions[v].get("deprecated", False):
                 deprecated.append((v, url))
             else:
@@ -384,7 +520,12 @@ def info(parser, args):
     else:
         color.cprint("    None")
 
-    color.cprint(section_title("Homepage: ") + pkg.homepage)
+    if getattr(pkg, "homepage"):
+        color.cprint(section_title("Homepage: ") + pkg.homepage)
+
+    _print_variants = (
+        print_variants_by_name if args.variants_by_name else print_variants_grouped_by_when
+    )
 
     # Now output optional information in expected order
     sections = [
@@ -392,7 +533,7 @@ def info(parser, args):
         (args.all or args.detectable, print_detectable),
         (args.all or args.tags, print_tags),
         (args.all or not args.no_versions, print_versions),
-        (args.all or not args.no_variants, print_variants),
+        (args.all or not args.no_variants, _print_variants),
         (args.all or args.phases, print_phases),
         (args.all or not args.no_dependencies, print_dependencies),
         (args.all or args.virtuals, print_virtuals),

lib/spack/spack/cmd/mirror.py

@@ -111,7 +111,7 @@ def setup_parser(subparser):
             "and source use `--type binary --type source` (default)"
         ),
     )
-    arguments.add_s3_connection_args(add_parser, False)
+    arguments.add_connection_args(add_parser, False)
     # Remove
     remove_parser = sp.add_parser("remove", aliases=["rm"], help=mirror_remove.__doc__)
     remove_parser.add_argument("name", help="mnemonic name for mirror", metavar="mirror")
@@ -141,7 +141,7 @@ def setup_parser(subparser):
         default=spack.config.default_modify_scope(),
         help="configuration scope to modify",
     )
-    arguments.add_s3_connection_args(set_url_parser, False)
+    arguments.add_connection_args(set_url_parser, False)
 
     # Set
     set_parser = sp.add_parser("set", help=mirror_set.__doc__)
@@ -170,7 +170,7 @@ def setup_parser(subparser):
         default=spack.config.default_modify_scope(),
         help="configuration scope to modify",
     )
-    arguments.add_s3_connection_args(set_parser, False)
+    arguments.add_connection_args(set_parser, False)
 
     # List
     list_parser = sp.add_parser("list", help=mirror_list.__doc__)
@@ -192,6 +192,8 @@ def mirror_add(args):
         or args.s3_profile
         or args.s3_endpoint_url
         or args.type
+        or args.oci_username
+        or args.oci_password
     ):
         connection = {"url": args.url}
         if args.s3_access_key_id and args.s3_access_key_secret:
@@ -202,6 +204,8 @@ def mirror_add(args):
             connection["profile"] = args.s3_profile
         if args.s3_endpoint_url:
             connection["endpoint_url"] = args.s3_endpoint_url
+        if args.oci_username and args.oci_password:
+            connection["access_pair"] = [args.oci_username, args.oci_password]
         if args.type:
             connection["binary"] = "binary" in args.type
             connection["source"] = "source" in args.type
@@ -235,6 +239,8 @@ def _configure_mirror(args):
         changes["profile"] = args.s3_profile
     if args.s3_endpoint_url:
         changes["endpoint_url"] = args.s3_endpoint_url
+    if args.oci_username and args.oci_password:
+        changes["access_pair"] = [args.oci_username, args.oci_password]
 
     # argparse cannot distinguish between --binary and --no-binary when same dest :(
     # notice that set-url does not have these args, so getattr

lib/spack/spack/cmd/tutorial.py

@@ -23,7 +23,7 @@
 
 
 # tutorial configuration parameters
-tutorial_branch = "releases/v0.20"
+tutorial_branch = "releases/v0.21"
 tutorial_mirror = "file:///mirror"
 tutorial_key = os.path.join(spack.paths.share_path, "keys", "tutorial.pub")
 

lib/spack/spack/cmd/uninstall.py

@@ -11,10 +11,9 @@
 
 import spack.cmd
 import spack.cmd.common.arguments as arguments
+import spack.cmd.common.confirmation as confirmation
 import spack.environment as ev
-import spack.error
 import spack.package_base
-import spack.repo
 import spack.spec
 import spack.store
 import spack.traverse as traverse
@@ -278,7 +277,7 @@ def uninstall_specs(args, specs):
         return
 
     if not args.yes_to_all:
-        confirm_removal(uninstall_list)
+        confirmation.confirm_action(uninstall_list, "uninstalled", "uninstallation")
 
     # Uninstall everything on the list
     do_uninstall(uninstall_list, args.force)
@@ -292,21 +291,6 @@ def uninstall_specs(args, specs):
         env.regenerate_views()
 
 
-def confirm_removal(specs: List[spack.spec.Spec]):
-    """Display the list of specs to be removed and ask for confirmation.
-
-    Args:
-        specs: specs to be removed
-    """
-    tty.msg("The following {} packages will be uninstalled:\n".format(len(specs)))
-    spack.cmd.display_specs(specs, **display_args)
-    print("")
-    answer = tty.get_yes_or_no("Do you want to proceed?", default=False)
-    if not answer:
-        tty.msg("Aborting uninstallation")
-        sys.exit(0)
-
-
 def uninstall(parser, args):
     if not args.specs and not args.all:
         tty.die(

lib/spack/spack/compilers/__init__.py

@@ -10,7 +10,7 @@
 import itertools
 import multiprocessing.pool
 import os
-from typing import Dict, List
+from typing import Dict, List, Optional, Tuple
 
 import archspec.cpu
 
@@ -21,6 +21,7 @@
 import spack.compiler
 import spack.config
 import spack.error
+import spack.operating_systems
 import spack.paths
 import spack.platforms
 import spack.spec
@@ -223,13 +224,16 @@ def all_compiler_specs(scope=None, init_config=True):
     ]
 
 
-def find_compilers(path_hints=None):
+def find_compilers(
+    path_hints: Optional[List[str]] = None, *, mixed_toolchain=False
+) -> List["spack.compiler.Compiler"]:
     """Return the list of compilers found in the paths given as arguments.
 
     Args:
-        path_hints (list or None): list of path hints where to look for.
-            A sensible default based on the ``PATH`` environment variable
-            will be used if the value is None
+        path_hints: list of path hints where to look for. A sensible default based on the ``PATH``
+            environment variable will be used if the value is None
+        mixed_toolchain: allow mixing compilers from different toolchains if otherwise missing for
+            a certain language
     """
     if path_hints is None:
         path_hints = get_path("PATH")
@@ -250,7 +254,7 @@ def find_compilers(path_hints=None):
     finally:
         tp.close()
 
-    def valid_version(item):
+    def valid_version(item: Tuple[Optional[DetectVersionArgs], Optional[str]]) -> bool:
         value, error = item
         if error is None:
             return True
@@ -262,25 +266,37 @@ def valid_version(item):
             pass
         return False
 
-    def remove_errors(item):
+    def remove_errors(
+        item: Tuple[Optional[DetectVersionArgs], Optional[str]]
+    ) -> DetectVersionArgs:
         value, _ = item
+        assert value is not None
         return value
 
-    return make_compiler_list(map(remove_errors, filter(valid_version, detected_versions)))
+    return make_compiler_list(
+        [remove_errors(detected) for detected in detected_versions if valid_version(detected)],
+        mixed_toolchain=mixed_toolchain,
+    )
 
 
-def find_new_compilers(path_hints=None, scope=None):
+def find_new_compilers(
+    path_hints: Optional[List[str]] = None,
+    scope: Optional[str] = None,
+    *,
+    mixed_toolchain: bool = False,
+):
     """Same as ``find_compilers`` but return only the compilers that are not
     already in compilers.yaml.
 
     Args:
-        path_hints (list or None): list of path hints where to look for.
-            A sensible default based on the ``PATH`` environment variable
-            will be used if the value is None
-        scope (str): scope to look for a compiler. If None consider the
-            merged configuration.
+        path_hints: list of path hints where to look for. A sensible default based on the ``PATH``
+            environment variable will be used if the value is None
+        scope: scope to look for a compiler. If None consider the merged configuration.
+        mixed_toolchain: allow mixing compilers from different toolchains if otherwise missing for
+            a certain language
     """
-    compilers = find_compilers(path_hints)
+    compilers = find_compilers(path_hints, mixed_toolchain=mixed_toolchain)
+
     return select_new_compilers(compilers, scope)
 
 
@@ -638,7 +654,9 @@ def all_compiler_types():
 )
 
 
-def arguments_to_detect_version_fn(operating_system, paths):
+def arguments_to_detect_version_fn(
+    operating_system: spack.operating_systems.OperatingSystem, paths: List[str]
+) -> List[DetectVersionArgs]:
     """Returns a list of DetectVersionArgs tuples to be used in a
     corresponding function to detect compiler versions.
 
@@ -646,8 +664,7 @@ def arguments_to_detect_version_fn(operating_system, paths):
     function by providing a method called with the same name.
 
     Args:
-        operating_system (spack.operating_systems.OperatingSystem): the operating system
-            on which we are looking for compilers
+        operating_system: the operating system on which we are looking for compilers
         paths: paths to search for compilers
 
     Returns:
@@ -656,10 +673,10 @@ def arguments_to_detect_version_fn(operating_system, paths):
         compilers in this OS.
     """
 
-    def _default(search_paths):
-        command_arguments = []
+    def _default(search_paths: List[str]) -> List[DetectVersionArgs]:
+        command_arguments: List[DetectVersionArgs] = []
         files_to_be_tested = fs.files_in(*search_paths)
-        for compiler_name in spack.compilers.supported_compilers_for_host_platform():
+        for compiler_name in supported_compilers_for_host_platform():
             compiler_cls = class_for_compiler_name(compiler_name)
 
             for language in ("cc", "cxx", "f77", "fc"):
@@ -684,7 +701,9 @@ def _default(search_paths):
     return fn(paths)
 
 
-def detect_version(detect_version_args):
+def detect_version(
+    detect_version_args: DetectVersionArgs,
+) -> Tuple[Optional[DetectVersionArgs], Optional[str]]:
     """Computes the version of a compiler and adds it to the information
     passed as input.
 
@@ -693,8 +712,7 @@ def detect_version(detect_version_args):
     needs to be checked by the code dispatching the calls.
 
     Args:
-        detect_version_args (DetectVersionArgs): information on the
-            compiler for which we should detect the version.
+        detect_version_args: information on the compiler for which we should detect the version.
 
     Returns:
         A ``(DetectVersionArgs, error)`` tuple. If ``error`` is ``None`` the
@@ -710,7 +728,7 @@ def _default(fn_args):
         path = fn_args.path
 
         # Get compiler names and the callback to detect their versions
-        callback = getattr(compiler_cls, "{0}_version".format(language))
+        callback = getattr(compiler_cls, f"{language}_version")
 
         try:
             version = callback(path)
@@ -736,13 +754,15 @@ def _default(fn_args):
     return fn(detect_version_args)
 
 
-def make_compiler_list(detected_versions):
+def make_compiler_list(
+    detected_versions: List[DetectVersionArgs], mixed_toolchain: bool = False
+) -> List["spack.compiler.Compiler"]:
     """Process a list of detected versions and turn them into a list of
     compiler specs.
 
     Args:
-        detected_versions (list): list of DetectVersionArgs containing a
-            valid version
+        detected_versions: list of DetectVersionArgs containing a valid version
+        mixed_toolchain: allow mixing compilers from different toolchains if langauge is missing
 
     Returns:
         list: list of Compiler objects
@@ -751,7 +771,7 @@ def make_compiler_list(detected_versions):
     sorted_compilers = sorted(detected_versions, key=group_fn)
 
     # Gather items in a dictionary by the id, name variation and language
-    compilers_d = {}
+    compilers_d: Dict[CompilerID, Dict[NameVariation, dict]] = {}
     for sort_key, group in itertools.groupby(sorted_compilers, key=group_fn):
         compiler_id, name_variation, language = sort_key
         by_compiler_id = compilers_d.setdefault(compiler_id, {})
@@ -760,7 +780,7 @@ def make_compiler_list(detected_versions):
 
     def _default_make_compilers(cmp_id, paths):
         operating_system, compiler_name, version = cmp_id
-        compiler_cls = spack.compilers.class_for_compiler_name(compiler_name)
+        compiler_cls = class_for_compiler_name(compiler_name)
         spec = spack.spec.CompilerSpec(compiler_cls.name, f"={version}")
         paths = [paths.get(x, None) for x in ("cc", "cxx", "f77", "fc")]
         # TODO: johnwparent - revist the following line as per discussion at:
@@ -782,13 +802,14 @@ def _default_make_compilers(cmp_id, paths):
         getattr(variation, "suffix", None),
     )
 
-    compilers = []
+    # Flatten to a list of compiler id, primary variation and compiler dictionary
+    flat_compilers: List[Tuple[CompilerID, NameVariation, dict]] = []
     for compiler_id, by_compiler_id in compilers_d.items():
         ordered = sorted(by_compiler_id, key=sort_fn)
         selected_variation = ordered[0]
         selected = by_compiler_id[selected_variation]
 
-        # fill any missing parts from subsequent entries
+        # Fill any missing parts from subsequent entries (without mixing toolchains)
         for lang in ["cxx", "f77", "fc"]:
             if lang not in selected:
                 next_lang = next(
@@ -797,14 +818,63 @@ def _default_make_compilers(cmp_id, paths):
                 if next_lang:
                     selected[lang] = next_lang
 
-        operating_system, _, _ = compiler_id
-        make_compilers = getattr(operating_system, "make_compilers", _default_make_compilers)
+        flat_compilers.append((compiler_id, selected_variation, selected))
 
-        compilers.extend(make_compilers(compiler_id, selected))
+    # Next, fill out the blanks of missing compilers by creating a mixed toolchain (if requested)
+    if mixed_toolchain:
+        make_mixed_toolchain(flat_compilers)
+
+    # Finally, create the compiler list
+    compilers = []
+    for compiler_id, _, compiler in flat_compilers:
+        make_compilers = getattr(compiler_id.os, "make_compilers", _default_make_compilers)
+        compilers.extend(make_compilers(compiler_id, compiler))
 
     return compilers
 
 
+def make_mixed_toolchain(compilers: List[Tuple[CompilerID, NameVariation, dict]]) -> None:
+    """Add missing compilers across toolchains when they are missing for a particular language.
+    This currently only adds the most sensible gfortran to (apple)-clang if it doesn't have a
+    fortran compiler (no flang)."""
+
+    # First collect the clangs that are missing a fortran compiler
+    clangs_without_flang = [
+        (id, variation, compiler)
+        for id, variation, compiler in compilers
+        if id.compiler_name in ("clang", "apple-clang")
+        and "f77" not in compiler
+        and "fc" not in compiler
+    ]
+    if not clangs_without_flang:
+        return
+
+    # Filter on GCCs with fortran compiler
+    gccs_with_fortran = [
+        (id, variation, compiler)
+        for id, variation, compiler in compilers
+        if id.compiler_name == "gcc" and "f77" in compiler and "fc" in compiler
+    ]
+
+    # Sort these GCCs by "best variation" (no prefix / suffix first)
+    gccs_with_fortran.sort(
+        key=lambda x: (getattr(x[1], "prefix", None), getattr(x[1], "suffix", None))
+    )
+
+    # Attach the optimal GCC fortran compiler to the clangs that don't have one
+    for clang_id, _, clang_compiler in clangs_without_flang:
+        gcc_compiler = next(
+            (gcc[2] for gcc in gccs_with_fortran if gcc[0].os == clang_id.os), None
+        )
+
+        if not gcc_compiler:
+            continue
+
+        # Update the fc / f77 entries
+        clang_compiler["f77"] = gcc_compiler["f77"]
+        clang_compiler["fc"] = gcc_compiler["fc"]
+
+
 def is_mixed_toolchain(compiler):
     """Returns True if the current compiler is a mixed toolchain,
     False otherwise.

lib/spack/spack/compilers/aocc.py

@@ -5,7 +5,6 @@
 
 import os
 import re
-import sys
 
 import llnl.util.lang
 
@@ -114,17 +113,6 @@ def extract_version_from_output(cls, output):
             return ".".join(match.groups())
         return "unknown"
 
-    @classmethod
-    def fc_version(cls, fortran_compiler):
-        if sys.platform == "darwin":
-            return cls.default_version("clang")
-
-        return cls.default_version(fortran_compiler)
-
-    @classmethod
-    def f77_version(cls, f77):
-        return cls.fc_version(f77)
-
     @property
     def stdcxx_libs(self):
         return ("-lstdc++",)

lib/spack/spack/compilers/clang.py

@@ -5,7 +5,6 @@
 
 import os
 import re
-import sys
 
 import llnl.util.lang
 
@@ -39,10 +38,10 @@ class Clang(Compiler):
     cxx_names = ["clang++"]
 
     # Subclasses use possible names of Fortran 77 compiler
-    f77_names = ["flang", "gfortran", "xlf_r"]
+    f77_names = ["flang"]
 
     # Subclasses use possible names of Fortran 90 compiler
-    fc_names = ["flang", "gfortran", "xlf90_r"]
+    fc_names = ["flang"]
 
     version_argument = "--version"
 
@@ -182,16 +181,3 @@ def extract_version_from_output(cls, output):
         if match:
             ver = match.group(match.lastindex)
         return ver
-
-    @classmethod
-    def fc_version(cls, fc):
-        # We could map from gcc/gfortran version to clang version, but on macOS
-        # we normally mix any version of gfortran with any version of clang.
-        if sys.platform == "darwin":
-            return cls.default_version("clang")
-        else:
-            return cls.default_version(fc)
-
-    @classmethod
-    def f77_version(cls, f77):
-        return cls.fc_version(f77)

lib/spack/spack/config.py

@@ -69,6 +69,7 @@
 SECTION_SCHEMAS = {
     "compilers": spack.schema.compilers.schema,
     "concretizer": spack.schema.concretizer.schema,
+    "definitions": spack.schema.definitions.schema,
     "mirrors": spack.schema.mirrors.schema,
     "repos": spack.schema.repos.schema,
     "packages": spack.schema.packages.schema,
@@ -994,6 +995,7 @@ def read_config_file(filename, schema=None):
                 key = next(iter(data))
                 schema = _ALL_SCHEMAS[key]
             validate(data, schema)
+
         return data
 
     except StopIteration:

lib/spack/spack/database.py

@@ -1522,14 +1522,18 @@ def _query(
         # TODO: like installed and known that can be queried?  Or are
         # TODO: these really special cases that only belong here?
 
-        # Just look up concrete specs with hashes; no fancy search.
-        if isinstance(query_spec, spack.spec.Spec) and query_spec.concrete:
-            # TODO: handling of hashes restriction is not particularly elegant.
-            hash_key = query_spec.dag_hash()
-            if hash_key in self._data and (not hashes or hash_key in hashes):
-                return [self._data[hash_key].spec]
-            else:
-                return []
+        if query_spec is not any:
+            if not isinstance(query_spec, spack.spec.Spec):
+                query_spec = spack.spec.Spec(query_spec)
+
+            # Just look up concrete specs with hashes; no fancy search.
+            if query_spec.concrete:
+                # TODO: handling of hashes restriction is not particularly elegant.
+                hash_key = query_spec.dag_hash()
+                if hash_key in self._data and (not hashes or hash_key in hashes):
+                    return [self._data[hash_key].spec]
+                else:
+                    return []
 
         # Abstract specs require more work -- currently we test
         # against everything.
@@ -1537,6 +1541,9 @@ def _query(
         start_date = start_date or datetime.datetime.min
         end_date = end_date or datetime.datetime.max
 
+        # save specs whose name doesn't match for last, to avoid a virtual check
+        deferred = []
+
         for key, rec in self._data.items():
             if hashes is not None and rec.spec.dag_hash() not in hashes:
                 continue
@@ -1561,8 +1568,26 @@ def _query(
                 if not (start_date < inst_date < end_date):
                     continue
 
-            if query_spec is any or rec.spec.satisfies(query_spec):
+            if query_spec is any:
                 results.append(rec.spec)
+                continue
+
+            # check anon specs and exact name matches first
+            if not query_spec.name or rec.spec.name == query_spec.name:
+                if rec.spec.satisfies(query_spec):
+                    results.append(rec.spec)
+
+            # save potential virtual matches for later, but not if we already found a match
+            elif not results:
+                deferred.append(rec.spec)
+
+        # Checking for virtuals is expensive, so we save it for last and only if needed.
+        # If we get here, we didn't find anything in the DB that matched by name.
+        # If we did fine something, the query spec can't be virtual b/c we matched an actual
+        # package installation, so skip the virtual check entirely. If we *didn't* find anything,
+        # check all the deferred specs *if* the query is virtual.
+        if not results and query_spec is not any and deferred and query_spec.virtual:
+            results = [spec for spec in deferred if spec.satisfies(query_spec)]
 
         return results
 

lib/spack/spack/detection/common.py

@@ -269,7 +269,7 @@ def find_windows_compiler_root_paths() -> List[str]:
 
         At the moment simply returns location of VS install paths from VSWhere
         But should be extended to include more information as relevant"""
-        return list(winOs.WindowsOs.vs_install_paths)
+        return list(winOs.WindowsOs().vs_install_paths)
 
     @staticmethod
     def find_windows_compiler_cmake_paths() -> List[str]:

lib/spack/spack/detection/path.py

@@ -15,9 +15,12 @@
 from typing import Dict, List, Optional, Set, Tuple
 
 import llnl.util.filesystem
+import llnl.util.lang
 import llnl.util.tty
 
+import spack.util.elf as elf_utils
 import spack.util.environment
+import spack.util.environment as environment
 import spack.util.ld_so_conf
 
 from .common import (
@@ -39,15 +42,29 @@
     DETECTION_TIMEOUT = 120
 
 
-def common_windows_package_paths() -> List[str]:
+def common_windows_package_paths(pkg_cls=None) -> List[str]:
+    """Get the paths for common package installation location on Windows
+    that are outside the PATH
+    Returns [] on unix
+    """
+    if sys.platform != "win32":
+        return []
     paths = WindowsCompilerExternalPaths.find_windows_compiler_bundled_packages()
     paths.extend(find_win32_additional_install_paths())
     paths.extend(WindowsKitExternalPaths.find_windows_kit_bin_paths())
     paths.extend(WindowsKitExternalPaths.find_windows_kit_reg_installed_roots_paths())
     paths.extend(WindowsKitExternalPaths.find_windows_kit_reg_sdk_paths())
+    if pkg_cls:
+        paths.extend(compute_windows_user_path_for_package(pkg_cls))
+        paths.extend(compute_windows_program_path_for_package(pkg_cls))
     return paths
 
 
+def file_identifier(path):
+    s = os.stat(path)
+    return (s.st_dev, s.st_ino)
+
+
 def executables_in_path(path_hints: List[str]) -> Dict[str, str]:
     """Get the paths of all executables available from the current PATH.
 
@@ -62,18 +79,44 @@ def executables_in_path(path_hints: List[str]) -> Dict[str, str]:
         path_hints: list of paths to be searched. If None the list will be
             constructed based on the PATH environment variable.
     """
-    if sys.platform == "win32":
-        path_hints.extend(common_windows_package_paths())
     search_paths = llnl.util.filesystem.search_paths_for_executables(*path_hints)
     return path_to_dict(search_paths)
 
 
+def get_elf_compat(path):
+    """For ELF files, get a triplet (EI_CLASS, EI_DATA, e_machine) and see if
+    it is host-compatible."""
+    # On ELF platforms supporting, we try to be a bit smarter when it comes to shared
+    # libraries, by dropping those that are not host compatible.
+    with open(path, "rb") as f:
+        elf = elf_utils.parse_elf(f, only_header=True)
+        return (elf.is_64_bit, elf.is_little_endian, elf.elf_hdr.e_machine)
+
+
+def accept_elf(path, host_compat):
+    """Accept an ELF file if the header matches the given compat triplet,
+    obtained with :py:func:`get_elf_compat`. In case it's not an ELF (e.g.
+    static library, or some arbitrary file, fall back to is_readable_file)."""
+    # Fast path: assume libraries at least have .so in their basename.
+    # Note: don't replace with splitext, because of libsmth.so.1.2.3 file names.
+    if ".so" not in os.path.basename(path):
+        return llnl.util.filesystem.is_readable_file(path)
+    try:
+        return host_compat == get_elf_compat(path)
+    except (OSError, elf_utils.ElfParsingError):
+        return llnl.util.filesystem.is_readable_file(path)
+
+
 def libraries_in_ld_and_system_library_path(
     path_hints: Optional[List[str]] = None,
 ) -> Dict[str, str]:
-    """Get the paths of all libraries available from LD_LIBRARY_PATH,
-    LIBRARY_PATH, DYLD_LIBRARY_PATH, DYLD_FALLBACK_LIBRARY_PATH, and
-    standard system library paths.
+    """Get the paths of all libraries available from ``path_hints`` or the
+    following defaults:
+
+    - Environment variables (Linux: ``LD_LIBRARY_PATH``, Darwin: ``DYLD_LIBRARY_PATH``,
+      and ``DYLD_FALLBACK_LIBRARY_PATH``)
+    - Dynamic linker default paths (glibc: ld.so.conf, musl: ld-musl-<arch>.path)
+    - Default system library paths.
 
     For convenience, this is constructed as a dictionary where the keys are
     the library paths and the values are the names of the libraries
@@ -87,31 +130,71 @@ def libraries_in_ld_and_system_library_path(
             constructed based on the set of LD_LIBRARY_PATH, LIBRARY_PATH,
             DYLD_LIBRARY_PATH, and DYLD_FALLBACK_LIBRARY_PATH environment
             variables as well as the standard system library paths.
+        path_hints (list): list of paths to be searched. If ``None``, the default
+            system paths are used.
     """
-    path_hints = (
-        path_hints
-        or spack.util.environment.get_path("LD_LIBRARY_PATH")
-        + spack.util.environment.get_path("DYLD_LIBRARY_PATH")
-        + spack.util.environment.get_path("DYLD_FALLBACK_LIBRARY_PATH")
-        + spack.util.ld_so_conf.host_dynamic_linker_search_paths()
+    if path_hints:
+        search_paths = llnl.util.filesystem.search_paths_for_libraries(*path_hints)
+    else:
+        search_paths = []
+
+        # Environment variables
+        if sys.platform == "darwin":
+            search_paths.extend(environment.get_path("DYLD_LIBRARY_PATH"))
+            search_paths.extend(environment.get_path("DYLD_FALLBACK_LIBRARY_PATH"))
+        elif sys.platform.startswith("linux"):
+            search_paths.extend(environment.get_path("LD_LIBRARY_PATH"))
+
+        # Dynamic linker paths
+        search_paths.extend(spack.util.ld_so_conf.host_dynamic_linker_search_paths())
+
+        # Drop redundant paths
+        search_paths = list(filter(os.path.isdir, search_paths))
+
+    # Make use we don't doubly list /usr/lib and /lib etc
+    search_paths = list(llnl.util.lang.dedupe(search_paths, key=file_identifier))
+
+    try:
+        host_compat = get_elf_compat(sys.executable)
+        accept = lambda path: accept_elf(path, host_compat)
+    except (OSError, elf_utils.ElfParsingError):
+        accept = llnl.util.filesystem.is_readable_file
+
+    path_to_lib = {}
+    # Reverse order of search directories so that a lib in the first
+    # search path entry overrides later entries
+    for search_path in reversed(search_paths):
+        for lib in os.listdir(search_path):
+            lib_path = os.path.join(search_path, lib)
+            if accept(lib_path):
+                path_to_lib[lib_path] = lib
+    return path_to_lib
+
+
+def libraries_in_windows_paths(path_hints: Optional[List[str]] = None) -> Dict[str, str]:
+    """Get the paths of all libraries available from the system PATH paths.
+
+    For more details, see `libraries_in_ld_and_system_library_path` regarding
+    return type and contents.
+
+    Args:
+        path_hints: list of paths to be searched. If None the list will be
+            constructed based on the set of PATH environment
+            variables as well as the standard system library paths.
+    """
+    search_hints = (
+        path_hints if path_hints is not None else spack.util.environment.get_path("PATH")
     )
-    search_paths = llnl.util.filesystem.search_paths_for_libraries(*path_hints)
-    return path_to_dict(search_paths)
-
-
-def libraries_in_windows_paths(path_hints: List[str]) -> Dict[str, str]:
-    path_hints.extend(spack.util.environment.get_path("PATH"))
-    search_paths = llnl.util.filesystem.search_paths_for_libraries(*path_hints)
+    search_paths = llnl.util.filesystem.search_paths_for_libraries(*search_hints)
     # on Windows, some libraries (.dlls) are found in the bin directory or sometimes
     # at the search root. Add both of those options to the search scheme
-    search_paths.extend(llnl.util.filesystem.search_paths_for_executables(*path_hints))
-    search_paths.extend(WindowsKitExternalPaths.find_windows_kit_lib_paths())
-    search_paths.extend(WindowsKitExternalPaths.find_windows_kit_bin_paths())
-    search_paths.extend(WindowsKitExternalPaths.find_windows_kit_reg_installed_roots_paths())
-    search_paths.extend(WindowsKitExternalPaths.find_windows_kit_reg_sdk_paths())
-    # SDK and WGL should be handled by above, however on occasion the WDK is in an atypical
-    # location, so we handle that case specifically.
-    search_paths.extend(WindowsKitExternalPaths.find_windows_driver_development_kit_paths())
+    search_paths.extend(llnl.util.filesystem.search_paths_for_executables(*search_hints))
+    if path_hints is None:
+        # if no user provided path was given, add defaults to the search
+        search_paths.extend(WindowsKitExternalPaths.find_windows_kit_lib_paths())
+        # SDK and WGL should be handled by above, however on occasion the WDK is in an atypical
+        # location, so we handle that case specifically.
+        search_paths.extend(WindowsKitExternalPaths.find_windows_driver_development_kit_paths())
     return path_to_dict(search_paths)
 
 
@@ -125,19 +208,8 @@ def _group_by_prefix(paths: Set[str]) -> Dict[str, Set[str]]:
 class Finder:
     """Inspects the file-system looking for packages. Guesses places where to look using PATH."""
 
-    def path_hints(
-        self, *, pkg: "spack.package_base.PackageBase", initial_guess: Optional[List[str]] = None
-    ) -> List[str]:
-        """Returns the list of paths to be searched.
-
-        Args:
-            pkg: package being detected
-            initial_guess: initial list of paths from caller
-        """
-        result = initial_guess or []
-        result.extend(compute_windows_user_path_for_package(pkg))
-        result.extend(compute_windows_program_path_for_package(pkg))
-        return result
+    def default_path_hints(self) -> List[str]:
+        return []
 
     def search_patterns(self, *, pkg: "spack.package_base.PackageBase") -> List[str]:
         """Returns the list of patterns used to match candidate files.
@@ -245,6 +317,8 @@ def find(
         Args:
             pkg_name: package being detected
             initial_guess: initial list of paths to search from the caller
+                           if None, default paths are searched. If this
+                           is an empty list, nothing will be searched.
         """
         import spack.repo
 
@@ -252,13 +326,18 @@ def find(
         patterns = self.search_patterns(pkg=pkg_cls)
         if not patterns:
             return []
-        path_hints = self.path_hints(pkg=pkg_cls, initial_guess=initial_guess)
-        candidates = self.candidate_files(patterns=patterns, paths=path_hints)
+        if initial_guess is None:
+            initial_guess = self.default_path_hints()
+            initial_guess.extend(common_windows_package_paths(pkg_cls))
+        candidates = self.candidate_files(patterns=patterns, paths=initial_guess)
         result = self.detect_specs(pkg=pkg_cls, paths=candidates)
         return result
 
 
 class ExecutablesFinder(Finder):
+    def default_path_hints(self) -> List[str]:
+        return spack.util.environment.get_path("PATH")
+
     def search_patterns(self, *, pkg: "spack.package_base.PackageBase") -> List[str]:
         result = []
         if hasattr(pkg, "executables") and hasattr(pkg, "platform_executables"):
@@ -298,7 +377,7 @@ def candidate_files(self, *, patterns: List[str], paths: List[str]) -> List[str]
         libraries_by_path = (
             libraries_in_ld_and_system_library_path(path_hints=paths)
             if sys.platform != "win32"
-            else libraries_in_windows_paths(paths)
+            else libraries_in_windows_paths(path_hints=paths)
         )
         patterns = [re.compile(x) for x in patterns]
         result = []
@@ -334,21 +413,16 @@ def by_path(
     # TODO: Packages should be able to define both .libraries and .executables in the future
     # TODO: determine_spec_details should get all relevant libraries and executables in one call
     executables_finder, libraries_finder = ExecutablesFinder(), LibrariesFinder()
-
-    executables_path_guess = (
-        spack.util.environment.get_path("PATH") if path_hints is None else path_hints
-    )
-    libraries_path_guess = [] if path_hints is None else path_hints
     detected_specs_by_package: Dict[str, Tuple[concurrent.futures.Future, ...]] = {}
 
     result = collections.defaultdict(list)
     with concurrent.futures.ProcessPoolExecutor(max_workers=max_workers) as executor:
         for pkg in packages_to_search:
             executable_future = executor.submit(
-                executables_finder.find, pkg_name=pkg, initial_guess=executables_path_guess
+                executables_finder.find, pkg_name=pkg, initial_guess=path_hints
             )
             library_future = executor.submit(
-                libraries_finder.find, pkg_name=pkg, initial_guess=libraries_path_guess
+                libraries_finder.find, pkg_name=pkg, initial_guess=path_hints
             )
             detected_specs_by_package[pkg] = executable_future, library_future
 
@@ -359,9 +433,13 @@ def by_path(
                     if detected:
                         _, unqualified_name = spack.repo.partition_package_name(pkg_name)
                         result[unqualified_name].extend(detected)
-                except Exception:
+                except concurrent.futures.TimeoutError:
                     llnl.util.tty.debug(
                         f"[EXTERNAL DETECTION] Skipping {pkg_name}: timeout reached"
                     )
+                except Exception as e:
+                    llnl.util.tty.debug(
+                        f"[EXTERNAL DETECTION] Skipping {pkg_name}: exception occured {e}"
+                    )
 
     return result

lib/spack/spack/directives.py

@@ -137,6 +137,7 @@ class DirectiveMeta(type):
     _directive_dict_names: Set[str] = set()
     _directives_to_be_executed: List[str] = []
     _when_constraints_from_context: List[str] = []
+    _default_args: List[dict] = []
 
     def __new__(cls, name, bases, attr_dict):
         # Initialize the attribute containing the list of directives
@@ -199,6 +200,16 @@ def pop_from_context():
         """Pop the last constraint from the context"""
         return DirectiveMeta._when_constraints_from_context.pop()
 
+    @staticmethod
+    def push_default_args(default_args):
+        """Push default arguments"""
+        DirectiveMeta._default_args.append(default_args)
+
+    @staticmethod
+    def pop_default_args():
+        """Pop default arguments"""
+        return DirectiveMeta._default_args.pop()
+
     @staticmethod
     def directive(dicts=None):
         """Decorator for Spack directives.
@@ -259,7 +270,13 @@ def _decorator(decorated_function):
             directive_names.append(decorated_function.__name__)
 
             @functools.wraps(decorated_function)
-            def _wrapper(*args, **kwargs):
+            def _wrapper(*args, **_kwargs):
+                # First merge default args with kwargs
+                kwargs = dict()
+                for default_args in DirectiveMeta._default_args:
+                    kwargs.update(default_args)
+                kwargs.update(_kwargs)
+
                 # Inject when arguments from the context
                 if DirectiveMeta._when_constraints_from_context:
                     # Check that directives not yet supporting the when= argument
@@ -573,17 +590,21 @@ def _execute_extends(pkg):
     return _execute_extends
 
 
-@directive("provided")
-def provides(*specs, **kwargs):
-    """Allows packages to provide a virtual dependency.  If a package provides
-    'mpi', other packages can declare that they depend on "mpi", and spack
-    can use the providing package to satisfy the dependency.
+@directive(dicts=("provided", "provided_together"))
+def provides(*specs, when: Optional[str] = None):
+    """Allows packages to provide a virtual dependency.
+
+    If a package provides "mpi", other packages can declare that they depend on "mpi",
+    and spack can use the providing package to satisfy the dependency.
+
+    Args:
+        *specs: virtual specs provided by this package
+        when: condition when this provides clause needs to be considered
     """
 
     def _execute_provides(pkg):
         import spack.parser  # Avoid circular dependency
 
-        when = kwargs.get("when")
         when_spec = make_when_spec(when)
         if not when_spec:
             return
@@ -591,15 +612,18 @@ def _execute_provides(pkg):
         # ``when`` specs for ``provides()`` need a name, as they are used
         # to build the ProviderIndex.
         when_spec.name = pkg.name
+        spec_objs = [spack.spec.Spec(x) for x in specs]
+        spec_names = [x.name for x in spec_objs]
+        if len(spec_names) > 1:
+            pkg.provided_together.setdefault(when_spec, []).append(set(spec_names))
 
-        for string in specs:
-            for provided_spec in spack.parser.parse(string):
-                if pkg.name == provided_spec.name:
-                    raise CircularReferenceError("Package '%s' cannot provide itself." % pkg.name)
+        for provided_spec in spec_objs:
+            if pkg.name == provided_spec.name:
+                raise CircularReferenceError("Package '%s' cannot provide itself." % pkg.name)
 
-                if provided_spec not in pkg.provided:
-                    pkg.provided[provided_spec] = set()
-                pkg.provided[provided_spec].add(when_spec)
+            if provided_spec not in pkg.provided:
+                pkg.provided[provided_spec] = set()
+            pkg.provided[provided_spec].add(when_spec)
 
     return _execute_provides
 

lib/spack/spack/environment/__init__.py

@@ -339,6 +339,7 @@
 from .environment import (
     TOP_LEVEL_KEY,
     Environment,
+    SpackEnvironmentConfigError,
     SpackEnvironmentError,
     SpackEnvironmentViewError,
     activate,
@@ -372,6 +373,7 @@
 __all__ = [
     "TOP_LEVEL_KEY",
     "Environment",
+    "SpackEnvironmentConfigError",
     "SpackEnvironmentError",
     "SpackEnvironmentViewError",
     "activate",

lib/spack/spack/environment/depfile.py

@@ -232,6 +232,10 @@ def to_dict(self):
             "pkg_ids": " ".join(self.all_pkg_identifiers),
         }
 
+    @property
+    def empty(self):
+        return len(self.roots) == 0
+
     @staticmethod
     def from_env(
         env: ev.Environment,
@@ -254,15 +258,10 @@ def from_env(
             jobserver: when enabled, make will invoke Spack with jobserver support. For
                 dry-run this should be disabled.
         """
-        # If no specs are provided as a filter, build all the specs in the environment.
-        if filter_specs:
-            entrypoints = [env.matching_spec(s) for s in filter_specs]
-        else:
-            entrypoints = [s for _, s in env.concretized_specs()]
-
+        roots = env.all_matching_specs(*filter_specs) if filter_specs else env.concrete_roots()
         visitor = DepfileSpecVisitor(pkg_buildcache, dep_buildcache)
         traverse.traverse_breadth_first_with_visitor(
-            entrypoints, traverse.CoverNodesVisitor(visitor, key=lambda s: s.dag_hash())
+            roots, traverse.CoverNodesVisitor(visitor, key=lambda s: s.dag_hash())
         )
 
-        return MakefileModel(env, entrypoints, visitor.adjacency_list, make_prefix, jobserver)
+        return MakefileModel(env, roots, visitor.adjacency_list, make_prefix, jobserver)

lib/spack/spack/environment/environment.py

@@ -330,16 +330,21 @@ def create_in_dir(
     if with_view is None and keep_relative:
         return Environment(manifest_dir)
 
-    manifest = EnvironmentManifestFile(manifest_dir)
+    try:
+        manifest = EnvironmentManifestFile(manifest_dir)
 
-    if with_view is not None:
-        manifest.set_default_view(with_view)
+        if with_view is not None:
+            manifest.set_default_view(with_view)
 
-    if not keep_relative and init_file is not None and str(init_file).endswith(manifest_name):
-        init_file = pathlib.Path(init_file)
-        manifest.absolutify_dev_paths(init_file.parent)
+        if not keep_relative and init_file is not None and str(init_file).endswith(manifest_name):
+            init_file = pathlib.Path(init_file)
+            manifest.absolutify_dev_paths(init_file.parent)
 
-    manifest.flush()
+        manifest.flush()
+
+    except (spack.config.ConfigFormatError, SpackEnvironmentConfigError) as e:
+        shutil.rmtree(manifest_dir)
+        raise e
 
     return Environment(manifest_dir)
 
@@ -391,7 +396,13 @@ def all_environments():
 
 def _read_yaml(str_or_file):
     """Read YAML from a file for round-trip parsing."""
-    data = syaml.load_config(str_or_file)
+    try:
+        data = syaml.load_config(str_or_file)
+    except syaml.SpackYAMLError as e:
+        raise SpackEnvironmentConfigError(
+            f"Invalid environment configuration detected: {e.message}"
+        )
+
     filename = getattr(str_or_file, "name", None)
     default_data = spack.config.validate(data, spack.schema.env.schema, filename)
     return data, default_data
@@ -776,10 +787,18 @@ def _re_read(self):
         """Reinitialize the environment object."""
         self.clear(re_read=True)
         self.manifest = EnvironmentManifestFile(self.path)
-        self._read()
+        self._read(re_read=True)
 
-    def _read(self):
-        self._construct_state_from_manifest()
+    def _read(self, re_read=False):
+        # If the manifest has included files, then some of the information
+        # (e.g., definitions) MAY be in those files. So we need to ensure
+        # the config is populated with any associated spec lists in order
+        # to fully construct the manifest state.
+        includes = self.manifest[TOP_LEVEL_KEY].get("include", [])
+        if includes and not re_read:
+            prepare_config_scope(self)
+
+        self._construct_state_from_manifest(re_read)
 
         if os.path.exists(self.lock_path):
             with open(self.lock_path) as f:
@@ -793,21 +812,30 @@ def write_transaction(self):
         """Get a write lock context manager for use in a `with` block."""
         return lk.WriteTransaction(self.txlock, acquire=self._re_read)
 
-    def _construct_state_from_manifest(self):
+    def _process_definition(self, item):
+        """Process a single spec definition item."""
+        entry = copy.deepcopy(item)
+        when = _eval_conditional(entry.pop("when", "True"))
+        assert len(entry) == 1
+        if when:
+            name, spec_list = next(iter(entry.items()))
+            user_specs = SpecList(name, spec_list, self.spec_lists.copy())
+            if name in self.spec_lists:
+                self.spec_lists[name].extend(user_specs)
+            else:
+                self.spec_lists[name] = user_specs
+
+    def _construct_state_from_manifest(self, re_read=False):
         """Read manifest file and set up user specs."""
         self.spec_lists = collections.OrderedDict()
+
+        if not re_read:
+            for item in spack.config.get("definitions", []):
+                self._process_definition(item)
+
         env_configuration = self.manifest[TOP_LEVEL_KEY]
         for item in env_configuration.get("definitions", []):
-            entry = copy.deepcopy(item)
-            when = _eval_conditional(entry.pop("when", "True"))
-            assert len(entry) == 1
-            if when:
-                name, spec_list = next(iter(entry.items()))
-                user_specs = SpecList(name, spec_list, self.spec_lists.copy())
-                if name in self.spec_lists:
-                    self.spec_lists[name].extend(user_specs)
-                else:
-                    self.spec_lists[name] = user_specs
+            self._process_definition(item)
 
         spec_list = env_configuration.get(user_speclist_name, [])
         user_specs = SpecList(
@@ -852,7 +880,9 @@ def clear(self, re_read=False):
                 yaml, and need to be maintained when re-reading an existing
                 environment.
         """
-        self.spec_lists = {user_speclist_name: SpecList()}  # specs from yaml
+        self.spec_lists = collections.OrderedDict()
+        self.spec_lists[user_speclist_name] = SpecList()
+
         self.dev_specs = {}  # dev-build specs from yaml
         self.concretized_user_specs = []  # user specs from last concretize
         self.concretized_order = []  # roots of last concretize, in order
@@ -1001,7 +1031,8 @@ def included_config_scopes(self):
 
             elif include_url.scheme:
                 raise ValueError(
-                    "Unsupported URL scheme for environment include: {}".format(config_path)
+                    f"Unsupported URL scheme ({include_url.scheme}) for "
+                    f"environment include: {config_path}"
                 )
 
             # treat relative paths as relative to the environment
@@ -1063,8 +1094,10 @@ def update_stale_references(self, from_list=None):
             from_list = next(iter(self.spec_lists.keys()))
         index = list(self.spec_lists.keys()).index(from_list)
 
-        # spec_lists is an OrderedDict, all list entries after the modified
-        # list may refer to the modified list. Update stale references
+        # spec_lists is an OrderedDict to ensure lists read from the manifest
+        # are maintainted in order, hence, all list entries after the modified
+        # list may refer to the modified list requiring stale references to be
+        # updated.
         for i, (name, speclist) in enumerate(
             list(self.spec_lists.items())[index + 1 :], index + 1
         ):
@@ -1162,7 +1195,7 @@ def change_existing_spec(
     def remove(self, query_spec, list_name=user_speclist_name, force=False):
         """Remove specs from an environment that match a query_spec"""
         err_msg_header = (
-            f"cannot remove {query_spec} from '{list_name}' definition "
+            f"Cannot remove '{query_spec}' from '{list_name}' definition "
             f"in {self.manifest.manifest_file}"
         )
         query_spec = Spec(query_spec)
@@ -1193,11 +1226,10 @@ def remove(self, query_spec, list_name=user_speclist_name, force=False):
                 list_to_change.remove(spec)
                 self.update_stale_references(list_name)
                 new_specs = set(self.user_specs)
-            except spack.spec_list.SpecListError:
+            except spack.spec_list.SpecListError as e:
                 # define new specs list
                 new_specs = set(self.user_specs)
-                msg = f"Spec '{spec}' is part of a spec matrix and "
-                msg += f"cannot be removed from list '{list_to_change}'."
+                msg = str(e)
                 if force:
                     msg += " It will be removed from the concrete specs."
                     # Mock new specs, so we can remove this spec from concrete spec lists
@@ -1326,7 +1358,7 @@ def concretize(self, force=False, tests=False):
 
         # Remove concrete specs that no longer correlate to a user spec
         for spec in set(self.concretized_user_specs) - set(self.user_specs):
-            self.deconcretize(spec)
+            self.deconcretize(spec, concrete=False)
 
         # Pick the right concretization strategy
         if self.unify == "when_possible":
@@ -1341,15 +1373,36 @@ def concretize(self, force=False, tests=False):
         msg = "concretization strategy not implemented [{0}]"
         raise SpackEnvironmentError(msg.format(self.unify))
 
-    def deconcretize(self, spec):
+    def deconcretize(self, spec: spack.spec.Spec, concrete: bool = True):
+        """
+        Remove specified spec from environment concretization
+
+        Arguments:
+            spec: Spec to deconcretize. This must be a root of the environment
+            concrete: If True, find all instances of spec as concrete in the environemnt.
+                If False, find a single instance of the abstract spec as root of the environment.
+        """
         # spec has to be a root of the environment
-        index = self.concretized_user_specs.index(spec)
-        dag_hash = self.concretized_order.pop(index)
-        del self.concretized_user_specs[index]
+        if concrete:
+            dag_hash = spec.dag_hash()
+
+            pairs = zip(self.concretized_user_specs, self.concretized_order)
+            filtered = [(spec, h) for spec, h in pairs if h != dag_hash]
+            # Cannot use zip and unpack two values; it fails if filtered is empty
+            self.concretized_user_specs = [s for s, _ in filtered]
+            self.concretized_order = [h for _, h in filtered]
+        else:
+            index = self.concretized_user_specs.index(spec)
+            dag_hash = self.concretized_order.pop(index)
+
+            del self.concretized_user_specs[index]
 
         # If this was the only user spec that concretized to this concrete spec, remove it
         if dag_hash not in self.concretized_order:
-            del self.specs_by_hash[dag_hash]
+            # if we deconcretized a dependency that doesn't correspond to a root, it
+            # won't be here.
+            if dag_hash in self.specs_by_hash:
+                del self.specs_by_hash[dag_hash]
 
     def _get_specs_to_concretize(
         self,
@@ -1484,7 +1537,7 @@ def _concretize_separately(self, tests=False):
         for uspec, uspec_constraints in zip(self.user_specs, self.user_specs.specs_as_constraints):
             if uspec not in old_concretized_user_specs:
                 root_specs.append(uspec)
-                args.append((i, uspec_constraints, tests))
+                args.append((i, [str(x) for x in uspec_constraints], tests))
                 i += 1
 
         # Ensure we don't try to bootstrap clingo in parallel
@@ -1518,11 +1571,21 @@ def _concretize_separately(self, tests=False):
         tty.msg(msg)
 
         batch = []
-        for i, concrete, duration in spack.util.parallel.imap_unordered(
-            _concretize_task, args, processes=num_procs, debug=tty.is_debug()
+        for j, (i, concrete, duration) in enumerate(
+            spack.util.parallel.imap_unordered(
+                _concretize_task,
+                args,
+                processes=num_procs,
+                debug=tty.is_debug(),
+                maxtaskperchild=1,
+            )
         ):
             batch.append((i, concrete))
-            tty.verbose(f"[{duration:7.2f}s] {root_specs[i]}")
+            percentage = (j + 1) / len(args) * 100
+            tty.verbose(
+                f"{duration:6.1f}s [{percentage:3.0f}%] {concrete.cformat('{hash:7}')} "
+                f"{root_specs[i].colored_str}"
+            )
             sys.stdout.flush()
 
         # Add specs in original order
@@ -1697,11 +1760,14 @@ def _env_modifications_for_view(
         self, view: ViewDescriptor, reverse: bool = False
     ) -> spack.util.environment.EnvironmentModifications:
         try:
-            mods = uenv.environment_modifications_for_specs(*self.concrete_roots(), view=view)
+            with spack.store.STORE.db.read_transaction():
+                installed_roots = [s for s in self.concrete_roots() if s.installed]
+            mods = uenv.environment_modifications_for_specs(*installed_roots, view=view)
         except Exception as e:
             # Failing to setup spec-specific changes shouldn't be a hard error.
             tty.warn(
-                "couldn't load runtime environment due to {}: {}".format(e.__class__.__name__, e)
+                f"could not {'unload' if reverse else 'load'} runtime environment due "
+                f"to {e.__class__.__name__}: {e}"
             )
             return spack.util.environment.EnvironmentModifications()
         return mods.reversed() if reverse else mods
@@ -2052,7 +2118,7 @@ def matching_spec(self, spec):
 
     def removed_specs(self):
         """Tuples of (user spec, concrete spec) for all specs that will be
-        removed on nexg concretize."""
+        removed on next concretize."""
         needed = set()
         for s, c in self.concretized_specs():
             if s in self.user_specs:
@@ -2397,6 +2463,7 @@ def _concretize_from_constraints(spec_constraints, tests=False):
 
 def _concretize_task(packed_arguments) -> Tuple[int, Spec, float]:
     index, spec_constraints, tests = packed_arguments
+    spec_constraints = [Spec(x) for x in spec_constraints]
     with tty.SuppressOutput(msg_enabled=False):
         start = time.time()
         spec = _concretize_from_constraints(spec_constraints, tests)
@@ -2710,7 +2777,7 @@ def override_user_spec(self, user_spec: str, idx: int) -> None:
         self.changed = True
 
     def add_definition(self, user_spec: str, list_name: str) -> None:
-        """Appends a user spec to the first active definition mathing the name passed as argument.
+        """Appends a user spec to the first active definition matching the name passed as argument.
 
         Args:
             user_spec: user spec to be appended
@@ -2923,3 +2990,7 @@ class SpackEnvironmentError(spack.error.SpackError):
 
 class SpackEnvironmentViewError(SpackEnvironmentError):
     """Class for errors regarding view generation."""
+
+
+class SpackEnvironmentConfigError(SpackEnvironmentError):
+    """Class for Spack environment-specific configuration errors."""

lib/spack/spack/extensions.py

@@ -5,6 +5,7 @@
 """Service functions and classes to implement the hooks
 for Spack's command extensions.
 """
+import difflib
 import importlib
 import os
 import re
@@ -176,10 +177,19 @@ class CommandNotFoundError(spack.error.SpackError):
     """
 
     def __init__(self, cmd_name):
-        super().__init__(
+        msg = (
             "{0} is not a recognized Spack command or extension command;"
             " check with `spack commands`.".format(cmd_name)
         )
+        long_msg = None
+
+        similar = difflib.get_close_matches(cmd_name, spack.cmd.all_commands())
+
+        if 1 <= len(similar) <= 5:
+            long_msg = "\nDid you mean one of the following commands?\n  "
+            long_msg += "\n  ".join(similar)
+
+        super().__init__(msg, long_msg)
 
 
 class ExtensionNamingError(spack.error.SpackError):

lib/spack/spack/fetch_strategy.py

@@ -28,6 +28,7 @@
 import os.path
 import re
 import shutil
+import urllib.error
 import urllib.parse
 from typing import List, Optional
 
@@ -41,6 +42,7 @@
 
 import spack.config
 import spack.error
+import spack.oci.opener
 import spack.url
 import spack.util.crypto as crypto
 import spack.util.git
@@ -537,6 +539,34 @@ def fetch(self):
         tty.msg("Using cached archive: {0}".format(path))
 
 
+class OCIRegistryFetchStrategy(URLFetchStrategy):
+    def __init__(self, url=None, checksum=None, **kwargs):
+        super().__init__(url, checksum, **kwargs)
+
+        self._urlopen = kwargs.get("_urlopen", spack.oci.opener.urlopen)
+
+    @_needs_stage
+    def fetch(self):
+        file = self.stage.save_filename
+        tty.msg(f"Fetching {self.url}")
+
+        try:
+            response = self._urlopen(self.url)
+        except urllib.error.URLError as e:
+            # clean up archive on failure.
+            if self.archive_file:
+                os.remove(self.archive_file)
+            if os.path.lexists(file):
+                os.remove(file)
+            raise FailedDownloadError(self.url, f"Failed to fetch {self.url}: {e}") from e
+
+        if os.path.lexists(file):
+            os.remove(file)
+
+        with open(file, "wb") as f:
+            shutil.copyfileobj(response, f)
+
+
 class VCSFetchStrategy(FetchStrategy):
     """Superclass for version control system fetch strategies.
 
@@ -743,8 +773,7 @@ def git(self):
             # Disable advice for a quieter fetch
             # https://github.com/git/git/blob/master/Documentation/RelNotes/1.7.2.txt
             if self.git_version >= spack.version.Version("1.7.2"):
-                self._git.add_default_arg("-c")
-                self._git.add_default_arg("advice.detachedHead=false")
+                self._git.add_default_arg("-c", "advice.detachedHead=false")
 
             # If the user asked for insecure fetching, make that work
             # with git as well.

lib/spack/spack/graph.py

@@ -528,10 +528,15 @@ def node_entry(self, node):
 
     def edge_entry(self, edge):
         colormap = {"build": "dodgerblue", "link": "crimson", "run": "goldenrod"}
+        label = ""
+        if edge.virtuals:
+            label = f" xlabel=\"virtuals={','.join(edge.virtuals)}\""
         return (
             edge.parent.dag_hash(),
             edge.spec.dag_hash(),
-            f"[color=\"{':'.join(colormap[x] for x in dt.flag_to_tuple(edge.depflag))}\"]",
+            f"[color=\"{':'.join(colormap[x] for x in dt.flag_to_tuple(edge.depflag))}\""
+            + label
+            + "]",
         )
 
 

lib/spack/spack/hooks/module_file_generation.py

@@ -3,17 +3,22 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+from typing import Optional, Set
+
 from llnl.util import tty
 
 import spack.config
 import spack.modules
+import spack.spec
 
 
-def _for_each_enabled(spec, method_name, explicit=None):
+def _for_each_enabled(
+    spec: spack.spec.Spec, method_name: str, explicit: Optional[bool] = None
+) -> None:
     """Calls a method for each enabled module"""
-    set_names = set(spack.config.get("modules", {}).keys())
+    set_names: Set[str] = set(spack.config.get("modules", {}).keys())
     for name in set_names:
-        enabled = spack.config.get("modules:%s:enable" % name)
+        enabled = spack.config.get(f"modules:{name}:enable")
         if not enabled:
             tty.debug("NO MODULE WRITTEN: list of enabled module files is empty")
             continue
@@ -28,7 +33,7 @@ def _for_each_enabled(spec, method_name, explicit=None):
                 tty.warn(msg.format(method_name, str(e)))
 
 
-def post_install(spec, explicit):
+def post_install(spec, explicit: bool):
     import spack.environment as ev  # break import cycle
 
     if ev.active_environment():

lib/spack/spack/main.py

@@ -16,11 +16,13 @@
 import os.path
 import pstats
 import re
+import shlex
 import signal
 import subprocess as sp
 import sys
 import traceback
 import warnings
+from typing import List, Tuple
 
 import archspec.cpu
 
@@ -49,9 +51,6 @@
 #: names of profile statistics
 stat_names = pstats.Stats.sort_arg_dict_default
 
-#: top-level aliases for Spack commands
-aliases = {"concretise": "concretize", "containerise": "containerize", "rm": "remove"}
-
 #: help levels in order of detail (i.e., number of commands shown)
 levels = ["short", "long"]
 
@@ -359,7 +358,10 @@ def add_command(self, cmd_name):
             module = spack.cmd.get_module(cmd_name)
 
             # build a list of aliases
-            alias_list = [k for k, v in aliases.items() if v == cmd_name]
+            alias_list = []
+            aliases = spack.config.get("config:aliases")
+            if aliases:
+                alias_list = [k for k, v in aliases.items() if shlex.split(v)[0] == cmd_name]
 
             subparser = self.subparsers.add_parser(
                 cmd_name,
@@ -670,7 +672,6 @@ def __init__(self, command_name, subprocess=False):
                 Windows, where it is always False.
         """
         self.parser = make_argument_parser()
-        self.command = self.parser.add_command(command_name)
         self.command_name = command_name
         # TODO: figure out how to support this on windows
         self.subprocess = subprocess if sys.platform != "win32" else False
@@ -702,13 +703,14 @@ def __call__(self, *argv, **kwargs):
 
         if self.subprocess:
             p = sp.Popen(
-                [spack.paths.spack_script, self.command_name] + prepend + list(argv),
+                [spack.paths.spack_script] + prepend + [self.command_name] + list(argv),
                 stdout=sp.PIPE,
                 stderr=sp.STDOUT,
             )
             out, self.returncode = p.communicate()
             out = out.decode()
         else:
+            command = self.parser.add_command(self.command_name)
             args, unknown = self.parser.parse_known_args(
                 prepend + [self.command_name] + list(argv)
             )
@@ -716,7 +718,7 @@ def __call__(self, *argv, **kwargs):
             out = io.StringIO()
             try:
                 with log_output(out, echo=True):
-                    self.returncode = _invoke_command(self.command, self.parser, args, unknown)
+                    self.returncode = _invoke_command(command, self.parser, args, unknown)
 
             except SystemExit as e:
                 self.returncode = e.code
@@ -870,6 +872,46 @@ def restore_macos_dyld_vars():
             os.environ[dyld_var] = os.environ[stored_var_name]
 
 
+def resolve_alias(cmd_name: str, cmd: List[str]) -> Tuple[str, List[str]]:
+    """Resolves aliases in the given command.
+
+    Args:
+        cmd_name: command name.
+        cmd: command line arguments.
+
+    Returns:
+        new command name and arguments.
+    """
+    all_commands = spack.cmd.all_commands()
+    aliases = spack.config.get("config:aliases")
+
+    if aliases:
+        for key, value in aliases.items():
+            if " " in key:
+                tty.warn(
+                    f"Alias '{key}' (mapping to '{value}') contains a space"
+                    ", which is not supported."
+                )
+            if key in all_commands:
+                tty.warn(
+                    f"Alias '{key}' (mapping to '{value}') attempts to override"
+                    " built-in command."
+                )
+
+    if cmd_name not in all_commands:
+        alias = None
+
+        if aliases:
+            alias = aliases.get(cmd_name)
+
+        if alias is not None:
+            alias_parts = shlex.split(alias)
+            cmd_name = alias_parts[0]
+            cmd = alias_parts + cmd[1:]
+
+    return cmd_name, cmd
+
+
 def _main(argv=None):
     """Logic for the main entry point for the Spack command.
 
@@ -962,7 +1004,7 @@ def _main(argv=None):
 
     # Try to load the particular command the caller asked for.
     cmd_name = args.command[0]
-    cmd_name = aliases.get(cmd_name, cmd_name)
+    cmd_name, args.command = resolve_alias(cmd_name, args.command)
 
     # set up a bootstrap context, if asked.
     # bootstrap context needs to include parsing the command, b/c things
@@ -974,10 +1016,10 @@ def _main(argv=None):
         bootstrap_context = bootstrap.ensure_bootstrap_configuration()
 
     with bootstrap_context:
-        return finish_parse_and_run(parser, cmd_name, env_format_error)
+        return finish_parse_and_run(parser, cmd_name, args.command, env_format_error)
 
 
-def finish_parse_and_run(parser, cmd_name, env_format_error):
+def finish_parse_and_run(parser, cmd_name, cmd, env_format_error):
     """Finish parsing after we know the command to run."""
     # add the found command to the parser and re-run then re-parse
     command = parser.add_command(cmd_name)

lib/spack/spack/mirror.py

@@ -18,7 +18,7 @@
 import sys
 import traceback
 import urllib.parse
-from typing import Optional, Union
+from typing import List, Optional, Union
 
 import llnl.url
 import llnl.util.tty as tty
@@ -27,18 +27,18 @@
 import spack.caches
 import spack.config
 import spack.error
-import spack.fetch_strategy as fs
+import spack.fetch_strategy
 import spack.mirror
+import spack.oci.image
 import spack.spec
 import spack.util.path
 import spack.util.spack_json as sjson
 import spack.util.spack_yaml as syaml
 import spack.util.url as url_util
-from spack.util.spack_yaml import syaml_dict
-from spack.version import VersionList
+import spack.version
 
 #: What schemes do we support
-supported_url_schemes = ("file", "http", "https", "sftp", "ftp", "s3", "gs")
+supported_url_schemes = ("file", "http", "https", "sftp", "ftp", "s3", "gs", "oci")
 
 
 def _url_or_path_to_url(url_or_path: str) -> str:
@@ -230,12 +230,12 @@ def _get_value(self, attribute: str, direction: str):
         value = self._data.get(direction, {})
 
         # Return top-level entry if only a URL was set.
-        if isinstance(value, str):
-            return self._data.get(attribute, None)
+        if isinstance(value, str) or attribute not in value:
+            return self._data.get(attribute)
 
-        return self._data.get(direction, {}).get(attribute, None)
+        return value[attribute]
 
-    def get_url(self, direction: str):
+    def get_url(self, direction: str) -> str:
         if direction not in ("fetch", "push"):
             raise ValueError(f"direction must be either 'fetch' or 'push', not {direction}")
 
@@ -255,18 +255,21 @@ def get_url(self, direction: str):
             elif "url" in info:
                 url = info["url"]
 
-        return _url_or_path_to_url(url) if url else None
+        if not url:
+            raise ValueError(f"Mirror {self.name} has no URL configured")
 
-    def get_access_token(self, direction: str):
+        return _url_or_path_to_url(url)
+
+    def get_access_token(self, direction: str) -> Optional[str]:
         return self._get_value("access_token", direction)
 
-    def get_access_pair(self, direction: str):
+    def get_access_pair(self, direction: str) -> Optional[List]:
         return self._get_value("access_pair", direction)
 
-    def get_profile(self, direction: str):
+    def get_profile(self, direction: str) -> Optional[str]:
         return self._get_value("profile", direction)
 
-    def get_endpoint_url(self, direction: str):
+    def get_endpoint_url(self, direction: str) -> Optional[str]:
         return self._get_value("endpoint_url", direction)
 
 
@@ -330,7 +333,7 @@ def from_json(stream, name=None):
             raise sjson.SpackJSONError("error parsing JSON mirror collection:", str(e)) from e
 
     def to_dict(self, recursive=False):
-        return syaml_dict(
+        return syaml.syaml_dict(
             sorted(
                 ((k, (v.to_dict() if recursive else v)) for (k, v) in self._mirrors.items()),
                 key=operator.itemgetter(0),
@@ -372,7 +375,7 @@ def __len__(self):
 
 
 def _determine_extension(fetcher):
-    if isinstance(fetcher, fs.URLFetchStrategy):
+    if isinstance(fetcher, spack.fetch_strategy.URLFetchStrategy):
         if fetcher.expand_archive:
             # If we fetch with a URLFetchStrategy, use URL's archive type
             ext = llnl.url.determine_url_file_extension(fetcher.url)
@@ -437,6 +440,19 @@ def __iter__(self):
         yield self.cosmetic_path
 
 
+class OCIImageLayout:
+    """Follow the OCI Image Layout Specification to archive blobs
+
+    Paths are of the form `blobs/<algorithm>/<digest>`
+    """
+
+    def __init__(self, digest: spack.oci.image.Digest) -> None:
+        self.storage_path = os.path.join("blobs", digest.algorithm, digest.digest)
+
+    def __iter__(self):
+        yield self.storage_path
+
+
 def mirror_archive_paths(fetcher, per_package_ref, spec=None):
     """Returns a ``MirrorReference`` object which keeps track of the relative
     storage path of the resource associated with the specified ``fetcher``."""
@@ -482,7 +498,7 @@ def get_all_versions(specs):
 
         for version in pkg_cls.versions:
             version_spec = spack.spec.Spec(pkg_cls.name)
-            version_spec.versions = VersionList([version])
+            version_spec.versions = spack.version.VersionList([version])
             version_specs.append(version_spec)
 
     return version_specs
@@ -521,7 +537,7 @@ def get_matching_versions(specs, num_versions=1):
             # Generate only versions that satisfy the spec.
             if spec.concrete or v.intersects(spec.versions):
                 s = spack.spec.Spec(pkg.name)
-                s.versions = VersionList([v])
+                s.versions = spack.version.VersionList([v])
                 s.variants = spec.variants.copy()
                 # This is needed to avoid hanging references during the
                 # concretization phase
@@ -591,14 +607,14 @@ def add(mirror: Mirror, scope=None):
     """Add a named mirror in the given scope"""
     mirrors = spack.config.get("mirrors", scope=scope)
     if not mirrors:
-        mirrors = syaml_dict()
+        mirrors = syaml.syaml_dict()
 
     if mirror.name in mirrors:
         tty.die("Mirror with name {} already exists.".format(mirror.name))
 
     items = [(n, u) for n, u in mirrors.items()]
     items.insert(0, (mirror.name, mirror.to_dict()))
-    mirrors = syaml_dict(items)
+    mirrors = syaml.syaml_dict(items)
     spack.config.set("mirrors", mirrors, scope=scope)
 
 
@@ -606,7 +622,7 @@ def remove(name, scope):
     """Remove the named mirror in the given scope"""
     mirrors = spack.config.get("mirrors", scope=scope)
     if not mirrors:
-        mirrors = syaml_dict()
+        mirrors = syaml.syaml_dict()
 
     if name not in mirrors:
         tty.die("No mirror with name %s" % name)

lib/spack/spack/modules/__init__.py

@@ -7,10 +7,15 @@
 include Tcl non-hierarchical modules, Lua hierarchical modules, and others.
 """
 
-from .common import disable_modules
+from typing import Dict, Type
+
+from .common import BaseModuleFileWriter, disable_modules
 from .lmod import LmodModulefileWriter
 from .tcl import TclModulefileWriter
 
 __all__ = ["TclModulefileWriter", "LmodModulefileWriter", "disable_modules"]
 
-module_types = {"tcl": TclModulefileWriter, "lmod": LmodModulefileWriter}
+module_types: Dict[str, Type[BaseModuleFileWriter]] = {
+    "tcl": TclModulefileWriter,
+    "lmod": LmodModulefileWriter,
+}

lib/spack/spack/modules/common.py

@@ -35,7 +35,7 @@
 import os.path
 import re
 import string
-from typing import Optional
+from typing import List, Optional
 
 import llnl.util.filesystem
 import llnl.util.tty as tty
@@ -50,6 +50,7 @@
 import spack.projections as proj
 import spack.repo
 import spack.schema.environment
+import spack.spec
 import spack.store
 import spack.tengine as tengine
 import spack.util.environment
@@ -395,16 +396,14 @@ class BaseConfiguration:
 
     default_projections = {"all": "{name}/{version}-{compiler.name}-{compiler.version}"}
 
-    def __init__(self, spec, module_set_name, explicit=None):
+    def __init__(self, spec: spack.spec.Spec, module_set_name: str, explicit: bool) -> None:
         # Module where type(self) is defined
-        self.module = inspect.getmodule(self)
+        m = inspect.getmodule(self)
+        assert m is not None  # make mypy happy
+        self.module = m
         # Spec for which we want to generate a module file
         self.spec = spec
         self.name = module_set_name
-        # Software installation has been explicitly asked (get this information from
-        # db when querying an existing module, like during a refresh or rm operations)
-        if explicit is None:
-            explicit = spec._installed_explicitly()
         self.explicit = explicit
         # Dictionary of configuration options that should be applied
         # to the spec
@@ -458,7 +457,11 @@ def suffixes(self):
             if constraint in self.spec:
                 suffixes.append(suffix)
         suffixes = list(dedupe(suffixes))
-        if self.hash:
+        # For hidden modules we can always add a fixed length hash as suffix, since it guards
+        # against file name clashes, and the module is not exposed to the user anyways.
+        if self.hidden:
+            suffixes.append(self.spec.dag_hash(length=7))
+        elif self.hash:
             suffixes.append(self.hash)
         return suffixes
 
@@ -483,37 +486,37 @@ def excluded(self):
         spec = self.spec
         conf = self.module.configuration(self.name)
 
-        # Compute the list of include rules that match
-        include_rules = conf.get("include", [])
-        include_matches = [x for x in include_rules if spec.satisfies(x)]
-
-        # Compute the list of exclude rules that match
-        exclude_rules = conf.get("exclude", [])
-        exclude_matches = [x for x in exclude_rules if spec.satisfies(x)]
-
-        # Should I exclude the module because it's implicit?
-        exclude_implicits = conf.get("exclude_implicits", None)
-        excluded_as_implicit = exclude_implicits and not self.explicit
+        # Compute the list of matching include / exclude rules, and whether excluded as implicit
+        include_matches = [x for x in conf.get("include", []) if spec.satisfies(x)]
+        exclude_matches = [x for x in conf.get("exclude", []) if spec.satisfies(x)]
+        excluded_as_implicit = not self.explicit and conf.get("exclude_implicits", False)
 
         def debug_info(line_header, match_list):
             if match_list:
-                msg = "\t{0} : {1}".format(line_header, spec.cshort_spec)
-                tty.debug(msg)
+                tty.debug(f"\t{line_header} : {spec.cshort_spec}")
                 for rule in match_list:
-                    tty.debug("\t\tmatches rule: {0}".format(rule))
+                    tty.debug(f"\t\tmatches rule: {rule}")
 
         debug_info("INCLUDE", include_matches)
         debug_info("EXCLUDE", exclude_matches)
 
         if excluded_as_implicit:
-            msg = "\tEXCLUDED_AS_IMPLICIT : {0}".format(spec.cshort_spec)
-            tty.debug(msg)
+            tty.debug(f"\tEXCLUDED_AS_IMPLICIT : {spec.cshort_spec}")
 
-        is_excluded = exclude_matches or excluded_as_implicit
-        if not include_matches and is_excluded:
-            return True
+        return not include_matches and (exclude_matches or excluded_as_implicit)
 
-        return False
+    @property
+    def hidden(self):
+        """Returns True if the module has been hidden, False otherwise."""
+
+        conf = self.module.configuration(self.name)
+
+        hidden_as_implicit = not self.explicit and conf.get("hide_implicits", False)
+
+        if hidden_as_implicit:
+            tty.debug(f"\tHIDDEN_AS_IMPLICIT : {self.spec.cshort_spec}")
+
+        return hidden_as_implicit
 
     @property
     def context(self):
@@ -543,8 +546,7 @@ def exclude_env_vars(self):
     def _create_list_for(self, what):
         include = []
         for item in self.conf[what]:
-            conf = type(self)(item, self.name)
-            if not conf.excluded:
+            if not self.module.make_configuration(item, self.name).excluded:
                 include.append(item)
         return include
 
@@ -723,7 +725,9 @@ def environment_modifications(self):
         # for that to work, globals have to be set on the package modules, and the
         # whole chain of setup_dependent_package has to be followed from leaf to spec.
         # So: just run it here, but don't collect env mods.
-        spack.build_environment.SetupContext(context=Context.RUN).set_all_package_py_globals()
+        spack.build_environment.SetupContext(
+            spec, context=Context.RUN
+        ).set_all_package_py_globals()
 
         # Then run setup_dependent_run_environment before setup_run_environment.
         for dep in spec.dependencies(deptype=("link", "run")):
@@ -816,8 +820,7 @@ def autoload(self):
     def _create_module_list_of(self, what):
         m = self.conf.module
         name = self.conf.name
-        explicit = self.conf.explicit
-        return [m.make_layout(x, name, explicit).use_name for x in getattr(self.conf, what)]
+        return [m.make_layout(x, name).use_name for x in getattr(self.conf, what)]
 
     @tengine.context_property
     def verbose(self):
@@ -826,12 +829,19 @@ def verbose(self):
 
 
 class BaseModuleFileWriter:
-    def __init__(self, spec, module_set_name, explicit=None):
+    default_template: str
+    hide_cmd_format: str
+    modulerc_header: List[str]
+
+    def __init__(
+        self, spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+    ) -> None:
         self.spec = spec
 
         # This class is meant to be derived. Get the module of the
         # actual writer.
         self.module = inspect.getmodule(self)
+        assert self.module is not None  # make mypy happy
         m = self.module
 
         # Create the triplet of configuration/layout/context
@@ -849,6 +859,26 @@ def __init__(self, spec, module_set_name, explicit=None):
             name = type(self).__name__
             raise DefaultTemplateNotDefined(msg.format(name))
 
+        # Check if format for module hide command has been defined,
+        # throw if not found
+        try:
+            self.hide_cmd_format
+        except AttributeError:
+            msg = "'{0}' object has no attribute 'hide_cmd_format'\n"
+            msg += "Did you forget to define it in the class?"
+            name = type(self).__name__
+            raise HideCmdFormatNotDefined(msg.format(name))
+
+        # Check if modulerc header content has been defined,
+        # throw if not found
+        try:
+            self.modulerc_header
+        except AttributeError:
+            msg = "'{0}' object has no attribute 'modulerc_header'\n"
+            msg += "Did you forget to define it in the class?"
+            name = type(self).__name__
+            raise ModulercHeaderNotDefined(msg.format(name))
+
     def _get_template(self):
         """Gets the template that will be rendered for this spec."""
         # Get templates and put them in the order of importance:
@@ -943,6 +973,9 @@ def write(self, overwrite=False):
         # Symlink defaults if needed
         self.update_module_defaults()
 
+        # record module hiddenness if implicit
+        self.update_module_hiddenness()
+
     def update_module_defaults(self):
         if any(self.spec.satisfies(default) for default in self.conf.defaults):
             # This spec matches a default, it needs to be symlinked to default
@@ -953,6 +986,60 @@ def update_module_defaults(self):
             os.symlink(self.layout.filename, default_tmp)
             os.rename(default_tmp, default_path)
 
+    def update_module_hiddenness(self, remove=False):
+        """Update modulerc file corresponding to module to add or remove
+        command that hides module depending on its hidden state.
+
+        Args:
+            remove (bool): if True, hiddenness information for module is
+                removed from modulerc.
+        """
+        modulerc_path = self.layout.modulerc
+        hide_module_cmd = self.hide_cmd_format % self.layout.use_name
+        hidden = self.conf.hidden and not remove
+        modulerc_exists = os.path.exists(modulerc_path)
+        updated = False
+
+        if modulerc_exists:
+            # retrieve modulerc content
+            with open(modulerc_path, "r") as f:
+                content = f.readlines()
+                content = "".join(content).split("\n")
+                # remove last empty item if any
+                if len(content[-1]) == 0:
+                    del content[-1]
+            already_hidden = hide_module_cmd in content
+
+            # remove hide command if module not hidden
+            if already_hidden and not hidden:
+                content.remove(hide_module_cmd)
+                updated = True
+
+            # add hide command if module is hidden
+            elif not already_hidden and hidden:
+                if len(content) == 0:
+                    content = self.modulerc_header.copy()
+                content.append(hide_module_cmd)
+                updated = True
+        else:
+            content = self.modulerc_header.copy()
+            if hidden:
+                content.append(hide_module_cmd)
+                updated = True
+
+        # no modulerc file change if no content update
+        if updated:
+            is_empty = content == self.modulerc_header or len(content) == 0
+            # remove existing modulerc if empty
+            if modulerc_exists and is_empty:
+                os.remove(modulerc_path)
+            # create or update modulerc
+            elif content != self.modulerc_header:
+                # ensure file ends with a newline character
+                content.append("")
+                with open(modulerc_path, "w") as f:
+                    f.write("\n".join(content))
+
     def remove(self):
         """Deletes the module file."""
         mod_file = self.layout.filename
@@ -960,6 +1047,7 @@ def remove(self):
             try:
                 os.remove(mod_file)  # Remove the module file
                 self.remove_module_defaults()  # Remove default targeting module file
+                self.update_module_hiddenness(remove=True)  # Remove hide cmd in modulerc
                 os.removedirs(
                     os.path.dirname(mod_file)
                 )  # Remove all the empty directories from the leaf up
@@ -1003,5 +1091,17 @@ class DefaultTemplateNotDefined(AttributeError, ModulesError):
     """
 
 
+class HideCmdFormatNotDefined(AttributeError, ModulesError):
+    """Raised if the attribute 'hide_cmd_format' has not been specified
+    in the derived classes.
+    """
+
+
+class ModulercHeaderNotDefined(AttributeError, ModulesError):
+    """Raised if the attribute 'modulerc_header' has not been specified
+    in the derived classes.
+    """
+
+
 class ModulesTemplateNotFoundError(ModulesError, RuntimeError):
     """Raised if the template for a module file was not found."""

lib/spack/spack/modules/lmod.py

@@ -6,8 +6,7 @@
 import collections
 import itertools
 import os.path
-import posixpath
-from typing import Any, Dict, List
+from typing import Dict, List, Optional, Tuple
 
 import llnl.util.filesystem as fs
 import llnl.util.lang as lang
@@ -24,18 +23,19 @@
 
 
 #: lmod specific part of the configuration
-def configuration(module_set_name):
-    config_path = "modules:%s:lmod" % module_set_name
-    config = spack.config.get(config_path, {})
-    return config
+def configuration(module_set_name: str) -> dict:
+    return spack.config.get(f"modules:{module_set_name}:lmod", {})
 
 
 # Caches the configuration {spec_hash: configuration}
-configuration_registry: Dict[str, Any] = {}
+configuration_registry: Dict[Tuple[str, str, bool], BaseConfiguration] = {}
 
 
-def make_configuration(spec, module_set_name, explicit):
+def make_configuration(
+    spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+) -> BaseConfiguration:
     """Returns the lmod configuration for spec"""
+    explicit = bool(spec._installed_explicitly()) if explicit is None else explicit
     key = (spec.dag_hash(), module_set_name, explicit)
     try:
         return configuration_registry[key]
@@ -45,16 +45,18 @@ def make_configuration(spec, module_set_name, explicit):
         )
 
 
-def make_layout(spec, module_set_name, explicit):
+def make_layout(
+    spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+) -> BaseFileLayout:
     """Returns the layout information for spec"""
-    conf = make_configuration(spec, module_set_name, explicit)
-    return LmodFileLayout(conf)
+    return LmodFileLayout(make_configuration(spec, module_set_name, explicit))
 
 
-def make_context(spec, module_set_name, explicit):
+def make_context(
+    spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+) -> BaseContext:
     """Returns the context information for spec"""
-    conf = make_configuration(spec, module_set_name, explicit)
-    return LmodContext(conf)
+    return LmodContext(make_configuration(spec, module_set_name, explicit))
 
 
 def guess_core_compilers(name, store=False) -> List[spack.spec.CompilerSpec]:
@@ -97,10 +99,7 @@ def guess_core_compilers(name, store=False) -> List[spack.spec.CompilerSpec]:
 class LmodConfiguration(BaseConfiguration):
     """Configuration class for lmod module files."""
 
-    # Note: Posixpath is used here as well as below as opposed to
-    # os.path.join due to spack.spec.Spec.format
-    # requiring forward slash path seperators at this stage
-    default_projections = {"all": posixpath.join("{name}", "{version}")}
+    default_projections = {"all": "{name}/{version}"}
 
     @property
     def core_compilers(self) -> List[spack.spec.CompilerSpec]:
@@ -232,6 +231,13 @@ def missing(self):
         """Returns the list of tokens that are not available."""
         return [x for x in self.hierarchy_tokens if x not in self.available]
 
+    @property
+    def hidden(self):
+        # Never hide a module that opens a hierarchy
+        if any(self.spec.package.provides(x) for x in self.hierarchy_tokens):
+            return False
+        return super().hidden
+
 
 class LmodFileLayout(BaseFileLayout):
     """File layout for lmod module files."""
@@ -267,12 +273,16 @@ def filename(self):
         hierarchy_name = os.path.join(*parts)
 
         # Compute the absolute path
-        fullname = os.path.join(
+        return os.path.join(
             self.arch_dirname,  # root for lmod files on this architecture
             hierarchy_name,  # relative path
-            ".".join([self.use_name, self.extension]),  # file name
+            f"{self.use_name}.{self.extension}",  # file name
         )
-        return fullname
+
+    @property
+    def modulerc(self):
+        """Returns the modulerc file associated with current module file"""
+        return os.path.join(os.path.dirname(self.filename), f".modulerc.{self.extension}")
 
     def token_to_path(self, name, value):
         """Transforms a hierarchy token into the corresponding path part.
@@ -305,9 +315,7 @@ def path_part_fmt(token):
         # we need to append a hash to the version to distinguish
         # among flavors of the same library (e.g. openblas~openmp vs.
         # openblas+openmp)
-        path = path_part_fmt(token=value)
-        path = "-".join([path, value.dag_hash(length=7)])
-        return path
+        return f"{path_part_fmt(token=value)}-{value.dag_hash(length=7)}"
 
     @property
     def available_path_parts(self):
@@ -319,8 +327,7 @@ def available_path_parts(self):
         # List of services that are part of the hierarchy
         hierarchy = self.conf.hierarchy_tokens
         # Tokenize each part that is both in the hierarchy and available
-        parts = [self.token_to_path(x, available[x]) for x in hierarchy if x in available]
-        return parts
+        return [self.token_to_path(x, available[x]) for x in hierarchy if x in available]
 
     @property
     @lang.memoized
@@ -438,7 +445,7 @@ def missing(self):
     @lang.memoized
     def unlocked_paths(self):
         """Returns the list of paths that are unlocked unconditionally."""
-        layout = make_layout(self.spec, self.conf.name, self.conf.explicit)
+        layout = make_layout(self.spec, self.conf.name)
         return [os.path.join(*parts) for parts in layout.unlocked_paths[None]]
 
     @tengine.context_property
@@ -446,7 +453,7 @@ def conditionally_unlocked_paths(self):
         """Returns the list of paths that are unlocked conditionally.
         Each item in the list is a tuple with the structure (condition, path).
         """
-        layout = make_layout(self.spec, self.conf.name, self.conf.explicit)
+        layout = make_layout(self.spec, self.conf.name)
         value = []
         conditional_paths = layout.unlocked_paths
         conditional_paths.pop(None)
@@ -468,7 +475,11 @@ def manipulate_path(token):
 class LmodModulefileWriter(BaseModuleFileWriter):
     """Writer class for lmod module files."""
 
-    default_template = posixpath.join("modules", "modulefile.lua")
+    default_template = "modules/modulefile.lua"
+
+    modulerc_header = []
+
+    hide_cmd_format = 'hide_version("%s")'
 
 
 class CoreCompilersNotFoundError(spack.error.SpackError, KeyError):

lib/spack/spack/modules/tcl.py

@@ -6,28 +6,30 @@
 """This module implements the classes necessary to generate Tcl
 non-hierarchical modules.
 """
-import posixpath
-from typing import Any, Dict
+import os.path
+from typing import Dict, Optional, Tuple
 
 import spack.config
+import spack.spec
 import spack.tengine as tengine
 
 from .common import BaseConfiguration, BaseContext, BaseFileLayout, BaseModuleFileWriter
 
 
 #: Tcl specific part of the configuration
-def configuration(module_set_name):
-    config_path = "modules:%s:tcl" % module_set_name
-    config = spack.config.get(config_path, {})
-    return config
+def configuration(module_set_name: str) -> dict:
+    return spack.config.get(f"modules:{module_set_name}:tcl", {})
 
 
 # Caches the configuration {spec_hash: configuration}
-configuration_registry: Dict[str, Any] = {}
+configuration_registry: Dict[Tuple[str, str, bool], BaseConfiguration] = {}
 
 
-def make_configuration(spec, module_set_name, explicit):
+def make_configuration(
+    spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+) -> BaseConfiguration:
     """Returns the tcl configuration for spec"""
+    explicit = bool(spec._installed_explicitly()) if explicit is None else explicit
     key = (spec.dag_hash(), module_set_name, explicit)
     try:
         return configuration_registry[key]
@@ -37,16 +39,18 @@ def make_configuration(spec, module_set_name, explicit):
         )
 
 
-def make_layout(spec, module_set_name, explicit):
+def make_layout(
+    spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+) -> BaseFileLayout:
     """Returns the layout information for spec"""
-    conf = make_configuration(spec, module_set_name, explicit)
-    return TclFileLayout(conf)
+    return TclFileLayout(make_configuration(spec, module_set_name, explicit))
 
 
-def make_context(spec, module_set_name, explicit):
+def make_context(
+    spec: spack.spec.Spec, module_set_name: str, explicit: Optional[bool] = None
+) -> BaseContext:
     """Returns the context information for spec"""
-    conf = make_configuration(spec, module_set_name, explicit)
-    return TclContext(conf)
+    return TclContext(make_configuration(spec, module_set_name, explicit))
 
 
 class TclConfiguration(BaseConfiguration):
@@ -56,6 +60,11 @@ class TclConfiguration(BaseConfiguration):
 class TclFileLayout(BaseFileLayout):
     """File layout for tcl module files."""
 
+    @property
+    def modulerc(self):
+        """Returns the modulerc file associated with current module file"""
+        return os.path.join(os.path.dirname(self.filename), ".modulerc")
+
 
 class TclContext(BaseContext):
     """Context class for tcl module files."""
@@ -69,7 +78,8 @@ def prerequisites(self):
 class TclModulefileWriter(BaseModuleFileWriter):
     """Writer class for tcl module files."""
 
-    # Note: Posixpath is used here as opposed to
-    # os.path.join due to spack.spec.Spec.format
-    # requiring forward slash path seperators at this stage
-    default_template = posixpath.join("modules", "modulefile.tcl")
+    default_template = "modules/modulefile.tcl"
+
+    modulerc_header = ["#%Module4.7"]
+
+    hide_cmd_format = "module-hide --soft --hidden-loaded %s"

lib/spack/spack/multimethod.py

@@ -26,6 +26,7 @@
 """
 import functools
 import inspect
+from contextlib import contextmanager
 
 from llnl.util.lang import caller_locals
 
@@ -271,6 +272,13 @@ def __exit__(self, exc_type, exc_val, exc_tb):
         spack.directives.DirectiveMeta.pop_from_context()
 
 
+@contextmanager
+def default_args(**kwargs):
+    spack.directives.DirectiveMeta.push_default_args(kwargs)
+    yield
+    spack.directives.DirectiveMeta.pop_default_args()
+
+
 class MultiMethodError(spack.error.SpackError):
     """Superclass for multimethod dispatch errors"""
 

lib/spack/spack/oci/__init__.py

@@ -0,0 +1,4 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)

lib/spack/spack/oci/image.py

@@ -0,0 +1,235 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import re
+import urllib.parse
+from typing import Optional, Union
+
+import spack.spec
+
+# notice: Docker is more strict (no uppercase allowed). We parse image names *with* uppercase
+# and normalize, so: example.com/Organization/Name -> example.com/organization/name. Tags are
+# case sensitive though.
+alphanumeric_with_uppercase = r"[a-zA-Z0-9]+"
+separator = r"(?:[._]|__|[-]+)"
+localhost = r"localhost"
+domainNameComponent = r"(?:[a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])"
+optionalPort = r"(?::[0-9]+)?"
+tag = r"[\w][\w.-]{0,127}"
+digestPat = r"[A-Za-z][A-Za-z0-9]*(?:[-_+.][A-Za-z][A-Za-z0-9]*)*[:][0-9a-fA-F]{32,}"
+ipv6address = r"\[(?:[a-fA-F0-9:]+)\]"
+
+# domain name
+domainName = rf"{domainNameComponent}(?:\.{domainNameComponent})*"
+host = rf"(?:{domainName}|{ipv6address})"
+domainAndPort = rf"{host}{optionalPort}"
+
+# image name
+pathComponent = rf"{alphanumeric_with_uppercase}(?:{separator}{alphanumeric_with_uppercase})*"
+remoteName = rf"{pathComponent}(?:\/{pathComponent})*"
+namePat = rf"(?:{domainAndPort}\/)?{remoteName}"
+
+# Regex for a full image reference, with 3 groups: name, tag, digest
+referencePat = re.compile(rf"^({namePat})(?::({tag}))?(?:@({digestPat}))?$")
+
+# Regex for splitting the name into domain and path components
+anchoredNameRegexp = re.compile(rf"^(?:({domainAndPort})\/)?({remoteName})$")
+
+
+def ensure_sha256_checksum(oci_blob: str):
+    """Validate that the reference is of the format sha256:<checksum>
+    Return the checksum if valid, raise ValueError otherwise."""
+    if ":" not in oci_blob:
+        raise ValueError(f"Invalid OCI blob format: {oci_blob}")
+    alg, checksum = oci_blob.split(":", 1)
+    if alg != "sha256":
+        raise ValueError(f"Unsupported OCI blob checksum algorithm: {alg}")
+    if len(checksum) != 64:
+        raise ValueError(f"Invalid OCI blob checksum length: {len(checksum)}")
+    return checksum
+
+
+class Digest:
+    """Represents a digest in the format <algorithm>:<digest>.
+    Currently only supports sha256 digests."""
+
+    __slots__ = ["algorithm", "digest"]
+
+    def __init__(self, *, algorithm: str, digest: str) -> None:
+        self.algorithm = algorithm
+        self.digest = digest
+
+    def __eq__(self, __value: object) -> bool:
+        if not isinstance(__value, Digest):
+            return NotImplemented
+        return self.algorithm == __value.algorithm and self.digest == __value.digest
+
+    @classmethod
+    def from_string(cls, string: str) -> "Digest":
+        return cls(algorithm="sha256", digest=ensure_sha256_checksum(string))
+
+    @classmethod
+    def from_sha256(cls, digest: str) -> "Digest":
+        return cls(algorithm="sha256", digest=digest)
+
+    def __str__(self) -> str:
+        return f"{self.algorithm}:{self.digest}"
+
+
+class ImageReference:
+    """A parsed image of the form domain/name:tag[@digest].
+    The digest is optional, and domain and tag are automatically
+    filled out with defaults when parsed from string."""
+
+    __slots__ = ["domain", "name", "tag", "digest"]
+
+    def __init__(
+        self, *, domain: str, name: str, tag: str = "latest", digest: Optional[Digest] = None
+    ):
+        self.domain = domain
+        self.name = name
+        self.tag = tag
+        self.digest = digest
+
+    @classmethod
+    def from_string(cls, string) -> "ImageReference":
+        match = referencePat.match(string)
+        if not match:
+            raise ValueError(f"Invalid image reference: {string}")
+
+        image, tag, digest = match.groups()
+
+        assert isinstance(image, str)
+        assert isinstance(tag, (str, type(None)))
+        assert isinstance(digest, (str, type(None)))
+
+        match = anchoredNameRegexp.match(image)
+
+        # This can never happen, since the regex is implied
+        # by the regex above. It's just here to make mypy happy.
+        assert match, f"Invalid image reference: {string}"
+
+        domain, name = match.groups()
+
+        assert isinstance(domain, (str, type(None)))
+        assert isinstance(name, str)
+
+        # Fill out defaults like docker would do...
+        # Based on github.com/distribution/distribution: allow short names like "ubuntu"
+        # and "user/repo" to be interpreted as "library/ubuntu" and "user/repo:latest
+        # Not sure if Spack should follow Docker, but it's what people expect...
+        if not domain:
+            domain = "index.docker.io"
+            name = f"library/{name}"
+        elif (
+            "." not in domain
+            and ":" not in domain
+            and domain != "localhost"
+            and domain == domain.lower()
+        ):
+            name = f"{domain}/{name}"
+            domain = "index.docker.io"
+
+        # Lowercase the image name. This is enforced by Docker, although the OCI spec isn't clear?
+        # We do this anyways, cause for example in Github Actions the <organization>/<repository>
+        # part can have uppercase, and may be interpolated when specifying the relevant OCI image.
+        name = name.lower()
+
+        if not tag:
+            tag = "latest"
+
+        # sha256 is currently the only algorithm that
+        # we implement, even though the spec allows for more
+        if isinstance(digest, str):
+            digest = Digest.from_string(digest)
+
+        return cls(domain=domain, name=name, tag=tag, digest=digest)
+
+    def manifest_url(self) -> str:
+        digest_or_tag = self.digest or self.tag
+        return f"https://{self.domain}/v2/{self.name}/manifests/{digest_or_tag}"
+
+    def blob_url(self, digest: Union[str, Digest]) -> str:
+        if isinstance(digest, str):
+            digest = Digest.from_string(digest)
+        return f"https://{self.domain}/v2/{self.name}/blobs/{digest}"
+
+    def with_digest(self, digest: Union[str, Digest]) -> "ImageReference":
+        if isinstance(digest, str):
+            digest = Digest.from_string(digest)
+        return ImageReference(domain=self.domain, name=self.name, tag=self.tag, digest=digest)
+
+    def with_tag(self, tag: str) -> "ImageReference":
+        return ImageReference(domain=self.domain, name=self.name, tag=tag, digest=self.digest)
+
+    def uploads_url(self, digest: Optional[Digest] = None) -> str:
+        url = f"https://{self.domain}/v2/{self.name}/blobs/uploads/"
+        if digest:
+            url += f"?digest={digest}"
+        return url
+
+    def tags_url(self) -> str:
+        return f"https://{self.domain}/v2/{self.name}/tags/list"
+
+    def endpoint(self, path: str = "") -> str:
+        return urllib.parse.urljoin(f"https://{self.domain}/v2/", path)
+
+    def __str__(self) -> str:
+        s = f"{self.domain}/{self.name}"
+        if self.tag:
+            s += f":{self.tag}"
+        if self.digest:
+            s += f"@{self.digest}"
+        return s
+
+    def __eq__(self, __value: object) -> bool:
+        if not isinstance(__value, ImageReference):
+            return NotImplemented
+        return (
+            self.domain == __value.domain
+            and self.name == __value.name
+            and self.tag == __value.tag
+            and self.digest == __value.digest
+        )
+
+
+def _ensure_valid_tag(tag: str) -> str:
+    """Ensure a tag is valid for an OCI registry."""
+    sanitized = re.sub(r"[^\w.-]", "_", tag)
+    if len(sanitized) > 128:
+        return sanitized[:64] + sanitized[-64:]
+    return sanitized
+
+
+def default_tag(spec: "spack.spec.Spec") -> str:
+    """Return a valid, default image tag for a spec."""
+    return _ensure_valid_tag(f"{spec.name}-{spec.version}-{spec.dag_hash()}.spack")
+
+
+#: Default OCI index tag
+default_index_tag = "index.spack"
+
+
+def tag_is_spec(tag: str) -> bool:
+    """Check if a tag is likely a Spec"""
+    return tag.endswith(".spack") and tag != default_index_tag
+
+
+def default_config(architecture: str, os: str):
+    return {
+        "architecture": architecture,
+        "os": os,
+        "rootfs": {"type": "layers", "diff_ids": []},
+        "config": {"Env": []},
+    }
+
+
+def default_manifest():
+    return {
+        "mediaType": "application/vnd.oci.image.manifest.v1+json",
+        "schemaVersion": 2,
+        "config": {"mediaType": "application/vnd.oci.image.config.v1+json"},
+        "layers": [],
+    }

lib/spack/spack/oci/oci.py

@@ -0,0 +1,381 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import hashlib
+import json
+import os
+import time
+import urllib.error
+import urllib.parse
+import urllib.request
+from http.client import HTTPResponse
+from typing import NamedTuple, Tuple
+from urllib.request import Request
+
+import llnl.util.tty as tty
+
+import spack.binary_distribution
+import spack.config
+import spack.error
+import spack.fetch_strategy
+import spack.mirror
+import spack.oci.opener
+import spack.repo
+import spack.spec
+import spack.stage
+import spack.traverse
+import spack.util.crypto
+
+from .image import Digest, ImageReference
+
+
+class Blob(NamedTuple):
+    compressed_digest: Digest
+    uncompressed_digest: Digest
+    size: int
+
+
+def create_tarball(spec: spack.spec.Spec, tarfile_path):
+    buildinfo = spack.binary_distribution.get_buildinfo_dict(spec)
+    return spack.binary_distribution._do_create_tarball(tarfile_path, spec.prefix, buildinfo)
+
+
+def _log_upload_progress(digest: Digest, size: int, elapsed: float):
+    elapsed = max(elapsed, 0.001)  # guard against division by zero
+    tty.info(f"Uploaded {digest} ({elapsed:.2f}s, {size / elapsed / 1024 / 1024:.2f} MB/s)")
+
+
+def with_query_param(url: str, param: str, value: str) -> str:
+    """Add a query parameter to a URL
+
+    Args:
+        url: The URL to add the parameter to.
+        param: The parameter name.
+        value: The parameter value.
+
+    Returns:
+        The URL with the parameter added.
+    """
+    parsed = urllib.parse.urlparse(url)
+    query = urllib.parse.parse_qs(parsed.query)
+    if param in query:
+        query[param].append(value)
+    else:
+        query[param] = [value]
+    return urllib.parse.urlunparse(
+        parsed._replace(query=urllib.parse.urlencode(query, doseq=True))
+    )
+
+
+def upload_blob(
+    ref: ImageReference,
+    file: str,
+    digest: Digest,
+    force: bool = False,
+    small_file_size: int = 0,
+    _urlopen: spack.oci.opener.MaybeOpen = None,
+) -> bool:
+    """Uploads a blob to an OCI registry
+
+    We only do monolithic uploads, even though it's very simple to do chunked.
+    Observed problems with chunked uploads:
+    (1) it's slow, many sequential requests, (2) some registries set an *unknown*
+    max chunk size, and the spec doesn't say how to obtain it
+
+    Args:
+        ref: The image reference.
+        file: The file to upload.
+        digest: The digest of the file.
+        force: Whether to force upload the blob, even if it already exists.
+        small_file_size: For files at most this size, attempt
+            to do a single POST request instead of POST + PUT.
+            Some registries do no support single requests, and others
+            do not specify what size they support in single POST.
+            For now this feature is disabled by default (0KB)
+
+    Returns:
+        True if the blob was uploaded, False if it already existed.
+    """
+    _urlopen = _urlopen or spack.oci.opener.urlopen
+
+    # Test if the blob already exists, if so, early exit.
+    if not force and blob_exists(ref, digest, _urlopen):
+        return False
+
+    start = time.time()
+
+    with open(file, "rb") as f:
+        file_size = os.fstat(f.fileno()).st_size
+
+        # For small blobs, do a single POST request.
+        # The spec says that registries MAY support this
+        if file_size <= small_file_size:
+            request = Request(
+                url=ref.uploads_url(digest),
+                method="POST",
+                data=f,
+                headers={
+                    "Content-Type": "application/octet-stream",
+                    "Content-Length": str(file_size),
+                },
+            )
+        else:
+            request = Request(
+                url=ref.uploads_url(), method="POST", headers={"Content-Length": "0"}
+            )
+
+        response = _urlopen(request)
+
+        # Created the blob in one go.
+        if response.status == 201:
+            _log_upload_progress(digest, file_size, time.time() - start)
+            return True
+
+        # Otherwise, do another PUT request.
+        spack.oci.opener.ensure_status(response, 202)
+        assert "Location" in response.headers
+
+        # Can be absolute or relative, joining handles both
+        upload_url = with_query_param(
+            ref.endpoint(response.headers["Location"]), "digest", str(digest)
+        )
+        f.seek(0)
+
+        response = _urlopen(
+            Request(
+                url=upload_url,
+                method="PUT",
+                data=f,
+                headers={
+                    "Content-Type": "application/octet-stream",
+                    "Content-Length": str(file_size),
+                },
+            )
+        )
+
+        spack.oci.opener.ensure_status(response, 201)
+
+    # print elapsed time and # MB/s
+    _log_upload_progress(digest, file_size, time.time() - start)
+    return True
+
+
+def upload_manifest(
+    ref: ImageReference,
+    oci_manifest: dict,
+    tag: bool = True,
+    _urlopen: spack.oci.opener.MaybeOpen = None,
+):
+    """Uploads a manifest/index to a registry
+
+    Args:
+        ref: The image reference.
+        oci_manifest: The OCI manifest or index.
+        tag: When true, use the tag, otherwise use the digest,
+            this is relevant for multi-arch images, where the
+            tag is an index, referencing the manifests by digest.
+
+    Returns:
+        The digest and size of the uploaded manifest.
+    """
+    _urlopen = _urlopen or spack.oci.opener.urlopen
+
+    data = json.dumps(oci_manifest, separators=(",", ":")).encode()
+    digest = Digest.from_sha256(hashlib.sha256(data).hexdigest())
+    size = len(data)
+
+    if not tag:
+        ref = ref.with_digest(digest)
+
+    response = _urlopen(
+        Request(
+            url=ref.manifest_url(),
+            method="PUT",
+            data=data,
+            headers={"Content-Type": oci_manifest["mediaType"]},
+        )
+    )
+
+    spack.oci.opener.ensure_status(response, 201)
+    return digest, size
+
+
+def image_from_mirror(mirror: spack.mirror.Mirror) -> ImageReference:
+    """Given an OCI based mirror, extract the URL and image name from it"""
+    url = mirror.push_url
+    if not url.startswith("oci://"):
+        raise ValueError(f"Mirror {mirror} is not an OCI mirror")
+    return ImageReference.from_string(url[6:])
+
+
+def blob_exists(
+    ref: ImageReference, digest: Digest, _urlopen: spack.oci.opener.MaybeOpen = None
+) -> bool:
+    """Checks if a blob exists in an OCI registry"""
+    try:
+        _urlopen = _urlopen or spack.oci.opener.urlopen
+        response = _urlopen(Request(url=ref.blob_url(digest), method="HEAD"))
+        return response.status == 200
+    except urllib.error.HTTPError as e:
+        if e.getcode() == 404:
+            return False
+        raise
+
+
+def copy_missing_layers(
+    src: ImageReference,
+    dst: ImageReference,
+    architecture: str,
+    _urlopen: spack.oci.opener.MaybeOpen = None,
+) -> Tuple[dict, dict]:
+    """Copy image layers from src to dst for given architecture.
+
+    Args:
+        src: The source image reference.
+        dst: The destination image reference.
+        architecture: The architecture (when referencing an index)
+
+    Returns:
+        Tuple of manifest and config of the base image.
+    """
+    _urlopen = _urlopen or spack.oci.opener.urlopen
+    manifest, config = get_manifest_and_config(src, architecture, _urlopen=_urlopen)
+
+    # Get layer digests
+    digests = [Digest.from_string(layer["digest"]) for layer in manifest["layers"]]
+
+    # Filter digests that are don't exist in the registry
+    missing_digests = [
+        digest for digest in digests if not blob_exists(dst, digest, _urlopen=_urlopen)
+    ]
+
+    if not missing_digests:
+        return manifest, config
+
+    # Pull missing blobs, push them to the registry
+    with spack.stage.StageComposite.from_iterable(
+        make_stage(url=src.blob_url(digest), digest=digest, _urlopen=_urlopen)
+        for digest in missing_digests
+    ) as stages:
+        stages.fetch()
+        stages.check()
+        stages.cache_local()
+
+        for stage, digest in zip(stages, missing_digests):
+            # No need to check existince again, force=True.
+            upload_blob(
+                dst, file=stage.save_filename, force=True, digest=digest, _urlopen=_urlopen
+            )
+
+    return manifest, config
+
+
+#: OCI manifest content types (including docker type)
+manifest_content_type = [
+    "application/vnd.oci.image.manifest.v1+json",
+    "application/vnd.docker.distribution.manifest.v2+json",
+]
+
+#: OCI index content types (including docker type)
+index_content_type = [
+    "application/vnd.oci.image.index.v1+json",
+    "application/vnd.docker.distribution.manifest.list.v2+json",
+]
+
+#: All OCI manifest / index content types
+all_content_type = manifest_content_type + index_content_type
+
+
+def get_manifest_and_config(
+    ref: ImageReference,
+    architecture="amd64",
+    recurse=3,
+    _urlopen: spack.oci.opener.MaybeOpen = None,
+) -> Tuple[dict, dict]:
+    """Recursively fetch manifest and config for a given image reference
+    with a given architecture.
+
+    Args:
+        ref: The image reference.
+        architecture: The architecture (when referencing an index)
+        recurse: How many levels of index to recurse into.
+
+    Returns:
+        A tuple of (manifest, config)"""
+
+    _urlopen = _urlopen or spack.oci.opener.urlopen
+
+    # Get manifest
+    response: HTTPResponse = _urlopen(
+        Request(url=ref.manifest_url(), headers={"Accept": ", ".join(all_content_type)})
+    )
+
+    # Recurse when we find an index
+    if response.headers["Content-Type"] in index_content_type:
+        if recurse == 0:
+            raise Exception("Maximum recursion depth reached while fetching OCI manifest")
+
+        index = json.load(response)
+        manifest_meta = next(
+            manifest
+            for manifest in index["manifests"]
+            if manifest["platform"]["architecture"] == architecture
+        )
+
+        return get_manifest_and_config(
+            ref.with_digest(manifest_meta["digest"]),
+            architecture=architecture,
+            recurse=recurse - 1,
+            _urlopen=_urlopen,
+        )
+
+    # Otherwise, require a manifest
+    if response.headers["Content-Type"] not in manifest_content_type:
+        raise Exception(f"Unknown content type {response.headers['Content-Type']}")
+
+    manifest = json.load(response)
+
+    # Download, verify and cache config file
+    config_digest = Digest.from_string(manifest["config"]["digest"])
+    with make_stage(ref.blob_url(config_digest), config_digest, _urlopen=_urlopen) as stage:
+        stage.fetch()
+        stage.check()
+        stage.cache_local()
+        with open(stage.save_filename, "rb") as f:
+            config = json.load(f)
+
+    return manifest, config
+
+
+#: Same as upload_manifest, but with retry wrapper
+upload_manifest_with_retry = spack.oci.opener.default_retry(upload_manifest)
+
+#: Same as upload_blob, but with retry wrapper
+upload_blob_with_retry = spack.oci.opener.default_retry(upload_blob)
+
+#: Same as get_manifest_and_config, but with retry wrapper
+get_manifest_and_config_with_retry = spack.oci.opener.default_retry(get_manifest_and_config)
+
+#: Same as copy_missing_layers, but with retry wrapper
+copy_missing_layers_with_retry = spack.oci.opener.default_retry(copy_missing_layers)
+
+
+def make_stage(
+    url: str, digest: Digest, keep: bool = False, _urlopen: spack.oci.opener.MaybeOpen = None
+) -> spack.stage.Stage:
+    _urlopen = _urlopen or spack.oci.opener.urlopen
+    fetch_strategy = spack.fetch_strategy.OCIRegistryFetchStrategy(
+        url, checksum=digest.digest, _urlopen=_urlopen
+    )
+    # Use blobs/<alg>/<encoded> as the cache path, which follows
+    # the OCI Image Layout Specification. What's missing though,
+    # is the `oci-layout` and `index.json` files, which are
+    # required by the spec.
+    return spack.stage.Stage(
+        fetch_strategy,
+        mirror_paths=spack.mirror.OCIImageLayout(digest),
+        name=digest.digest,
+        keep=keep,
+    )

lib/spack/spack/oci/opener.py

@@ -0,0 +1,442 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+"""All the logic for OCI fetching and authentication"""
+
+import base64
+import json
+import re
+import time
+import urllib.error
+import urllib.parse
+import urllib.request
+from enum import Enum, auto
+from http.client import HTTPResponse
+from typing import Callable, Dict, Iterable, List, NamedTuple, Optional, Tuple
+from urllib.request import Request
+
+import llnl.util.lang
+
+import spack.config
+import spack.mirror
+import spack.parser
+import spack.repo
+import spack.util.web
+
+from .image import ImageReference
+
+
+def _urlopen():
+    opener = create_opener()
+
+    def dispatch_open(fullurl, data=None, timeout=None):
+        timeout = timeout or spack.config.get("config:connect_timeout", 10)
+        return opener.open(fullurl, data, timeout)
+
+    return dispatch_open
+
+
+OpenType = Callable[..., HTTPResponse]
+MaybeOpen = Optional[OpenType]
+
+#: Opener that automatically uses OCI authentication based on mirror config
+urlopen: OpenType = llnl.util.lang.Singleton(_urlopen)
+
+
+SP = r" "
+OWS = r"[ \t]*"
+BWS = OWS
+HTAB = r"\t"
+VCHAR = r"\x21-\x7E"
+tchar = r"[!#$%&'*+\-.^_`|~0-9A-Za-z]"
+token = rf"{tchar}+"
+obs_text = r"\x80-\xFF"
+qdtext = rf"[{HTAB}{SP}\x21\x23-\x5B\x5D-\x7E{obs_text}]"
+quoted_pair = rf"\\([{HTAB}{SP}{VCHAR}{obs_text}])"
+quoted_string = rf'"(?:({qdtext}*)|{quoted_pair})*"'
+
+
+class TokenType(spack.parser.TokenBase):
+    AUTH_PARAM = rf"({token}){BWS}={BWS}({token}|{quoted_string})"
+    # TOKEN68 = r"([A-Za-z0-9\-._~+/]+=*)"  # todo... support this?
+    TOKEN = rf"{tchar}+"
+    EQUALS = rf"{BWS}={BWS}"
+    COMMA = rf"{OWS},{OWS}"
+    SPACE = r" +"
+    EOF = r"$"
+    ANY = r"."
+
+
+TOKEN_REGEXES = [rf"(?P<{token}>{token.regex})" for token in TokenType]
+
+ALL_TOKENS = re.compile("|".join(TOKEN_REGEXES))
+
+
+class State(Enum):
+    CHALLENGE = auto()
+    AUTH_PARAM_LIST_START = auto()
+    AUTH_PARAM = auto()
+    NEXT_IN_LIST = auto()
+    AUTH_PARAM_OR_SCHEME = auto()
+
+
+def tokenize(input: str):
+    scanner = ALL_TOKENS.scanner(input)  # type: ignore[attr-defined]
+
+    for match in iter(scanner.match, None):  # type: ignore[var-annotated]
+        yield spack.parser.Token(
+            TokenType.__members__[match.lastgroup],  # type: ignore[attr-defined]
+            match.group(),  # type: ignore[attr-defined]
+            match.start(),  # type: ignore[attr-defined]
+            match.end(),  # type: ignore[attr-defined]
+        )
+
+
+class Challenge:
+    __slots__ = ["scheme", "params"]
+
+    def __init__(
+        self, scheme: Optional[str] = None, params: Optional[List[Tuple[str, str]]] = None
+    ) -> None:
+        self.scheme = scheme or ""
+        self.params = params or []
+
+    def __repr__(self) -> str:
+        return f"Challenge({self.scheme}, {self.params})"
+
+    def __eq__(self, other: object) -> bool:
+        return (
+            isinstance(other, Challenge)
+            and self.scheme == other.scheme
+            and self.params == other.params
+        )
+
+
+def parse_www_authenticate(input: str):
+    """Very basic parsing of www-authenticate parsing (RFC7235 section 4.1)
+    Notice: this omits token68 support."""
+
+    # auth-scheme      = token
+    # auth-param       = token BWS "=" BWS ( token / quoted-string )
+    # challenge        = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
+    # WWW-Authenticate = 1#challenge
+
+    challenges: List[Challenge] = []
+
+    _unquote = re.compile(quoted_pair).sub
+    unquote = lambda s: _unquote(r"\1", s[1:-1])
+
+    mode: State = State.CHALLENGE
+    tokens = tokenize(input)
+
+    current_challenge = Challenge()
+
+    def extract_auth_param(input: str) -> Tuple[str, str]:
+        key, value = input.split("=", 1)
+        key = key.rstrip()
+        value = value.lstrip()
+        if value.startswith('"'):
+            value = unquote(value)
+        return key, value
+
+    while True:
+        token: spack.parser.Token = next(tokens)
+
+        if mode == State.CHALLENGE:
+            if token.kind == TokenType.EOF:
+                raise ValueError(token)
+            elif token.kind == TokenType.TOKEN:
+                current_challenge.scheme = token.value
+                mode = State.AUTH_PARAM_LIST_START
+            else:
+                raise ValueError(token)
+
+        elif mode == State.AUTH_PARAM_LIST_START:
+            if token.kind == TokenType.EOF:
+                challenges.append(current_challenge)
+                break
+            elif token.kind == TokenType.COMMA:
+                # Challenge without param list, followed by another challenge.
+                challenges.append(current_challenge)
+                current_challenge = Challenge()
+                mode = State.CHALLENGE
+            elif token.kind == TokenType.SPACE:
+                # A space means it must be followed by param list
+                mode = State.AUTH_PARAM
+            else:
+                raise ValueError(token)
+
+        elif mode == State.AUTH_PARAM:
+            if token.kind == TokenType.EOF:
+                raise ValueError(token)
+            elif token.kind == TokenType.AUTH_PARAM:
+                key, value = extract_auth_param(token.value)
+                current_challenge.params.append((key, value))
+                mode = State.NEXT_IN_LIST
+            else:
+                raise ValueError(token)
+
+        elif mode == State.NEXT_IN_LIST:
+            if token.kind == TokenType.EOF:
+                challenges.append(current_challenge)
+                break
+            elif token.kind == TokenType.COMMA:
+                mode = State.AUTH_PARAM_OR_SCHEME
+            else:
+                raise ValueError(token)
+
+        elif mode == State.AUTH_PARAM_OR_SCHEME:
+            if token.kind == TokenType.EOF:
+                raise ValueError(token)
+            elif token.kind == TokenType.TOKEN:
+                challenges.append(current_challenge)
+                current_challenge = Challenge(token.value)
+                mode = State.AUTH_PARAM_LIST_START
+            elif token.kind == TokenType.AUTH_PARAM:
+                key, value = extract_auth_param(token.value)
+                current_challenge.params.append((key, value))
+                mode = State.NEXT_IN_LIST
+
+    return challenges
+
+
+class RealmServiceScope(NamedTuple):
+    realm: str
+    service: str
+    scope: str
+
+
+class UsernamePassword(NamedTuple):
+    username: str
+    password: str
+
+
+def get_bearer_challenge(challenges: List[Challenge]) -> Optional[RealmServiceScope]:
+    # Find a challenge that we can handle (currently only Bearer)
+    challenge = next((c for c in challenges if c.scheme == "Bearer"), None)
+
+    if challenge is None:
+        return None
+
+    # Get realm / service / scope from challenge
+    realm = next((v for k, v in challenge.params if k == "realm"), None)
+    service = next((v for k, v in challenge.params if k == "service"), None)
+    scope = next((v for k, v in challenge.params if k == "scope"), None)
+
+    if realm is None or service is None or scope is None:
+        return None
+
+    return RealmServiceScope(realm, service, scope)
+
+
+class OCIAuthHandler(urllib.request.BaseHandler):
+    def __init__(self, credentials_provider: Callable[[str], Optional[UsernamePassword]]):
+        """
+        Args:
+            credentials_provider: A function that takes a domain and may return a UsernamePassword.
+        """
+        self.credentials_provider = credentials_provider
+
+        # Cached bearer tokens for a given domain.
+        self.cached_tokens: Dict[str, str] = {}
+
+    def obtain_bearer_token(self, registry: str, challenge: RealmServiceScope, timeout) -> str:
+        # See https://docs.docker.com/registry/spec/auth/token/
+
+        query = urllib.parse.urlencode(
+            {"service": challenge.service, "scope": challenge.scope, "client_id": "spack"}
+        )
+
+        parsed = urllib.parse.urlparse(challenge.realm)._replace(
+            query=query, fragment="", params=""
+        )
+
+        # Don't send credentials over insecure transport.
+        if parsed.scheme != "https":
+            raise ValueError(
+                f"Cannot login to {registry} over insecure {parsed.scheme} connection"
+            )
+
+        request = Request(urllib.parse.urlunparse(parsed))
+
+        # I guess we shouldn't cache this, since we don't know
+        # the context in which it's used (may depend on config)
+        pair = self.credentials_provider(registry)
+
+        if pair is not None:
+            encoded = base64.b64encode(f"{pair.username}:{pair.password}".encode("utf-8")).decode(
+                "utf-8"
+            )
+            request.add_unredirected_header("Authorization", f"Basic {encoded}")
+
+        # Do a GET request.
+        response = self.parent.open(request, timeout=timeout)
+
+        # Read the response and parse the JSON
+        response_json = json.load(response)
+
+        # Get the token from the response
+        token = response_json["token"]
+
+        # Remember the last obtained token for this registry
+        # Note: we should probably take into account realm, service and scope
+        # so we can store multiple tokens for the same registry.
+        self.cached_tokens[registry] = token
+
+        return token
+
+    def https_request(self, req: Request):
+        # Eagerly add the bearer token to the request if no
+        # auth header is set yet, to avoid 401s in multiple
+        # requests to the same registry.
+
+        # Use has_header, not .headers, since there are two
+        # types of headers (redirected and unredirected)
+        if req.has_header("Authorization"):
+            return req
+
+        parsed = urllib.parse.urlparse(req.full_url)
+        token = self.cached_tokens.get(parsed.netloc)
+
+        if not token:
+            return req
+
+        req.add_unredirected_header("Authorization", f"Bearer {token}")
+        return req
+
+    def http_error_401(self, req: Request, fp, code, msg, headers):
+        # Login failed, avoid infinite recursion where we go back and
+        # forth between auth server and registry
+        if hasattr(req, "login_attempted"):
+            raise urllib.error.HTTPError(
+                req.full_url, code, f"Failed to login to {req.full_url}: {msg}", headers, fp
+            )
+
+        # On 401 Unauthorized, parse the WWW-Authenticate header
+        # to determine what authentication is required
+        if "WWW-Authenticate" not in headers:
+            raise urllib.error.HTTPError(
+                req.full_url,
+                code,
+                "Cannot login to registry, missing WWW-Authenticate header",
+                headers,
+                fp,
+            )
+
+        header_value = headers["WWW-Authenticate"]
+
+        try:
+            challenge = get_bearer_challenge(parse_www_authenticate(header_value))
+        except ValueError as e:
+            raise urllib.error.HTTPError(
+                req.full_url,
+                code,
+                f"Cannot login to registry, malformed WWW-Authenticate header: {header_value}",
+                headers,
+                fp,
+            ) from e
+
+        # If there is no bearer challenge, we can't handle it
+        if not challenge:
+            raise urllib.error.HTTPError(
+                req.full_url,
+                code,
+                f"Cannot login to registry, unsupported authentication scheme: {header_value}",
+                headers,
+                fp,
+            )
+
+        # Get the token from the auth handler
+        try:
+            token = self.obtain_bearer_token(
+                registry=urllib.parse.urlparse(req.get_full_url()).netloc,
+                challenge=challenge,
+                timeout=req.timeout,
+            )
+        except ValueError as e:
+            raise urllib.error.HTTPError(
+                req.full_url,
+                code,
+                f"Cannot login to registry, failed to obtain bearer token: {e}",
+                headers,
+                fp,
+            ) from e
+
+        # Add the token to the request
+        req.add_unredirected_header("Authorization", f"Bearer {token}")
+        setattr(req, "login_attempted", True)
+
+        return self.parent.open(req, timeout=req.timeout)
+
+
+def credentials_from_mirrors(
+    domain: str, *, mirrors: Optional[Iterable[spack.mirror.Mirror]] = None
+) -> Optional[UsernamePassword]:
+    """Filter out OCI registry credentials from a list of mirrors."""
+
+    mirrors = mirrors or spack.mirror.MirrorCollection().values()
+
+    for mirror in mirrors:
+        # Prefer push credentials over fetch. Unlikely that those are different
+        # but our config format allows it.
+        for direction in ("push", "fetch"):
+            pair = mirror.get_access_pair(direction)
+            if pair is None:
+                continue
+            url = mirror.get_url(direction)
+            if not url.startswith("oci://"):
+                continue
+            try:
+                parsed = ImageReference.from_string(url[6:])
+            except ValueError:
+                continue
+            if parsed.domain == domain:
+                return UsernamePassword(*pair)
+    return None
+
+
+def create_opener():
+    """Create an opener that can handle OCI authentication."""
+    opener = urllib.request.OpenerDirector()
+    for handler in [
+        urllib.request.UnknownHandler(),
+        urllib.request.HTTPSHandler(),
+        spack.util.web.SpackHTTPDefaultErrorHandler(),
+        urllib.request.HTTPRedirectHandler(),
+        urllib.request.HTTPErrorProcessor(),
+        OCIAuthHandler(credentials_from_mirrors),
+    ]:
+        opener.add_handler(handler)
+    return opener
+
+
+def ensure_status(response: HTTPResponse, status: int):
+    """Raise an error if the response status is not the expected one."""
+    if response.status == status:
+        return
+
+    raise urllib.error.HTTPError(
+        response.geturl(), response.status, response.reason, response.info(), None
+    )
+
+
+def default_retry(f, retries: int = 3, sleep=None):
+    sleep = sleep or time.sleep
+
+    def wrapper(*args, **kwargs):
+        for i in range(retries):
+            try:
+                return f(*args, **kwargs)
+            except urllib.error.HTTPError as e:
+                # Retry on internal server errors, and rate limit errors
+                # Potentially this could take into account the Retry-After header
+                # if registries support it
+                if i + 1 != retries and (500 <= e.code < 600 or e.code == 429):
+                    # Exponential backoff
+                    sleep(2**i)
+                    continue
+                raise
+
+    return wrapper

lib/spack/spack/operating_systems/windows_os.py

@@ -5,10 +5,12 @@
 
 import glob
 import os
+import pathlib
 import platform
 import subprocess
 
 from spack.error import SpackError
+from spack.util import windows_registry as winreg
 from spack.version import Version
 
 from ._operating_system import OperatingSystem
@@ -31,43 +33,6 @@ class WindowsOs(OperatingSystem):
     10.
     """
 
-    # Find MSVC directories using vswhere
-    comp_search_paths = []
-    vs_install_paths = []
-    root = os.environ.get("ProgramFiles(x86)") or os.environ.get("ProgramFiles")
-    if root:
-        try:
-            extra_args = {"encoding": "mbcs", "errors": "strict"}
-            paths = subprocess.check_output(  # type: ignore[call-overload] # novermin
-                [
-                    os.path.join(root, "Microsoft Visual Studio", "Installer", "vswhere.exe"),
-                    "-prerelease",
-                    "-requires",
-                    "Microsoft.VisualStudio.Component.VC.Tools.x86.x64",
-                    "-property",
-                    "installationPath",
-                    "-products",
-                    "*",
-                ],
-                **extra_args,
-            ).strip()
-            vs_install_paths = paths.split("\n")
-            msvc_paths = [os.path.join(path, "VC", "Tools", "MSVC") for path in vs_install_paths]
-            for p in msvc_paths:
-                comp_search_paths.extend(glob.glob(os.path.join(p, "*", "bin", "Hostx64", "x64")))
-            if os.getenv("ONEAPI_ROOT"):
-                comp_search_paths.extend(
-                    glob.glob(
-                        os.path.join(
-                            str(os.getenv("ONEAPI_ROOT")), "compiler", "*", "windows", "bin"
-                        )
-                    )
-                )
-        except (subprocess.CalledProcessError, OSError, UnicodeDecodeError):
-            pass
-    if comp_search_paths:
-        compiler_search_paths = comp_search_paths
-
     def __init__(self):
         plat_ver = windows_version()
         if plat_ver < Version("10"):
@@ -76,3 +41,71 @@ def __init__(self):
 
     def __str__(self):
         return self.name
+
+    @property
+    def vs_install_paths(self):
+        vs_install_paths = []
+        root = os.environ.get("ProgramFiles(x86)") or os.environ.get("ProgramFiles")
+        if root:
+            try:
+                extra_args = {"encoding": "mbcs", "errors": "strict"}
+                paths = subprocess.check_output(  # type: ignore[call-overload] # novermin
+                    [
+                        os.path.join(root, "Microsoft Visual Studio", "Installer", "vswhere.exe"),
+                        "-prerelease",
+                        "-requires",
+                        "Microsoft.VisualStudio.Component.VC.Tools.x86.x64",
+                        "-property",
+                        "installationPath",
+                        "-products",
+                        "*",
+                    ],
+                    **extra_args,
+                ).strip()
+                vs_install_paths = paths.split("\n")
+            except (subprocess.CalledProcessError, OSError, UnicodeDecodeError):
+                pass
+        return vs_install_paths
+
+    @property
+    def msvc_paths(self):
+        return [os.path.join(path, "VC", "Tools", "MSVC") for path in self.vs_install_paths]
+
+    @property
+    def compiler_search_paths(self):
+        # First Strategy: Find MSVC directories using vswhere
+        _compiler_search_paths = []
+        for p in self.msvc_paths:
+            _compiler_search_paths.extend(glob.glob(os.path.join(p, "*", "bin", "Hostx64", "x64")))
+        if os.getenv("ONEAPI_ROOT"):
+            _compiler_search_paths.extend(
+                glob.glob(
+                    os.path.join(str(os.getenv("ONEAPI_ROOT")), "compiler", "*", "windows", "bin")
+                )
+            )
+        # Second strategy: Find MSVC via the registry
+        msft = winreg.WindowsRegistryView(
+            "SOFTWARE\\WOW6432Node\\Microsoft", winreg.HKEY.HKEY_LOCAL_MACHINE
+        )
+        vs_entries = msft.find_subkeys(r"VisualStudio_.*")
+        vs_paths = []
+
+        def clean_vs_path(path):
+            path = path.split(",")[0].lstrip("@")
+            return str((pathlib.Path(path).parent / "..\\..").resolve())
+
+        for entry in vs_entries:
+            try:
+                val = entry.get_subkey("Capabilities").get_value("ApplicationDescription").value
+                vs_paths.append(clean_vs_path(val))
+            except FileNotFoundError as e:
+                if hasattr(e, "winerror"):
+                    if e.winerror == 2:
+                        pass
+                    else:
+                        raise
+                else:
+                    raise
+
+        _compiler_search_paths.extend(vs_paths)
+        return _compiler_search_paths

lib/spack/spack/package.py

@@ -49,6 +49,7 @@
 from spack.build_systems.nmake import NMakePackage
 from spack.build_systems.octave import OctavePackage
 from spack.build_systems.oneapi import (
+    INTEL_MATH_LIBRARIES,
     IntelOneApiLibraryPackage,
     IntelOneApiPackage,
     IntelOneApiStaticLibraryList,
@@ -85,7 +86,7 @@
     UpstreamPackageError,
 )
 from spack.mixins import filter_compiler_wrappers
-from spack.multimethod import when
+from spack.multimethod import default_args, when
 from spack.package_base import (
     DependencyConflictError,
     build_system_flags,

lib/spack/spack/parser.py

@@ -6,7 +6,7 @@
 
 Here is the EBNF grammar for a spec::
 
-    spec          = [name] [node_options] { ^ node } |
+    spec          = [name] [node_options] { ^[edge_properties] node } |
                     [name] [node_options] hash |
                     filename
 
@@ -14,7 +14,8 @@
                      [name] [node_options] hash |
                      filename
 
-    node_options  = [@(version_list|version_pair)] [%compiler] { variant }
+    node_options    = [@(version_list|version_pair)] [%compiler] { variant }
+    edge_properties = [ { bool_variant | key_value } ]
 
     hash          = / id
     filename      = (.|/|[a-zA-Z0-9-_]*/)([a-zA-Z0-9-_./]*)(.json|.yaml)
@@ -64,9 +65,9 @@
 
 from llnl.util.tty import color
 
+import spack.deptypes
 import spack.error
 import spack.spec
-import spack.variant
 import spack.version
 
 IS_WINDOWS = sys.platform == "win32"
@@ -97,9 +98,9 @@
 VALUE = r"(?:[a-zA-Z_0-9\-+\*.,:=\~\/\\]+)"
 QUOTED_VALUE = r"[\"']+(?:[a-zA-Z_0-9\-+\*.,:=\~\/\\\s]+)[\"']+"
 
-VERSION = r"=?([a-zA-Z0-9_][a-zA-Z_0-9\-\.]*\b)"
-VERSION_RANGE = rf"({VERSION}\s*:\s*{VERSION}(?!\s*=)|:\s*{VERSION}(?!\s*=)|{VERSION}\s*:|:)"
-VERSION_LIST = rf"({VERSION_RANGE}|{VERSION})(\s*[,]\s*({VERSION_RANGE}|{VERSION}))*"
+VERSION = r"=?(?:[a-zA-Z0-9_][a-zA-Z_0-9\-\.]*\b)"
+VERSION_RANGE = rf"(?:(?:{VERSION})?:(?:{VERSION}(?!\s*=))?)"
+VERSION_LIST = rf"(?:{VERSION_RANGE}|{VERSION})(?:\s*,\s*(?:{VERSION_RANGE}|{VERSION}))*"
 
 
 class TokenBase(enum.Enum):
@@ -127,6 +128,8 @@ class TokenType(TokenBase):
     """
 
     # Dependency
+    START_EDGE_PROPERTIES = r"(?:\^\[)"
+    END_EDGE_PROPERTIES = r"(?:\])"
     DEPENDENCY = r"(?:\^)"
     # Version
     VERSION_HASH_PAIR = rf"(?:@(?:{GIT_VERSION_PATTERN})=(?:{VERSION}))"
@@ -164,7 +167,7 @@ class Token:
     __slots__ = "kind", "value", "start", "end"
 
     def __init__(
-        self, kind: TokenType, value: str, start: Optional[int] = None, end: Optional[int] = None
+        self, kind: TokenBase, value: str, start: Optional[int] = None, end: Optional[int] = None
     ):
         self.kind = kind
         self.value = value
@@ -264,8 +267,8 @@ def tokens(self) -> List[Token]:
         return list(filter(lambda x: x.kind != TokenType.WS, tokenize(self.literal_str)))
 
     def next_spec(
-        self, initial_spec: Optional[spack.spec.Spec] = None
-    ) -> Optional[spack.spec.Spec]:
+        self, initial_spec: Optional["spack.spec.Spec"] = None
+    ) -> Optional["spack.spec.Spec"]:
         """Return the next spec parsed from text.
 
         Args:
@@ -281,16 +284,15 @@ def next_spec(
         initial_spec = initial_spec or spack.spec.Spec()
         root_spec = SpecNodeParser(self.ctx).parse(initial_spec)
         while True:
-            if self.ctx.accept(TokenType.DEPENDENCY):
-                dependency = SpecNodeParser(self.ctx).parse()
-
-                if dependency is None:
-                    msg = (
-                        "this dependency sigil needs to be followed by a package name "
-                        "or a node attribute (version, variant, etc.)"
-                    )
-                    raise SpecParsingError(msg, self.ctx.current_token, self.literal_str)
+            if self.ctx.accept(TokenType.START_EDGE_PROPERTIES):
+                edge_properties = EdgeAttributeParser(self.ctx, self.literal_str).parse()
+                edge_properties.setdefault("depflag", 0)
+                edge_properties.setdefault("virtuals", ())
+                dependency = self._parse_node(root_spec)
+                root_spec._add_dependency(dependency, **edge_properties)
 
+            elif self.ctx.accept(TokenType.DEPENDENCY):
+                dependency = self._parse_node(root_spec)
                 root_spec._add_dependency(dependency, depflag=0, virtuals=())
 
             else:
@@ -298,7 +300,19 @@ def next_spec(
 
         return root_spec
 
-    def all_specs(self) -> List[spack.spec.Spec]:
+    def _parse_node(self, root_spec):
+        dependency = SpecNodeParser(self.ctx).parse()
+        if dependency is None:
+            msg = (
+                "the dependency sigil and any optional edge attributes must be followed by a "
+                "package name or a node attribute (version, variant, etc.)"
+            )
+            raise SpecParsingError(msg, self.ctx.current_token, self.literal_str)
+        if root_spec.concrete:
+            raise spack.spec.RedundantSpecError(root_spec, "^" + str(dependency))
+        return dependency
+
+    def all_specs(self) -> List["spack.spec.Spec"]:
         """Return all the specs that remain to be parsed"""
         return list(iter(self.next_spec, None))
 
@@ -313,7 +327,9 @@ def __init__(self, ctx):
         self.has_compiler = False
         self.has_version = False
 
-    def parse(self, initial_spec: Optional[spack.spec.Spec] = None) -> Optional[spack.spec.Spec]:
+    def parse(
+        self, initial_spec: Optional["spack.spec.Spec"] = None
+    ) -> Optional["spack.spec.Spec"]:
         """Parse a single spec node from a stream of tokens
 
         Args:
@@ -414,7 +430,7 @@ class FileParser:
     def __init__(self, ctx):
         self.ctx = ctx
 
-    def parse(self, initial_spec: spack.spec.Spec) -> spack.spec.Spec:
+    def parse(self, initial_spec: "spack.spec.Spec") -> "spack.spec.Spec":
         """Parse a spec tree from a specfile.
 
         Args:
@@ -437,7 +453,42 @@ def parse(self, initial_spec: spack.spec.Spec) -> spack.spec.Spec:
         return initial_spec
 
 
-def parse(text: str) -> List[spack.spec.Spec]:
+class EdgeAttributeParser:
+    __slots__ = "ctx", "literal_str"
+
+    def __init__(self, ctx, literal_str):
+        self.ctx = ctx
+        self.literal_str = literal_str
+
+    def parse(self):
+        attributes = {}
+        while True:
+            if self.ctx.accept(TokenType.KEY_VALUE_PAIR):
+                name, value = self.ctx.current_token.value.split("=", maxsplit=1)
+                name = name.strip("'\" ")
+                value = value.strip("'\" ").split(",")
+                attributes[name] = value
+                if name not in ("deptypes", "virtuals"):
+                    msg = (
+                        "the only edge attributes that are currently accepted "
+                        'are "deptypes" and "virtuals"'
+                    )
+                    raise SpecParsingError(msg, self.ctx.current_token, self.literal_str)
+            # TODO: Add code to accept bool variants here as soon as use variants are implemented
+            elif self.ctx.accept(TokenType.END_EDGE_PROPERTIES):
+                break
+            else:
+                msg = "unexpected token in edge attributes"
+                raise SpecParsingError(msg, self.ctx.next_token, self.literal_str)
+
+        # Turn deptypes=... to depflag representation
+        if "deptypes" in attributes:
+            deptype_string = attributes.pop("deptypes")
+            attributes["depflag"] = spack.deptypes.canonicalize(deptype_string)
+        return attributes
+
+
+def parse(text: str) -> List["spack.spec.Spec"]:
     """Parse text into a list of strings
 
     Args:
@@ -450,8 +501,8 @@ def parse(text: str) -> List[spack.spec.Spec]:
 
 
 def parse_one_or_raise(
-    text: str, initial_spec: Optional[spack.spec.Spec] = None
-) -> spack.spec.Spec:
+    text: str, initial_spec: Optional["spack.spec.Spec"] = None
+) -> "spack.spec.Spec":
     """Parse exactly one spec from text and return it, or raise
 
     Args:

lib/spack/spack/patch.py

@@ -7,6 +7,7 @@
 import inspect
 import os
 import os.path
+import pathlib
 import sys
 
 import llnl.util.filesystem
@@ -36,10 +37,12 @@ def apply_patch(stage, patch_path, level=1, working_dir="."):
     """
     git_utils_path = os.environ.get("PATH", "")
     if sys.platform == "win32":
-        git = which_string("git", required=True)
-        git_root = git.split("\\")[:-2]
-        git_root.extend(["usr", "bin"])
-        git_utils_path = os.sep.join(git_root)
+        git = which_string("git")
+        if git:
+            git = pathlib.Path(git)
+            git_root = git.parent.parent
+            git_root = git_root / "usr" / "bin"
+            git_utils_path = os.pathsep.join([str(git_root), git_utils_path])
 
     # TODO: Decouple Spack's patch support on Windows from Git
     # for Windows, and instead have Spack directly fetch, install, and

lib/spack/spack/provider_index.py

@@ -3,7 +3,6 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 """Classes and functions to manage providers of virtual dependencies"""
-import itertools
 from typing import Dict, List, Optional, Set
 
 import spack.error
@@ -11,33 +10,6 @@
 import spack.util.spack_json as sjson
 
 
-def _cross_provider_maps(lmap, rmap):
-    """Return a dictionary that combines constraint requests from both input.
-
-    Args:
-        lmap: main provider map
-        rmap: provider map with additional constraints
-    """
-    # TODO: this is pretty darned nasty, and inefficient, but there
-    # TODO: are not that many vdeps in most specs.
-    result = {}
-    for lspec, rspec in itertools.product(lmap, rmap):
-        try:
-            constrained = lspec.constrained(rspec)
-        except spack.error.UnsatisfiableSpecError:
-            continue
-
-        # lp and rp are left and right provider specs.
-        for lp_spec, rp_spec in itertools.product(lmap[lspec], rmap[rspec]):
-            if lp_spec.name == rp_spec.name:
-                try:
-                    const = lp_spec.constrained(rp_spec, deps=False)
-                    result.setdefault(constrained, set()).add(const)
-                except spack.error.UnsatisfiableSpecError:
-                    continue
-    return result
-
-
 class _IndexBase:
     #: This is a dict of dicts used for finding providers of particular
     #: virtual dependencies. The dict of dicts looks like:
@@ -81,29 +53,6 @@ def providers_for(self, virtual_spec):
     def __contains__(self, name):
         return name in self.providers
 
-    def satisfies(self, other):
-        """Determine if the providers of virtual specs are compatible.
-
-        Args:
-            other: another provider index
-
-        Returns:
-            True if the providers are compatible, False otherwise.
-        """
-        common = set(self.providers) & set(other.providers)
-        if not common:
-            return True
-
-        # This ensures that some provider in other COULD satisfy the
-        # vpkg constraints on self.
-        result = {}
-        for name in common:
-            crossed = _cross_provider_maps(self.providers[name], other.providers[name])
-            if crossed:
-                result[name] = crossed
-
-        return all(c in result for c in common)
-
     def __eq__(self, other):
         return self.providers == other.providers
 

lib/spack/spack/repo.py

@@ -6,6 +6,7 @@
 import abc
 import collections.abc
 import contextlib
+import difflib
 import errno
 import functools
 import importlib
@@ -1516,7 +1517,18 @@ def __init__(self, name, repo=None):
                 long_msg = "Did you mean to specify a filename with './{0}'?"
                 long_msg = long_msg.format(name)
             else:
-                long_msg = "You may need to run 'spack clean -m'."
+                long_msg = "Use 'spack create' to create a new package."
+
+                if not repo:
+                    repo = spack.repo.PATH
+
+                # We need to compare the base package name
+                pkg_name = name.rsplit(".", 1)[-1]
+                similar = difflib.get_close_matches(pkg_name, repo.all_package_names())
+
+                if 1 <= len(similar) <= 5:
+                    long_msg += "\n\nDid you mean one of the following packages?\n  "
+                    long_msg += "\n  ".join(similar)
 
         super().__init__(msg, long_msg)
         self.name = name

lib/spack/spack/schema/__init__.py

@@ -62,3 +62,25 @@ def _deprecated_properties(validator, deprecated, instance, schema):
 
 
 Validator = llnl.util.lang.Singleton(_make_validator)
+
+spec_list_schema = {
+    "type": "array",
+    "default": [],
+    "items": {
+        "anyOf": [
+            {
+                "type": "object",
+                "additionalProperties": False,
+                "properties": {
+                    "matrix": {
+                        "type": "array",
+                        "items": {"type": "array", "items": {"type": "string"}},
+                    },
+                    "exclude": {"type": "array", "items": {"type": "string"}},
+                },
+            },
+            {"type": "string"},
+            {"type": "null"},
+        ]
+    },
+}

lib/spack/spack/schema/config.py

@@ -92,6 +92,7 @@
             "url_fetch_method": {"type": "string", "enum": ["urllib", "curl"]},
             "additional_external_search_paths": {"type": "array", "items": {"type": "string"}},
             "binary_index_ttl": {"type": "integer", "minimum": 0},
+            "aliases": {"type": "object", "patternProperties": {r"\w[\w-]*": {"type": "string"}}},
         },
         "deprecatedProperties": {
             "properties": ["terminal_title"],

lib/spack/spack/schema/definitions.py

@@ -0,0 +1,34 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+"""Schema for definitions
+
+.. literalinclude:: _spack_root/lib/spack/spack/schema/definitions.py
+   :lines: 13-
+"""
+
+import spack.schema
+
+#: Properties for inclusion in other schemas
+properties = {
+    "definitions": {
+        "type": "array",
+        "default": [],
+        "items": {
+            "type": "object",
+            "properties": {"when": {"type": "string"}},
+            "patternProperties": {r"^(?!when$)\w*": spack.schema.spec_list_schema},
+        },
+    }
+}
+
+#: Full schema with metadata
+schema = {
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "title": "Spack definitions configuration file schema",
+    "type": "object",
+    "additionalProperties": False,
+    "properties": properties,
+}

lib/spack/spack/schema/env.py

@@ -12,34 +12,11 @@
 
 import spack.schema.gitlab_ci  # DEPRECATED
 import spack.schema.merged
-import spack.schema.packages
 import spack.schema.projections
 
 #: Top level key in a manifest file
 TOP_LEVEL_KEY = "spack"
 
-spec_list_schema = {
-    "type": "array",
-    "default": [],
-    "items": {
-        "anyOf": [
-            {
-                "type": "object",
-                "additionalProperties": False,
-                "properties": {
-                    "matrix": {
-                        "type": "array",
-                        "items": {"type": "array", "items": {"type": "string"}},
-                    },
-                    "exclude": {"type": "array", "items": {"type": "string"}},
-                },
-            },
-            {"type": "string"},
-            {"type": "null"},
-        ]
-    },
-}
-
 projections_scheme = spack.schema.projections.properties["projections"]
 
 schema = {
@@ -75,16 +52,7 @@
                             }
                         },
                     },
-                    "definitions": {
-                        "type": "array",
-                        "default": [],
-                        "items": {
-                            "type": "object",
-                            "properties": {"when": {"type": "string"}},
-                            "patternProperties": {r"^(?!when$)\w*": spec_list_schema},
-                        },
-                    },
-                    "specs": spec_list_schema,
+                    "specs": spack.schema.spec_list_schema,
                     "view": {
                         "anyOf": [
                             {"type": "boolean"},

lib/spack/spack/schema/merged.py

@@ -17,6 +17,7 @@
 import spack.schema.concretizer
 import spack.schema.config
 import spack.schema.container
+import spack.schema.definitions
 import spack.schema.mirrors
 import spack.schema.modules
 import spack.schema.packages
@@ -32,6 +33,7 @@
     spack.schema.config.properties,
     spack.schema.container.properties,
     spack.schema.ci.properties,
+    spack.schema.definitions.properties,
     spack.schema.mirrors.properties,
     spack.schema.modules.properties,
     spack.schema.packages.properties,

lib/spack/spack/schema/modules.py

@@ -17,10 +17,8 @@
 #: THIS NEEDS TO BE UPDATED FOR EVERY NEW KEYWORD THAT
 #: IS ADDED IMMEDIATELY BELOW THE MODULE TYPE ATTRIBUTE
 spec_regex = (
-    r"(?!hierarchy|core_specs|verbose|hash_length|defaults|filter_hierarchy_specs|"
-    r"whitelist|blacklist|"  # DEPRECATED: remove in 0.20.
-    r"include|exclude|"  # use these more inclusive/consistent options
-    r"projections|naming_scheme|core_compilers|all)(^\w[\w-]*)"
+    r"(?!hierarchy|core_specs|verbose|hash_length|defaults|filter_hierarchy_specs|hide|"
+    r"include|exclude|projections|naming_scheme|core_compilers|all)(^\w[\w-]*)"
 )
 
 #: Matches a valid name for a module set
@@ -46,14 +44,7 @@
             "default": {},
             "additionalProperties": False,
             "properties": {
-                # DEPRECATED: remove in 0.20.
-                "environment_blacklist": {
-                    "type": "array",
-                    "default": [],
-                    "items": {"type": "string"},
-                },
-                # use exclude_env_vars instead
-                "exclude_env_vars": {"type": "array", "default": [], "items": {"type": "string"}},
+                "exclude_env_vars": {"type": "array", "default": [], "items": {"type": "string"}}
             },
         },
         "template": {"type": "string"},
@@ -80,15 +71,11 @@
             "properties": {
                 "verbose": {"type": "boolean", "default": False},
                 "hash_length": {"type": "integer", "minimum": 0, "default": 7},
-                # DEPRECATED: remove in 0.20.
-                "whitelist": array_of_strings,
-                "blacklist": array_of_strings,
-                "blacklist_implicits": {"type": "boolean", "default": False},
-                # whitelist/blacklist have been replaced with include/exclude
                 "include": array_of_strings,
                 "exclude": array_of_strings,
                 "exclude_implicits": {"type": "boolean", "default": False},
                 "defaults": array_of_strings,
+                "hide_implicits": {"type": "boolean", "default": False},
                 "naming_scheme": {"type": "string"},  # Can we be more specific here?
                 "projections": projections_scheme,
                 "all": module_file_configuration,

lib/spack/spack/schema/packages.py

@@ -8,6 +8,66 @@
    :lines: 13-
 """
 
+permissions = {
+    "type": "object",
+    "additionalProperties": False,
+    "properties": {
+        "read": {"type": "string", "enum": ["user", "group", "world"]},
+        "write": {"type": "string", "enum": ["user", "group", "world"]},
+        "group": {"type": "string"},
+    },
+}
+
+variants = {"oneOf": [{"type": "string"}, {"type": "array", "items": {"type": "string"}}]}
+
+requirements = {
+    "oneOf": [
+        # 'require' can be a list of requirement_groups.
+        # each requirement group is a list of one or more
+        # specs. Either at least one or exactly one spec
+        # in the group must be satisfied (depending on
+        # whether you use "any_of" or "one_of",
+        # repectively)
+        {
+            "type": "array",
+            "items": {
+                "oneOf": [
+                    {
+                        "type": "object",
+                        "additionalProperties": False,
+                        "properties": {
+                            "one_of": {"type": "array", "items": {"type": "string"}},
+                            "any_of": {"type": "array", "items": {"type": "string"}},
+                            "spec": {"type": "string"},
+                            "message": {"type": "string"},
+                            "when": {"type": "string"},
+                        },
+                    },
+                    {"type": "string"},
+                ]
+            },
+        },
+        # Shorthand for a single requirement group with
+        # one member
+        {"type": "string"},
+    ]
+}
+
+permissions = {
+    "type": "object",
+    "additionalProperties": False,
+    "properties": {
+        "read": {"type": "string", "enum": ["user", "group", "world"]},
+        "write": {"type": "string", "enum": ["user", "group", "world"]},
+        "group": {"type": "string"},
+    },
+}
+
+package_attributes = {
+    "type": "object",
+    "additionalProperties": False,
+    "patternProperties": {r"\w+": {}},
+}
 
 #: Properties for inclusion in other schemas
 properties = {
@@ -15,57 +75,14 @@
         "type": "object",
         "default": {},
         "additionalProperties": False,
-        "patternProperties": {
-            r"\w[\w-]*": {  # package name
+        "properties": {
+            "all": {  # package name
                 "type": "object",
                 "default": {},
                 "additionalProperties": False,
                 "properties": {
-                    "require": {
-                        "oneOf": [
-                            # 'require' can be a list of requirement_groups.
-                            # each requirement group is a list of one or more
-                            # specs. Either at least one or exactly one spec
-                            # in the group must be satisfied (depending on
-                            # whether you use "any_of" or "one_of",
-                            # repectively)
-                            {
-                                "type": "array",
-                                "items": {
-                                    "oneOf": [
-                                        {
-                                            "type": "object",
-                                            "additionalProperties": False,
-                                            "properties": {
-                                                "one_of": {
-                                                    "type": "array",
-                                                    "items": {"type": "string"},
-                                                },
-                                                "any_of": {
-                                                    "type": "array",
-                                                    "items": {"type": "string"},
-                                                },
-                                                "spec": {"type": "string"},
-                                                "message": {"type": "string"},
-                                                "when": {"type": "string"},
-                                            },
-                                        },
-                                        {"type": "string"},
-                                    ]
-                                },
-                            },
-                            # Shorthand for a single requirement group with
-                            # one member
-                            {"type": "string"},
-                        ]
-                    },
-                    "version": {
-                        "type": "array",
-                        "default": [],
-                        # version strings (type should be string, number is still possible
-                        # but deprecated. this is to avoid issues with e.g. 3.10 -> 3.1)
-                        "items": {"anyOf": [{"type": "string"}, {"type": "number"}]},
-                    },
+                    "require": requirements,
+                    "version": {},  # Here only to warn users on ignored properties
                     "target": {
                         "type": "array",
                         "default": [],
@@ -78,22 +95,10 @@
                         "items": {"type": "string"},
                     },  # compiler specs
                     "buildable": {"type": "boolean", "default": True},
-                    "permissions": {
-                        "type": "object",
-                        "additionalProperties": False,
-                        "properties": {
-                            "read": {"type": "string", "enum": ["user", "group", "world"]},
-                            "write": {"type": "string", "enum": ["user", "group", "world"]},
-                            "group": {"type": "string"},
-                        },
-                    },
+                    "permissions": permissions,
                     # If 'get_full_repo' is promoted to a Package-level
                     # attribute, it could be useful to set it here
-                    "package_attributes": {
-                        "type": "object",
-                        "additionalProperties": False,
-                        "patternProperties": {r"\w+": {}},
-                    },
+                    "package_attributes": package_attributes,
                     "providers": {
                         "type": "object",
                         "default": {},
@@ -106,12 +111,40 @@
                             }
                         },
                     },
-                    "variants": {
-                        "oneOf": [
-                            {"type": "string"},
-                            {"type": "array", "items": {"type": "string"}},
-                        ]
+                    "variants": variants,
+                },
+                "deprecatedProperties": {
+                    "properties": ["version"],
+                    "message": "setting version preferences in the 'all' section of packages.yaml "
+                    "is deprecated and will be removed in v0.22\n\n\tThese preferences "
+                    "will be ignored by Spack. You can set them only in package specific sections "
+                    "of the same file.\n",
+                    "error": False,
+                },
+            }
+        },
+        "patternProperties": {
+            r"(?!^all$)(^\w[\w-]*)": {  # package name
+                "type": "object",
+                "default": {},
+                "additionalProperties": False,
+                "properties": {
+                    "require": requirements,
+                    "version": {
+                        "type": "array",
+                        "default": [],
+                        # version strings
+                        "items": {"anyOf": [{"type": "string"}, {"type": "number"}]},
                     },
+                    "target": {},  # Here only to warn users on ignored properties
+                    "compiler": {},  # Here only to warn users on ignored properties
+                    "buildable": {"type": "boolean", "default": True},
+                    "permissions": permissions,
+                    # If 'get_full_repo' is promoted to a Package-level
+                    # attribute, it could be useful to set it here
+                    "package_attributes": package_attributes,
+                    "providers": {},  # Here only to warn users on ignored properties
+                    "variants": variants,
                     "externals": {
                         "type": "array",
                         "items": {
@@ -127,6 +160,14 @@
                         },
                     },
                 },
+                "deprecatedProperties": {
+                    "properties": ["target", "compiler", "providers"],
+                    "message": "setting compiler, target or provider preferences in a package "
+                    "specific section of packages.yaml is deprecated, and will be removed in "
+                    "v0.22.\n\n\tThese preferences will be ignored by Spack. You "
+                    "can set them only in the 'all' section of the same file.\n",
+                    "error": False,
+                },
             }
         },
     }

lib/spack/spack/solver/asp.py

@@ -13,7 +13,7 @@
 import re
 import types
 import warnings
-from typing import Dict, List, NamedTuple, Optional, Sequence, Tuple, Union
+from typing import Callable, Dict, List, NamedTuple, Optional, Sequence, Set, Tuple, Union
 
 import archspec.cpu
 
@@ -338,6 +338,13 @@ def __getattr__(self, name):
 
 fn = AspFunctionBuilder()
 
+TransformFunction = Callable[[spack.spec.Spec, List[AspFunction]], List[AspFunction]]
+
+
+def remove_node(spec: spack.spec.Spec, facts: List[AspFunction]) -> List[AspFunction]:
+    """Transformation that removes all "node" and "virtual_node" from the input list of facts."""
+    return list(filter(lambda x: x.args[0] not in ("node", "virtual_node"), facts))
+
 
 def _create_counter(specs, tests):
     strategy = spack.config.CONFIG.get("concretizer:duplicates:strategy", "none")
@@ -685,7 +692,7 @@ def extract_args(model, predicate_name):
 class ErrorHandler:
     def __init__(self, model):
         self.model = model
-        self.error_args = extract_args(model, "error")
+        self.full_model = None
 
     def multiple_values_error(self, attribute, pkg):
         return f'Cannot select a single "{attribute}" for package "{pkg}"'
@@ -693,6 +700,48 @@ def multiple_values_error(self, attribute, pkg):
     def no_value_error(self, attribute, pkg):
         return f'Cannot select a single "{attribute}" for package "{pkg}"'
 
+    def _get_cause_tree(
+        self,
+        cause: Tuple[str, str],
+        conditions: Dict[str, str],
+        condition_causes: List[Tuple[Tuple[str, str], Tuple[str, str]]],
+        seen: Set,
+        indent: str = "        ",
+    ) -> List[str]:
+        """
+        Implementation of recursion for self.get_cause_tree. Much of this operates on tuples
+        (condition_id, set_id) in which the latter idea means that the condition represented by
+        the former held in the condition set represented by the latter.
+        """
+        seen = set(seen) | set(cause)
+        parents = [c for e, c in condition_causes if e == cause and c not in seen]
+        local = "required because %s " % conditions[cause[0]]
+
+        return [indent + local] + [
+            c
+            for parent in parents
+            for c in self._get_cause_tree(
+                parent, conditions, condition_causes, seen, indent=indent + "  "
+            )
+        ]
+
+    def get_cause_tree(self, cause: Tuple[str, str]) -> List[str]:
+        """
+        Get the cause tree associated with the given cause.
+
+        Arguments:
+            cause: The root cause of the tree (final condition)
+
+        Returns:
+            A list of strings describing the causes, formatted to display tree structure.
+        """
+        conditions: Dict[str, str] = dict(extract_args(self.full_model, "condition_reason"))
+        condition_causes: List[Tuple[Tuple[str, str], Tuple[str, str]]] = list(
+            ((Effect, EID), (Cause, CID))
+            for Effect, EID, Cause, CID in extract_args(self.full_model, "condition_cause")
+        )
+        return self._get_cause_tree(cause, conditions, condition_causes, set())
+
     def handle_error(self, msg, *args):
         """Handle an error state derived by the solver."""
         if msg == "multiple_values_error":
@@ -701,14 +750,31 @@ def handle_error(self, msg, *args):
         if msg == "no_value_error":
             return self.no_value_error(*args)
 
+        try:
+            idx = args.index("startcauses")
+        except ValueError:
+            msg_args = args
+            causes = []
+        else:
+            msg_args = args[:idx]
+            cause_args = args[idx + 1 :]
+            cause_args_conditions = cause_args[::2]
+            cause_args_ids = cause_args[1::2]
+            causes = list(zip(cause_args_conditions, cause_args_ids))
+
+        msg = msg.format(*msg_args)
+
         # For variant formatting, we sometimes have to construct specs
         # to format values properly. Find/replace all occurances of
         # Spec(...) with the string representation of the spec mentioned
-        msg = msg.format(*args)
         specs_to_construct = re.findall(r"Spec\(([^)]*)\)", msg)
         for spec_str in specs_to_construct:
             msg = msg.replace("Spec(%s)" % spec_str, str(spack.spec.Spec(spec_str)))
 
+        for cause in set(causes):
+            for c in self.get_cause_tree(cause):
+                msg += f"\n{c}"
+
         return msg
 
     def message(self, errors) -> str:
@@ -720,11 +786,31 @@ def message(self, errors) -> str:
         return "\n".join([header] + messages)
 
     def raise_if_errors(self):
-        if not self.error_args:
+        initial_error_args = extract_args(self.model, "error")
+        if not initial_error_args:
             return
 
+        error_causation = clingo.Control()
+
+        parent_dir = pathlib.Path(__file__).parent
+        errors_lp = parent_dir / "error_messages.lp"
+
+        def on_model(model):
+            self.full_model = model.symbols(shown=True, terms=True)
+
+        with error_causation.backend() as backend:
+            for atom in self.model:
+                atom_id = backend.add_atom(atom)
+                backend.add_rule([atom_id], [], choice=False)
+
+            error_causation.load(str(errors_lp))
+            error_causation.ground([("base", []), ("error_messages", [])])
+            _ = error_causation.solve(on_model=on_model)
+
+        # No choices so there will be only one model
+        error_args = extract_args(self.full_model, "error")
         errors = sorted(
-            [(int(priority), msg, args) for priority, msg, *args in self.error_args], reverse=True
+            [(int(priority), msg, args) for priority, msg, *args in error_args], reverse=True
         )
         msg = self.message(errors)
         raise UnsatisfiableSpecError(msg)
@@ -889,14 +975,6 @@ def on_model(model):
 
         timer.start("solve")
         solve_result = self.control.solve(**solve_kwargs)
-
-        if solve_result.satisfiable and self._model_has_cycles(models):
-            tty.debug(f"cycles detected, falling back to slower algorithm [specs={specs}]")
-            self.control.load(os.path.join(parent_dir, "cycle_detection.lp"))
-            self.control.ground([("no_cycle", [])])
-            models.clear()
-            solve_result = self.control.solve(**solve_kwargs)
-
         timer.stop("solve")
 
         # once done, construct the solve result
@@ -933,7 +1011,7 @@ def on_model(model):
                 if sym.name not in ("attr", "error", "opt_criterion"):
                     tty.debug(
                         "UNKNOWN SYMBOL: %s(%s)"
-                        % (sym.name, ", ".join(intermediate_repr(sym.arguments)))
+                        % (sym.name, ", ".join([str(s) for s in intermediate_repr(sym.arguments)]))
                     )
 
         elif cores:
@@ -950,26 +1028,6 @@ def on_model(model):
 
         return result, timer, self.control.statistics
 
-    def _model_has_cycles(self, models):
-        """Returns true if the best model has cycles in it"""
-        cycle_detection = clingo.Control()
-        parent_dir = pathlib.Path(__file__).parent
-        lp_file = parent_dir / "cycle_detection.lp"
-
-        min_cost, best_model = min(models)
-        with cycle_detection.backend() as backend:
-            for atom in best_model:
-                if atom.name == "attr" and str(atom.arguments[0]) == '"depends_on"':
-                    symbol = fn.depends_on(atom.arguments[1], atom.arguments[2])
-                    atom_id = backend.add_atom(symbol.symbol())
-                    backend.add_rule([atom_id], [], choice=False)
-
-            cycle_detection.load(str(lp_file))
-            cycle_detection.ground([("base", []), ("no_cycle", [])])
-            cycle_result = cycle_detection.solve()
-
-        return cycle_result.unsatisfiable
-
 
 class ConcreteSpecsByHash(collections.abc.Mapping):
     """Mapping containing concrete specs keyed by DAG hash.
@@ -1145,7 +1203,7 @@ def conflict_rules(self, pkg):
         default_msg = "{0}: '{1}' conflicts with '{2}'"
         no_constraint_msg = "{0}: conflicts with '{1}'"
         for trigger, constraints in pkg.conflicts.items():
-            trigger_msg = "conflict trigger %s" % str(trigger)
+            trigger_msg = f"conflict is triggered when {str(trigger)}"
             trigger_spec = spack.spec.Spec(trigger)
             trigger_id = self.condition(
                 trigger_spec, name=trigger_spec.name or pkg.name, msg=trigger_msg
@@ -1157,7 +1215,11 @@ def conflict_rules(self, pkg):
                         conflict_msg = no_constraint_msg.format(pkg.name, trigger)
                     else:
                         conflict_msg = default_msg.format(pkg.name, trigger, constraint)
-                constraint_msg = "conflict constraint %s" % str(constraint)
+
+                spec_for_msg = (
+                    spack.spec.Spec(pkg.name) if constraint == spack.spec.Spec() else constraint
+                )
+                constraint_msg = f"conflict applies to spec {str(spec_for_msg)}"
                 constraint_id = self.condition(constraint, name=pkg.name, msg=constraint_msg)
                 self.gen.fact(
                     fn.pkg_fact(pkg.name, fn.conflict(trigger_id, constraint_id, conflict_msg))
@@ -1196,32 +1258,9 @@ def compiler_facts(self):
         matches = sorted(indexed_possible_compilers, key=lambda x: ppk(x[1].spec))
 
         for weight, (compiler_id, cspec) in enumerate(matches):
-            f = fn.default_compiler_preference(compiler_id, weight)
+            f = fn.compiler_weight(compiler_id, weight)
             self.gen.fact(f)
 
-    def package_compiler_defaults(self, pkg):
-        """Facts about packages' compiler prefs."""
-
-        packages = spack.config.get("packages")
-        pkg_prefs = packages.get(pkg.name)
-        if not pkg_prefs or "compiler" not in pkg_prefs:
-            return
-
-        compiler_list = self.possible_compilers
-        compiler_list = sorted(compiler_list, key=lambda x: (x.name, x.version), reverse=True)
-        ppk = spack.package_prefs.PackagePrefs(pkg.name, "compiler", all=False)
-        matches = sorted(compiler_list, key=lambda x: ppk(x.spec))
-
-        for i, compiler in enumerate(reversed(matches)):
-            self.gen.fact(
-                fn.pkg_fact(
-                    pkg.name,
-                    fn.node_compiler_preference(
-                        compiler.spec.name, compiler.spec.version, -i * 100
-                    ),
-                )
-            )
-
     def package_requirement_rules(self, pkg):
         rules = self.requirement_rules_from_package_py(pkg)
         rules.extend(self.requirement_rules_from_packages_yaml(pkg))
@@ -1313,9 +1352,6 @@ def pkg_rules(self, pkg, tests):
         # conflicts
         self.conflict_rules(pkg)
 
-        # default compilers for this package
-        self.package_compiler_defaults(pkg)
-
         # virtuals
         self.package_provider_rules(pkg)
 
@@ -1339,7 +1375,7 @@ def trigger_rules(self):
         self.gen.h2("Trigger conditions")
         for name in self._trigger_cache:
             cache = self._trigger_cache[name]
-            for spec_str, (trigger_id, requirements) in cache.items():
+            for (spec_str, _), (trigger_id, requirements) in cache.items():
                 self.gen.fact(fn.pkg_fact(name, fn.trigger_id(trigger_id)))
                 self.gen.fact(fn.pkg_fact(name, fn.trigger_msg(spec_str)))
                 for predicate in requirements:
@@ -1352,7 +1388,7 @@ def effect_rules(self):
         self.gen.h2("Imposed requirements")
         for name in self._effect_cache:
             cache = self._effect_cache[name]
-            for spec_str, (effect_id, requirements) in cache.items():
+            for (spec_str, _), (effect_id, requirements) in cache.items():
                 self.gen.fact(fn.pkg_fact(name, fn.effect_id(effect_id)))
                 self.gen.fact(fn.pkg_fact(name, fn.effect_msg(spec_str)))
                 for predicate in requirements:
@@ -1451,18 +1487,26 @@ def variant_rules(self, pkg):
 
             self.gen.newline()
 
-    def condition(self, required_spec, imposed_spec=None, name=None, msg=None, node=False):
+    def condition(
+        self,
+        required_spec: spack.spec.Spec,
+        imposed_spec: Optional[spack.spec.Spec] = None,
+        name: Optional[str] = None,
+        msg: Optional[str] = None,
+        transform_required: Optional[TransformFunction] = None,
+        transform_imposed: Optional[TransformFunction] = remove_node,
+    ):
         """Generate facts for a dependency or virtual provider condition.
 
         Arguments:
-            required_spec (spack.spec.Spec): the spec that triggers this condition
-            imposed_spec (spack.spec.Spec or None): the spec with constraints that
-                are imposed when this condition is triggered
-            name (str or None): name for `required_spec` (required if
-                required_spec is anonymous, ignored if not)
-            msg (str or None): description of the condition
-            node (bool): if False does not emit "node" or "virtual_node" requirements
-                from the imposed spec
+            required_spec: the constraints that triggers this condition
+            imposed_spec: the constraints that are imposed when this condition is triggered
+            name: name for `required_spec` (required if required_spec is anonymous, ignored if not)
+            msg: description of the condition
+            transform_required: transformation applied to facts from the required spec. Defaults
+                to leave facts as they are.
+            transform_imposed: transformation applied to facts from the imposed spec. Defaults
+                to removing "node" and "virtual_node" facts.
         Returns:
             int: id of the condition created by this function
         """
@@ -1480,10 +1524,14 @@ def condition(self, required_spec, imposed_spec=None, name=None, msg=None, node=
 
         cache = self._trigger_cache[named_cond.name]
 
-        named_cond_key = str(named_cond)
+        named_cond_key = (str(named_cond), transform_required)
         if named_cond_key not in cache:
             trigger_id = next(self._trigger_id_counter)
             requirements = self.spec_clauses(named_cond, body=True, required_from=name)
+
+            if transform_required:
+                requirements = transform_required(named_cond, requirements)
+
             cache[named_cond_key] = (trigger_id, requirements)
         trigger_id, requirements = cache[named_cond_key]
         self.gen.fact(fn.pkg_fact(named_cond.name, fn.condition_trigger(condition_id, trigger_id)))
@@ -1492,14 +1540,14 @@ def condition(self, required_spec, imposed_spec=None, name=None, msg=None, node=
             return condition_id
 
         cache = self._effect_cache[named_cond.name]
-        imposed_spec_key = str(imposed_spec)
+        imposed_spec_key = (str(imposed_spec), transform_imposed)
         if imposed_spec_key not in cache:
             effect_id = next(self._effect_id_counter)
             requirements = self.spec_clauses(imposed_spec, body=False, required_from=name)
-            if not node:
-                requirements = list(
-                    filter(lambda x: x.args[0] not in ("node", "virtual_node"), requirements)
-                )
+
+            if transform_imposed:
+                requirements = transform_imposed(imposed_spec, requirements)
+
             cache[imposed_spec_key] = (effect_id, requirements)
         effect_id, requirements = cache[imposed_spec_key]
         self.gen.fact(fn.pkg_fact(named_cond.name, fn.condition_effect(condition_id, effect_id)))
@@ -1530,6 +1578,17 @@ def package_provider_rules(self, pkg):
                 )
             self.gen.newline()
 
+        for when, sets_of_virtuals in pkg.provided_together.items():
+            condition_id = self.condition(
+                when, name=pkg.name, msg="Virtuals are provided together"
+            )
+            for set_id, virtuals_together in enumerate(sets_of_virtuals):
+                for name in virtuals_together:
+                    self.gen.fact(
+                        fn.pkg_fact(pkg.name, fn.provided_together(condition_id, set_id, name))
+                    )
+            self.gen.newline()
+
     def package_dependencies_rules(self, pkg):
         """Translate 'depends_on' directives into ASP logic."""
         for _, conditions in sorted(pkg.dependencies.items()):
@@ -1548,21 +1607,32 @@ def package_dependencies_rules(self, pkg):
                 if not depflag:
                     continue
 
-                msg = "%s depends on %s" % (pkg.name, dep.spec.name)
+                msg = f"{pkg.name} depends on {dep.spec}"
                 if cond != spack.spec.Spec():
-                    msg += " when %s" % cond
+                    msg += f" when {cond}"
                 else:
                     pass
 
-                condition_id = self.condition(cond, dep.spec, pkg.name, msg)
-                self.gen.fact(
-                    fn.pkg_fact(pkg.name, fn.dependency_condition(condition_id, dep.spec.name))
-                )
+                def track_dependencies(input_spec, requirements):
+                    return requirements + [fn.attr("track_dependencies", input_spec.name)]
 
-                for t in dt.ALL_FLAGS:
-                    if t & depflag:
-                        # there is a declared dependency of type t
-                        self.gen.fact(fn.dependency_type(condition_id, dt.flag_to_string(t)))
+                def dependency_holds(input_spec, requirements):
+                    return remove_node(input_spec, requirements) + [
+                        fn.attr(
+                            "dependency_holds", pkg.name, input_spec.name, dt.flag_to_string(t)
+                        )
+                        for t in dt.ALL_FLAGS
+                        if t & depflag
+                    ]
+
+                self.condition(
+                    cond,
+                    dep.spec,
+                    name=pkg.name,
+                    msg=msg,
+                    transform_required=track_dependencies,
+                    transform_imposed=dependency_holds,
+                )
 
                 self.gen.newline()
 
@@ -1577,6 +1647,7 @@ def virtual_preferences(self, pkg_name, func):
             for i, provider in enumerate(providers):
                 provider_name = spack.spec.Spec(provider).name
                 func(vspec, provider_name, i)
+            self.gen.newline()
 
     def provider_defaults(self):
         self.gen.h2("Default virtual providers")
@@ -1657,8 +1728,17 @@ def emit_facts_from_requirement_rules(self, rules: List[RequirementRule]):
                     when_spec = spack.spec.Spec(pkg_name)
 
                 try:
+                    # With virtual we want to emit "node" and "virtual_node" in imposed specs
+                    transform: Optional[TransformFunction] = remove_node
+                    if virtual:
+                        transform = None
+
                     member_id = self.condition(
-                        required_spec=when_spec, imposed_spec=spec, name=pkg_name, node=virtual
+                        required_spec=when_spec,
+                        imposed_spec=spec,
+                        name=pkg_name,
+                        transform_imposed=transform,
+                        msg=f"{spec_str} is a requirement for package {pkg_name}",
                     )
                 except Exception as e:
                     # Do not raise if the rule comes from the 'all' subsection, since usability
@@ -1721,8 +1801,16 @@ def external_packages(self):
             # Declare external conditions with a local index into packages.yaml
             for local_idx, spec in enumerate(external_specs):
                 msg = "%s available as external when satisfying %s" % (spec.name, spec)
-                condition_id = self.condition(spec, msg=msg)
-                self.gen.fact(fn.pkg_fact(pkg_name, fn.possible_external(condition_id, local_idx)))
+
+                def external_imposition(input_spec, _):
+                    return [fn.attr("external_conditions_hold", input_spec.name, local_idx)]
+
+                self.condition(
+                    spec,
+                    spack.spec.Spec(spec.name),
+                    msg=msg,
+                    transform_imposed=external_imposition,
+                )
                 self.possible_versions[spec.name].add(spec.version)
                 self.gen.newline()
 
@@ -1752,8 +1840,8 @@ def preferred_variants(self, pkg_name):
                     fn.variant_default_value_from_packages_yaml(pkg_name, variant.name, value)
                 )
 
-    def target_preferences(self, pkg_name):
-        key_fn = spack.package_prefs.PackagePrefs(pkg_name, "target")
+    def target_preferences(self):
+        key_fn = spack.package_prefs.PackagePrefs("all", "target")
 
         if not self.target_specs_cache:
             self.target_specs_cache = [
@@ -1763,17 +1851,25 @@ def target_preferences(self, pkg_name):
 
         package_targets = self.target_specs_cache[:]
         package_targets.sort(key=key_fn)
-
-        offset = 0
-        best_default = self.default_targets[0][1]
         for i, preferred in enumerate(package_targets):
-            if str(preferred.architecture.target) == best_default and i != 0:
-                offset = 100
-            self.gen.fact(
-                fn.pkg_fact(
-                    pkg_name, fn.target_weight(str(preferred.architecture.target), i + offset)
-                )
-            )
+            self.gen.fact(fn.target_weight(str(preferred.architecture.target), i))
+
+    def flag_defaults(self):
+        self.gen.h2("Compiler flag defaults")
+
+        # types of flags that can be on specs
+        for flag in spack.spec.FlagMap.valid_compiler_flags():
+            self.gen.fact(fn.flag_type(flag))
+        self.gen.newline()
+
+        # flags from compilers.yaml
+        compilers = all_compilers_in_config()
+        for compiler in compilers:
+            for name, flags in compiler.flags.items():
+                for flag in flags:
+                    self.gen.fact(
+                        fn.compiler_version_flag(compiler.name, compiler.version, name, flag)
+                    )
 
     def spec_clauses(self, *args, **kwargs):
         """Wrap a call to `_spec_clauses()` into a try/except block that
@@ -1826,7 +1922,7 @@ class Head:
             node_flag = fn.attr("node_flag_set")
             node_flag_source = fn.attr("node_flag_source")
             node_flag_propagate = fn.attr("node_flag_propagate")
-            variant_propagate = fn.attr("variant_propagate")
+            variant_propagation_candidate = fn.attr("variant_propagation_candidate")
 
         class Body:
             node = fn.attr("node")
@@ -1840,7 +1936,7 @@ class Body:
             node_flag = fn.attr("node_flag")
             node_flag_source = fn.attr("node_flag_source")
             node_flag_propagate = fn.attr("node_flag_propagate")
-            variant_propagate = fn.attr("variant_propagate")
+            variant_propagation_candidate = fn.attr("variant_propagation_candidate")
 
         f = Body if body else Head
 
@@ -1889,7 +1985,9 @@ class Body:
                 clauses.append(f.variant_value(spec.name, vname, value))
 
                 if variant.propagate:
-                    clauses.append(f.variant_propagate(spec.name, vname, value, spec.name))
+                    clauses.append(
+                        f.variant_propagation_candidate(spec.name, vname, value, spec.name)
+                    )
 
                 # Tell the concretizer that this is a possible value for the
                 # variant, to account for things like int/str values where we
@@ -1931,6 +2029,16 @@ class Body:
                 clauses.append(fn.attr("package_hash", spec.name, spec._package_hash))
             clauses.append(fn.attr("hash", spec.name, spec.dag_hash()))
 
+        edges = spec.edges_from_dependents()
+        virtuals = [x for x in itertools.chain.from_iterable([edge.virtuals for edge in edges])]
+        if not body:
+            for virtual in virtuals:
+                clauses.append(fn.attr("provider_set", spec.name, virtual))
+                clauses.append(fn.attr("virtual_node", virtual))
+        else:
+            for virtual in virtuals:
+                clauses.append(fn.attr("virtual_on_incoming_edges", spec.name, virtual))
+
         # add all clauses from dependencies
         if transitive:
             # TODO: Eventually distinguish 2 deps on the same pkg (build and link)
@@ -2217,6 +2325,8 @@ def target_defaults(self, specs):
 
         self.default_targets = list(sorted(set(self.default_targets)))
 
+        self.target_preferences()
+
     def virtual_providers(self):
         self.gen.h2("Virtual providers")
         msg = (
@@ -2538,7 +2648,6 @@ def setup(
             self.pkg_rules(pkg, tests=self.tests)
             self.gen.h2("Package preferences: %s" % pkg)
             self.preferred_variants(pkg)
-            self.target_preferences(pkg)
 
         self.gen.h1("Develop specs")
         # Inject dev_path from environment
@@ -2564,20 +2673,45 @@ def setup(
         self.define_target_constraints()
 
     def literal_specs(self, specs):
-        for idx, spec in enumerate(specs):
+        for spec in specs:
             self.gen.h2("Spec: %s" % str(spec))
-            self.gen.fact(fn.literal(idx))
+            condition_id = next(self._condition_id_counter)
+            trigger_id = next(self._trigger_id_counter)
 
-            self.gen.fact(fn.literal(idx, "virtual_root" if spec.virtual else "root", spec.name))
-            for clause in self.spec_clauses(spec):
-                self.gen.fact(fn.literal(idx, *clause.args))
-                if clause.args[0] == "variant_set":
-                    self.gen.fact(
-                        fn.literal(idx, "variant_default_value_from_cli", *clause.args[1:])
+            # Special condition triggered by "literal_solved"
+            self.gen.fact(fn.literal(trigger_id))
+            self.gen.fact(fn.pkg_fact(spec.name, fn.condition_trigger(condition_id, trigger_id)))
+            self.gen.fact(fn.condition_reason(condition_id, f"{spec} requested from CLI"))
+
+            # Effect imposes the spec
+            imposed_spec_key = str(spec), None
+            cache = self._effect_cache[spec.name]
+            msg = (
+                "literal specs have different requirements. clear cache before computing literals"
+            )
+            assert imposed_spec_key not in cache, msg
+            effect_id = next(self._effect_id_counter)
+            requirements = self.spec_clauses(spec)
+            root_name = spec.name
+            for clause in requirements:
+                clause_name = clause.args[0]
+                if clause_name == "variant_set":
+                    requirements.append(
+                        fn.attr("variant_default_value_from_cli", *clause.args[1:])
                     )
+                elif clause_name in ("node", "virtual_node", "hash"):
+                    # These facts are needed to compute the "condition_set" of the root
+                    pkg_name = clause.args[1]
+                    self.gen.fact(fn.mentioned_in_literal(trigger_id, root_name, pkg_name))
+
+            requirements.append(fn.attr("virtual_root" if spec.virtual else "root", spec.name))
+            cache[imposed_spec_key] = (effect_id, requirements)
+            self.gen.fact(fn.pkg_fact(spec.name, fn.condition_effect(condition_id, effect_id)))
 
             if self.concretize_everything:
-                self.gen.fact(fn.solve_literal(idx))
+                self.gen.fact(fn.solve_literal(trigger_id))
+
+        self.effect_rules()
 
     def validate_and_define_versions_from_requirements(
         self, *, allow_deprecated: bool, require_checksum: bool
@@ -3153,10 +3287,11 @@ def __init__(self, provided, conflicts):
         msg = (
             "Spack concretizer internal error. Please submit a bug report and include the "
             "command, environment if applicable and the following error message."
-            f"\n    {provided} is unsatisfiable, errors are:"
+            f"\n    {provided} is unsatisfiable"
         )
 
-        msg += "".join([f"\n    {conflict}" for conflict in conflicts])
+        if conflicts:
+            msg += ", errors are:" + "".join([f"\n    {conflict}" for conflict in conflicts])
 
         super(spack.error.UnsatisfiableSpecError, self).__init__(msg)
 

lib/spack/spack/solver/concretize.lp

@@ -10,9 +10,8 @@
 % ID of the nodes in the "root" link-run sub-DAG
 #const min_dupe_id = 0.
 
-#const link_run = 0.
-#const direct_link_run =1.
-#const direct_build = 2.
+#const direct_link_run = 0.
+#const direct_build = 1.
 
 % Allow clingo to create nodes
 { attr("node", node(0..X-1, Package))         } :- max_dupes(Package, X), not virtual(Package).
@@ -30,23 +29,21 @@
 :- attr("variant_value", PackageNode, _, _), not attr("node", PackageNode).
 :- attr("node_flag_compiler_default", PackageNode), not attr("node", PackageNode).
 :- attr("node_flag", PackageNode, _, _), not attr("node", PackageNode).
-:- attr("node_flag_source", PackageNode, _, _), not attr("node", PackageNode).
 :- attr("no_flags", PackageNode, _), not attr("node", PackageNode).
 :- attr("external_spec_selected", PackageNode, _), not attr("node", PackageNode).
 :- attr("depends_on", ParentNode, _, _), not attr("node", ParentNode).
 :- attr("depends_on", _, ChildNode, _), not attr("node", ChildNode).
 :- attr("node_flag_source", ParentNode, _, _), not attr("node", ParentNode).
 :- attr("node_flag_source", _, _, ChildNode), not attr("node", ChildNode).
+:- attr("virtual_node", VirtualNode), not provider(_, VirtualNode), internal_error("virtual node with no provider").
+:- provider(_, VirtualNode), not attr("virtual_node", VirtualNode), internal_error("provider with no virtual node").
+:- provider(PackageNode, _), not attr("node", PackageNode), internal_error("provider with no real node").
 
-:- attr("virtual_node", VirtualNode), not provider(_, VirtualNode).
-:- provider(_, VirtualNode), not attr("virtual_node", VirtualNode).
-:- provider(PackageNode, _), not attr("node", PackageNode).
-
-:- attr("root", node(ID, PackageNode)), ID > min_dupe_id.
+:- attr("root", node(ID, PackageNode)), ID > min_dupe_id, internal_error("root with a non-minimal duplicate ID").
 
 % Nodes in the "root" unification set cannot depend on non-root nodes if the dependency is "link" or "run"
-:- attr("depends_on", node(min_dupe_id, Package), node(ID, _), "link"), ID != min_dupe_id, unification_set("root", node(min_dupe_id, Package)).
-:- attr("depends_on", node(min_dupe_id, Package), node(ID, _), "run"),  ID != min_dupe_id, unification_set("root", node(min_dupe_id, Package)).
+:- attr("depends_on", node(min_dupe_id, Package), node(ID, _), "link"), ID != min_dupe_id, unification_set("root", node(min_dupe_id, Package)), internal_error("link dependency out of the root unification set").
+:- attr("depends_on", node(min_dupe_id, Package), node(ID, _), "run"),  ID != min_dupe_id, unification_set("root", node(min_dupe_id, Package)), internal_error("run dependency out of the root unification set").
 
 % Rules on "unification sets", i.e. on sets of nodes allowing a single configuration of any given package
 unify(SetID, PackageName) :- unification_set(SetID, node(_, PackageName)).
@@ -86,22 +83,24 @@ unification_set(SetID, VirtualNode)
 %----
 
 % In the "root" unification set only ID = 0 are allowed
-:- unification_set("root", node(ID, _)), ID != 0.
+:- unification_set("root", node(ID, _)), ID != 0, internal_error("root unification set has node with non-zero unification set ID").
 
 % In the "root" unification set we allow only packages from the link-run possible subDAG
-:- unification_set("root", node(_, Package)), not possible_in_link_run(Package), not virtual(Package).
+:- unification_set("root", node(_, Package)), not possible_in_link_run(Package), not virtual(Package), internal_error("package outside possible link/run graph in root unification set").
 
 % Each node must belong to at least one unification set
-:- attr("node", PackageNode), not unification_set(_, PackageNode).
+:- attr("node", PackageNode), not unification_set(_, PackageNode), internal_error("node belongs to no unification set").
 
 % Cannot have a node with an ID, if lower ID of the same package are not used
 :- attr("node", node(ID1, Package)),
    not attr("node", node(ID2, Package)),
-   max_dupes(Package, X), ID1=0..X-1, ID2=0..X-1, ID2 < ID1.
+   max_dupes(Package, X), ID1=0..X-1, ID2=0..X-1, ID2 < ID1,
+   internal_error("node skipped id number").
 
 :- attr("virtual_node", node(ID1, Package)),
    not attr("virtual_node", node(ID2, Package)),
-   max_dupes(Package, X), ID1=0..X-1, ID2=0..X-1, ID2 < ID1.
+   max_dupes(Package, X), ID1=0..X-1, ID2=0..X-1, ID2 < ID1,
+   internal_error("virtual node skipped id number").
 
 %-----------------------------------------------------------------------------
 % Map literal input specs to facts that drive the solve
@@ -113,26 +112,30 @@ unification_set(SetID, VirtualNode)
 multiple_nodes_attribute("node_flag_source").
 multiple_nodes_attribute("depends_on").
 multiple_nodes_attribute("virtual_on_edge").
+multiple_nodes_attribute("provider_set").
 
-% Map constraint on the literal ID to facts on the node
-attr(Name, node(min_dupe_id, A1))             :- literal(LiteralID, Name, A1), solve_literal(LiteralID).
-attr(Name, node(min_dupe_id, A1), A2)         :- literal(LiteralID, Name, A1, A2), solve_literal(LiteralID).
-attr(Name, node(min_dupe_id, A1), A2, A3)     :- literal(LiteralID, Name, A1, A2, A3), solve_literal(LiteralID), not multiple_nodes_attribute(Name).
-attr(Name, node(min_dupe_id, A1), A2, A3, A4) :- literal(LiteralID, Name, A1, A2, A3, A4), solve_literal(LiteralID).
+trigger_condition_holds(TriggerID, node(min_dupe_id, Package)) :-
+  solve_literal(TriggerID),
+  pkg_fact(Package, condition_trigger(_, TriggerID)),
+  literal(TriggerID).
 
-% Special cases where nodes occur in arguments other than A1
-attr("node_flag_source", node(min_dupe_id, A1), A2, node(min_dupe_id, A3)) :- literal(LiteralID, "node_flag_source", A1, A2, A3), solve_literal(LiteralID).
-attr("depends_on",       node(min_dupe_id, A1), node(min_dupe_id, A2), A3) :- literal(LiteralID, "depends_on",       A1, A2, A3), solve_literal(LiteralID).
+trigger_node(TriggerID, Node, Node) :-
+  trigger_condition_holds(TriggerID, Node),
+  literal(TriggerID).
+
+% Since we trigger the existence of literal nodes from a condition, we need to construct
+% the condition_set/2 manually below
+mentioned_in_literal(Root, Mentioned) :- mentioned_in_literal(TriggerID, Root, Mentioned), solve_literal(TriggerID).
+condition_set(node(min_dupe_id, Root), node(min_dupe_id, Mentioned)) :-  mentioned_in_literal(Root, Mentioned).
 
 % Discriminate between "roots" that have been explicitly requested, and roots that are deduced from "virtual roots"
-explicitly_requested_root(node(min_dupe_id, A1)) :- literal(LiteralID, "root", A1), solve_literal(LiteralID).
+explicitly_requested_root(node(min_dupe_id, Package)) :-
+  solve_literal(TriggerID),
+  trigger_and_effect(Package, TriggerID, EffectID),
+  imposed_constraint(EffectID, "root", Package).
 
 #defined concretize_everything/0.
 #defined literal/1.
-#defined literal/3.
-#defined literal/4.
-#defined literal/5.
-#defined literal/6.
 
 % Attributes for node packages which must have a single value
 attr_single_value("version").
@@ -230,7 +233,8 @@ possible_version_weight(node(ID, Package), Weight)
 
 1 { version_weight(node(ID, Package), Weight) : pkg_fact(Package, version_declared(Version, Weight)) } 1
   :- attr("version", node(ID, Package), Version),
-     attr("node", node(ID, Package)).
+     attr("node", node(ID, Package)),
+     internal_error("version weights must exist and be unique").
 
 % node_version_satisfies implies that exactly one of the satisfying versions
 % is the package's version, and vice versa.
@@ -244,7 +248,8 @@ possible_version_weight(node(ID, Package), Weight)
 % bound on the choice rule to avoid false positives with the error below
 1 { attr("version", node(ID, Package), Version) : pkg_fact(Package, version_satisfies(Constraint, Version)) }
   :- attr("node_version_satisfies", node(ID, Package), Constraint),
-     pkg_fact(Package, version_satisfies(Constraint, _)).
+     pkg_fact(Package, version_satisfies(Constraint, _)),
+     internal_error("must choose a single version to satisfy version constraints").
 
 % More specific error message if the version cannot satisfy some constraint
 % Otherwise covered by `no_version_error` and `versions_conflict_error`.
@@ -357,7 +362,7 @@ imposed_nodes(ConditionID, PackageNode, node(X, A1))
 
 % Conditions that hold impose may impose constraints on other specs
 attr(Name, node(X, A1))             :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1),             imposed_nodes(ID, PackageNode, node(X, A1)).
-attr(Name, node(X, A1), A2)         :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2),         imposed_nodes(ID, PackageNode, node(X, A1)).
+attr(Name, node(X, A1), A2)         :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2),         imposed_nodes(ID, PackageNode, node(X, A1)), not multiple_nodes_attribute(Name).
 attr(Name, node(X, A1), A2, A3)     :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2, A3),     imposed_nodes(ID, PackageNode, node(X, A1)), not multiple_nodes_attribute(Name).
 attr(Name, node(X, A1), A2, A3, A4) :- impose(ID, PackageNode), imposed_constraint(ID, Name, A1, A2, A3, A4), imposed_nodes(ID, PackageNode, node(X, A1)).
 
@@ -368,6 +373,16 @@ attr("node_flag_source", node(X, A1), A2, node(Y, A3))
      imposed_constraint(ID, "node_flag_source", A1, A2, A3),
      condition_set(node(Y, A3), node(X, A1)).
 
+% Provider set is relevant only for literals, since it's the only place where `^[virtuals=foo] bar`
+% might appear in the HEAD of a rule
+attr("provider_set", node(min_dupe_id, Provider), node(min_dupe_id, Virtual))
+  :- solve_literal(TriggerID),
+     trigger_and_effect(_, TriggerID, EffectID),
+     impose(EffectID, _),
+     imposed_constraint(EffectID, "provider_set", Provider, Virtual).
+
+provider(ProviderNode, VirtualNode) :- attr("provider_set", ProviderNode, VirtualNode).
+
 % Here we can't use the condition set because it's a recursive definition, that doesn't define the
 % node index, and leads to unsatisfiability. Hence we say that one and only one node index must
 % satisfy the dependency.
@@ -427,24 +442,11 @@ depends_on(PackageNode, DependencyNode) :- attr("depends_on", PackageNode, Depen
 % concrete. We chop off dependencies for externals, and dependencies of
 % concrete specs don't need to be resolved -- they arise from the concrete
 % specs themselves.
-dependency_holds(node(NodeID, Package), Dependency, Type) :-
-  pkg_fact(Package, dependency_condition(ID, Dependency)),
-  dependency_type(ID, Type),
-  build(node(NodeID, Package)),
-  not external(node(NodeID, Package)),
-  condition_holds(ID, node(NodeID, Package)).
-
-% We cut off dependencies of externals (as we don't really know them).
-% Don't impose constraints on dependencies that don't exist.
-do_not_impose(EffectID, node(NodeID, Package)) :-
-  not dependency_holds(node(NodeID, Package), Dependency, _),
-  attr("node", node(NodeID, Package)),
-  pkg_fact(Package, dependency_condition(ID, Dependency)),
-  pkg_fact(Package, condition_effect(ID, EffectID)).
+attr("track_dependencies", Node) :- build(Node), not external(Node).
 
 % If a dependency holds on a package node, there must be one and only one dependency node satisfying it
 1 { attr("depends_on", PackageNode, node(0..Y-1, Dependency), Type) : max_dupes(Dependency, Y) } 1
-  :- dependency_holds(PackageNode, Dependency, Type),
+  :- attr("dependency_holds", PackageNode, Dependency, Type),
      not virtual(Dependency).
 
 % all nodes in the graph must be reachable from some root
@@ -476,10 +478,25 @@ error(1, Msg)
 % Virtual dependencies
 %-----------------------------------------------------------------------------
 
+% If the provider is set from the command line, its weight is 0
+possible_provider_weight(ProviderNode, VirtualNode, 0, "Set on the command line")
+  :- attr("provider_set", ProviderNode, VirtualNode).
+
+% Enforces all virtuals to be provided, if multiple of them are provided together
+error(100, "Package '{0}' needs to provide both '{1}' and '{2}' together, but provides only '{1}'", Package, Virtual1, Virtual2)
+:- condition_holds(ID, node(X, Package)),
+   pkg_fact(Package, provided_together(ID, SetID, Virtual1)),
+   pkg_fact(Package, provided_together(ID, SetID, Virtual2)),
+   Virtual1 != Virtual2,
+   attr("virtual_on_incoming_edges", node(X, Package), Virtual1),
+   not attr("virtual_on_incoming_edges", node(X, Package), Virtual2),
+   attr("virtual_node", node(_, Virtual1)),
+   attr("virtual_node", node(_, Virtual2)).
+
 % if a package depends on a virtual, it's not external and we have a
 % provider for that virtual then it depends on the provider
 node_depends_on_virtual(PackageNode, Virtual, Type)
-  :- dependency_holds(PackageNode, Virtual, Type),
+  :- attr("dependency_holds", PackageNode, Virtual, Type),
      virtual(Virtual),
      not external(PackageNode).
 
@@ -489,11 +506,14 @@ node_depends_on_virtual(PackageNode, Virtual) :- node_depends_on_virtual(Package
   :- node_depends_on_virtual(PackageNode, Virtual, Type).
 
 attr("virtual_on_edge", PackageNode, ProviderNode, Virtual)
-  :- dependency_holds(PackageNode, Virtual, Type),
+  :- attr("dependency_holds", PackageNode, Virtual, Type),
      attr("depends_on", PackageNode, ProviderNode, Type),
      provider(ProviderNode, node(_, Virtual)),
      not external(PackageNode).
 
+attr("virtual_on_incoming_edges", ProviderNode, Virtual)
+  :- attr("virtual_on_edge", _, ProviderNode, Virtual).
+
 % dependencies on virtuals also imply that the virtual is a virtual node
 1 { attr("virtual_node", node(0..X-1, Virtual)) : max_dupes(Virtual, X) }
   :- node_depends_on_virtual(PackageNode, Virtual).
@@ -501,6 +521,10 @@ attr("virtual_on_edge", PackageNode, ProviderNode, Virtual)
 % If there's a virtual node, we must select one and only one provider.
 % The provider must be selected among the possible providers.
 
+error(100, "'{0}' cannot be a provider for the '{1}' virtual", Package, Virtual)
+  :-  attr("provider_set", node(min_dupe_id, Package), node(min_dupe_id, Virtual)),
+      not virtual_condition_holds( node(min_dupe_id, Package), Virtual).
+
 error(100, "Cannot find valid provider for virtual {0}", Virtual)
   :- attr("virtual_node", node(X, Virtual)),
      not provider(_, node(X, Virtual)).
@@ -521,20 +545,6 @@ attr("root", PackageNode) :- attr("virtual_root", VirtualNode), provider(Package
     attr("node", PackageNode), virtual_condition_holds(PackageNode, Virtual) } 1
   :- attr("virtual_node", node(X, Virtual)).
 
-% If a spec is selected as a provider, it is for all the virtual it could provide
-:- provider(PackageNode, node(X, Virtual1)),
-   virtual_condition_holds(PackageNode, Virtual2),
-   Virtual2 != Virtual1,
-   unification_set(SetID, PackageNode),
-   unification_set(SetID, node(X, Virtual2)),
-   not provider(PackageNode, node(X, Virtual2)).
-
-% If a spec is a dependency, and could provide a needed virtual, it must be a provider
-:- node_depends_on_virtual(PackageNode, Virtual),
-   depends_on(PackageNode, PossibleProviderNode),
-   virtual_condition_holds(PossibleProviderNode, Virtual),
-   not attr("virtual_on_edge", PackageNode, PossibleProviderNode, Virtual).
-
 % The provider provides the virtual if some provider condition holds.
 virtual_condition_holds(node(ProviderID, Provider), Virtual) :- virtual_condition_holds(ID, node(ProviderID, Provider), Virtual).
 virtual_condition_holds(ID, node(ProviderID, Provider), Virtual) :-
@@ -561,6 +571,8 @@ do_not_impose(EffectID, node(X, Package))
    not virtual_condition_holds(PackageNode, Virtual),
    internal_error("Virtual when provides not respected").
 
+#defined provided_together/4.
+
 %-----------------------------------------------------------------------------
 % Virtual dependency weights
 %-----------------------------------------------------------------------------
@@ -577,21 +589,15 @@ possible_provider_weight(DependencyNode, VirtualNode, 0, "external")
   :- provider(DependencyNode, VirtualNode),
      external(DependencyNode).
 
-% A provider mentioned in packages.yaml can use a weight
-% according to its priority in the list of providers
-possible_provider_weight(node(DependencyID, Dependency), node(VirtualID, Virtual), Weight, "packages_yaml")
-  :- provider(node(DependencyID, Dependency), node(VirtualID, Virtual)),
-     depends_on(node(ID, Package), node(DependencyID, Dependency)),
-     pkg_fact(Package, provider_preference(Virtual, Dependency, Weight)).
-
 % A provider mentioned in the default configuration can use a weight
 % according to its priority in the list of providers
-possible_provider_weight(node(DependencyID, Dependency), node(VirtualID, Virtual), Weight, "default")
-  :- provider(node(DependencyID, Dependency), node(VirtualID, Virtual)),
-     default_provider_preference(Virtual, Dependency, Weight).
+possible_provider_weight(node(ProviderID, Provider), node(VirtualID, Virtual), Weight, "default")
+  :- provider(node(ProviderID, Provider), node(VirtualID, Virtual)),
+     default_provider_preference(Virtual, Provider, Weight).
 
 % Any provider can use 100 as a weight, which is very high and discourage its use
-possible_provider_weight(node(DependencyID, Dependency), VirtualNode, 100, "fallback") :- provider(node(DependencyID, Dependency), VirtualNode).
+possible_provider_weight(node(ProviderID, Provider), VirtualNode, 100, "fallback")
+  :- provider(node(ProviderID, Provider), VirtualNode).
 
 % do not warn if generated program contains none of these.
 #defined virtual/1.
@@ -609,11 +615,11 @@ possible_provider_weight(node(DependencyID, Dependency), VirtualNode, 100, "fall
     pkg_fact(Package, version_declared(Version, Weight, "external")) }
     :- external(node(ID, Package)).
 
-error(100, "Attempted to use external for '{0}' which does not satisfy any configured external spec", Package)
+error(100, "Attempted to use external for '{0}' which does not satisfy any configured external spec version", Package)
   :- external(node(ID, Package)),
      not external_version(node(ID, Package), _, _).
 
-error(100, "Attempted to use external for '{0}' which does not satisfy any configured external spec", Package)
+error(100, "Attempted to use external for '{0}' which does not satisfy a unique configured external spec version", Package)
   :- external(node(ID, Package)),
      2 { external_version(node(ID, Package), Version, Weight) }.
 
@@ -642,18 +648,15 @@ external(PackageNode) :- attr("external_spec_selected", PackageNode, _).
 
 % determine if an external spec has been selected
 attr("external_spec_selected", node(ID, Package), LocalIndex) :-
-    external_conditions_hold(node(ID, Package), LocalIndex),
+    attr("external_conditions_hold", node(ID, Package), LocalIndex),
     attr("node", node(ID, Package)),
     not attr("hash", node(ID, Package), _).
 
-external_conditions_hold(node(PackageID, Package), LocalIndex) :-
-    pkg_fact(Package, possible_external(ID, LocalIndex)), condition_holds(ID, node(PackageID, Package)).
-
 % it cannot happen that a spec is external, but none of the external specs
 % conditions hold.
 error(100, "Attempted to use external for '{0}' which does not satisfy any configured external spec", Package)
  :- external(node(ID, Package)),
-    not external_conditions_hold(node(ID, Package), _).
+    not attr("external_conditions_hold", node(ID, Package), _).
 
 %-----------------------------------------------------------------------------
 % Config required semantics
@@ -696,15 +699,18 @@ requirement_group_satisfied(node(ID, Package), X) :-
 % flags if their only source is from a requirement. This is overly-specific
 % and should use a more-generic approach like in https://github.com/spack/spack/pull/37180
 
-{ attr("node_flag", node(ID, A1), A2, A3) } :-
-  requirement_group_member(Y, Package, X),
-  activate_requirement(node(ID, Package), X),
-  imposed_constraint(Y,"node_flag_set", A1, A2, A3).
+{ attr("node_flag", node(ID, Package), FlagType, FlagValue) } :-
+  requirement_group_member(ConditionID, Package, RequirementID),
+  activate_requirement(node(ID, Package), RequirementID),
+  pkg_fact(Package, condition_effect(ConditionID, EffectID)),
+  imposed_constraint(EffectID, "node_flag_set", Package, FlagType, FlagValue).
 
-{ attr("node_flag_source", node(ID, A1), A2, node(ID, A3)) } :-
-  requirement_group_member(Y, Package, X),
-  activate_requirement(node(ID, Package), X),
-  imposed_constraint(Y,"node_flag_source", A1, A2, A3).
+{ attr("node_flag_source", node(NodeID1, Package1), FlagType, node(NodeID2, Package2)) } :-
+  requirement_group_member(ConditionID, Package1, RequirementID),
+  activate_requirement(node(NodeID1, Package1), RequirementID),
+  pkg_fact(Package1, condition_effect(ConditionID, EffectID)),
+  imposed_constraint(EffectID, "node_flag_source", Package1, FlagType, Package2),
+  imposed_nodes(EffectID, node(NodeID2, Package2), node(NodeID1, Package1)).
 
 requirement_weight(node(ID, Package), Group, W) :-
   W = #min {
@@ -751,23 +757,36 @@ node_has_variant(node(ID, Package), Variant) :-
   pkg_fact(Package, variant(Variant)),
   attr("node", node(ID, Package)).
 
-attr("variant_propagate", PackageNode, Variant, Value, Source) :-
+% Variant propagation is forwarded to dependencies
+attr("variant_propagation_candidate", PackageNode, Variant, Value, Source) :-
   attr("node", PackageNode),
   depends_on(ParentNode, PackageNode),
-  attr("variant_propagate", ParentNode, Variant, Value, Source),
-  not attr("variant_set", PackageNode, Variant).
+  attr("variant_value", node(_, Source), Variant, Value),
+  attr("variant_propagation_candidate", ParentNode, Variant, _, Source).
 
-attr("variant_value", node(ID, Package), Variant, Value) :-
-  attr("node", node(ID, Package)),
+% If the node is a candidate, and it has the variant and value,
+% then those variant and value should be propagated
+attr("variant_propagate", node(ID, Package), Variant, Value, Source) :-
+  attr("variant_propagation_candidate", node(ID, Package), Variant, Value, Source),
   node_has_variant(node(ID, Package), Variant),
-  attr("variant_propagate", node(ID, Package), Variant, Value, _),
-  pkg_fact(Package, variant_possible_value(Variant, Value)).
+  pkg_fact(Package, variant_possible_value(Variant, Value)),
+  not attr("variant_set", node(ID, Package), Variant).
 
+% Propagate the value, if there is the corresponding attribute
+attr("variant_value", PackageNode, Variant, Value) :- attr("variant_propagate", PackageNode, Variant, Value, _).
+
+% If a variant is propagated, we cannot have extraneous values (this is for multi valued variants)
+variant_is_propagated(PackageNode, Variant) :- attr("variant_propagate", PackageNode, Variant, _, _).
+:- variant_is_propagated(PackageNode, Variant),
+   attr("variant_value", PackageNode, Variant, Value),
+   not attr("variant_propagate", PackageNode, Variant, Value, _).
+
+% Cannot receive different values from different sources on the same variant
 error(100, "{0} and {1} cannot both propagate variant '{2}' to package {3} with values '{4}' and '{5}'", Source1, Source2, Variant, Package, Value1, Value2) :-
   attr("variant_propagate", node(X, Package), Variant, Value1, Source1),
   attr("variant_propagate", node(X, Package), Variant, Value2, Source2),
   node_has_variant(node(X, Package), Variant),
-  Value1 < Value2.
+  Value1 < Value2, Source1 < Source2.
 
 % a variant cannot be set if it is not a variant on the package
 error(100, "Cannot set variant '{0}' for package '{1}' because the variant condition cannot be satisfied for the given spec", Variant, Package)
@@ -863,13 +882,15 @@ variant_default_not_used(node(ID, Package), Variant, Value)
   :- variant_default_value(Package, Variant, Value),
      node_has_variant(node(ID, Package), Variant),
      not attr("variant_value", node(ID, Package), Variant, Value),
+     not attr("variant_propagate", node(ID, Package), Variant, _, _),
      attr("node", node(ID, Package)).
 
 % The variant is set in an external spec
 external_with_variant_set(node(NodeID, Package), Variant, Value)
  :- attr("variant_value", node(NodeID, Package), Variant, Value),
-    condition_requirement(ID, "variant_value", Package, Variant, Value),
-    pkg_fact(Package, possible_external(ID, _)),
+    condition_requirement(TriggerID, "variant_value", Package, Variant, Value),
+    trigger_and_effect(Package, TriggerID, EffectID),
+    imposed_constraint(EffectID, "external_conditions_hold", Package, _),
     external(node(NodeID, Package)),
     attr("node", node(NodeID, Package)).
 
@@ -1045,7 +1066,7 @@ attr("node_target", PackageNode, Target)
 node_target_weight(node(ID, Package), Weight)
  :- attr("node", node(ID, Package)),
     attr("node_target", node(ID, Package), Target),
-    pkg_fact(Package, target_weight(Target, Weight)).
+    target_weight(Target, Weight).
 
 % compatibility rules for targets among nodes
 node_target_match(ParentNode, DependencyNode)
@@ -1167,23 +1188,17 @@ compiler_mismatch_required(PackageNode, DependencyNode)
 #defined allow_compiler/2.
 
 % compilers weighted by preference according to packages.yaml
-compiler_weight(node(ID, Package), Weight)
+node_compiler_weight(node(ID, Package), Weight)
  :- node_compiler(node(ID, Package), CompilerID),
     compiler_name(CompilerID, Compiler),
     compiler_version(CompilerID, V),
-    pkg_fact(Package, node_compiler_preference(Compiler, V, Weight)).
-compiler_weight(node(ID, Package), Weight)
+    compiler_weight(CompilerID, Weight).
+
+node_compiler_weight(node(ID, Package), 100)
  :- node_compiler(node(ID, Package), CompilerID),
     compiler_name(CompilerID, Compiler),
     compiler_version(CompilerID, V),
-    not pkg_fact(Package, node_compiler_preference(Compiler, V, _)),
-    default_compiler_preference(CompilerID, Weight).
-compiler_weight(node(ID, Package), 100)
- :- node_compiler(node(ID, Package), CompilerID),
-    compiler_name(CompilerID, Compiler),
-    compiler_version(CompilerID, V),
-    not pkg_fact(Package, node_compiler_preference(Compiler, V, _)),
-    not default_compiler_preference(CompilerID, _).
+    not compiler_weight(CompilerID, _).
 
 % For the time being, be strict and reuse only if the compiler match one we have on the system
 error(100, "Compiler {1}@{2} requested for {0} cannot be found. Set install_missing_compilers:true if intended.", Package, Compiler, Version)
@@ -1191,7 +1206,7 @@ error(100, "Compiler {1}@{2} requested for {0} cannot be found. Set install_miss
     not node_compiler(node(ID, Package), _).
 
 #defined node_compiler_preference/4.
-#defined default_compiler_preference/3.
+#defined compiler_weight/3.
 
 %-----------------------------------------------------------------------------
 % Compiler flags
@@ -1325,6 +1340,10 @@ build_priority(PackageNode, 0)   :- not build(PackageNode), attr("node", Package
 
 #defined installed_hash/2.
 
+% This statement, which is a hidden feature of clingo, let us avoid cycles in the DAG
+#edge (A, B) : depends_on(A, B).
+
+
 %-----------------------------------------------------------------
 % Optimization to avoid errors
 %-----------------------------------------------------------------
@@ -1511,7 +1530,7 @@ opt_criterion(15, "non-preferred compilers").
 #minimize{ 0@15: #true }.
 #minimize{
     Weight@15+Priority,PackageNode
-    : compiler_weight(PackageNode, Weight),
+    : node_compiler_weight(PackageNode, Weight),
       build_priority(PackageNode, Priority)
 }.
 

lib/spack/spack/solver/cycle_detection.lp

@@ -1,21 +0,0 @@
-% Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
-% Spack Project Developers. See the top-level COPYRIGHT file for details.
-%
-% SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-%=============================================================================
-% Avoid cycles in the DAG
-%
-% Some combinations of conditional dependencies can result in cycles;
-% this ensures that we solve around them. Note that these rules are quite
-% demanding on both grounding and solving, since they need to compute and
-% consider all possible paths between pair of nodes.
-%=============================================================================
-
-
-#program no_cycle.
-path(Parent, Child) :- depends_on(Parent, Child).
-path(Parent, Descendant) :- path(Parent, A), depends_on(A, Descendant).
-:- path(A, A).
-
-#defined depends_on/2.

lib/spack/spack/solver/display.lp

@@ -24,4 +24,29 @@
 #show error/5.
 #show error/6.
 
+% for error causation
+#show condition_reason/2.
+
+% For error messages to use later
+#show pkg_fact/2.
+#show condition_holds/2.
+#show imposed_constraint/3.
+#show imposed_constraint/4.
+#show imposed_constraint/5.
+#show imposed_constraint/6.
+#show condition_requirement/3.
+#show condition_requirement/4.
+#show condition_requirement/5.
+#show condition_requirement/6.
+#show node_has_variant/2.
+#show build/1.
+#show external/1.
+#show external_version/3.
+#show trigger_and_effect/3.
+#show unification_set/2.
+#show provider/2.
+#show condition_nodes/3.
+#show trigger_node/3.
+#show imposed_nodes/3.
+
 % debug

lib/spack/spack/solver/error_messages.lp

@@ -0,0 +1,239 @@
+% Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+% Spack Project Developers. See the top-level COPYRIGHT file for details.
+%
+% SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+%=============================================================================
+% This logic program adds detailed error messages to Spack's concretizer
+%=============================================================================
+
+#program error_messages.
+
+% Create a causal tree between trigger conditions by locating the effect conditions
+% that are triggers for another condition. Condition2 is caused by Condition1
+condition_cause(Condition2, ID2, Condition1, ID1) :-
+  condition_holds(Condition2, node(ID2, Package2)),
+  pkg_fact(Package2, condition_trigger(Condition2, Trigger)),
+  condition_requirement(Trigger, Name, Package),
+  condition_nodes(Trigger, TriggerNode, node(ID, Package)),
+  trigger_node(Trigger, TriggerNode, node(ID2, Package2)),
+  attr(Name, node(ID, Package)),
+  condition_holds(Condition1, node(ID1, Package1)),
+  pkg_fact(Package1, condition_effect(Condition1, Effect)),
+  imposed_constraint(Effect, Name, Package),
+  imposed_nodes(Effect, node(ID1, Package1), node(ID, Package)).
+
+condition_cause(Condition2, ID2, Condition1, ID1) :-
+  condition_holds(Condition2, node(ID2, Package2)),
+  pkg_fact(Package2, condition_trigger(Condition2, Trigger)),
+  condition_requirement(Trigger, Name, Package, A1),
+  condition_nodes(Trigger, TriggerNode, node(ID, Package)),
+  trigger_node(Trigger, TriggerNode, node(ID2, Package2)),
+  attr(Name, node(ID, Package), A1),
+  condition_holds(Condition1, node(ID1, Package1)),
+  pkg_fact(Package1, condition_effect(Condition1, Effect)),
+  imposed_constraint(Effect, Name, Package, A1),
+  imposed_nodes(Effect, node(ID1, Package1), node(ID, Package)).
+
+condition_cause(Condition2, ID2, Condition1, ID1) :-
+  condition_holds(Condition2, node(ID2, Package2)),
+  pkg_fact(Package2, condition_trigger(Condition2, Trigger)),
+  condition_requirement(Trigger, Name, Package, A1, A2),
+  condition_nodes(Trigger, TriggerNode, node(ID, Package)),
+  trigger_node(Trigger, TriggerNode, node(ID2, Package2)),
+  attr(Name, node(ID, Package), A1, A2),
+  condition_holds(Condition1, node(ID1, Package1)),
+  pkg_fact(Package1, condition_effect(Condition1, Effect)),
+  imposed_constraint(Effect, Name, Package, A1, A2),
+  imposed_nodes(Effect, node(ID1, Package1), node(ID, Package)).
+
+condition_cause(Condition2, ID2, Condition1, ID1) :-
+  condition_holds(Condition2, node(ID2, Package2)),
+  pkg_fact(Package2, condition_trigger(Condition2, Trigger)),
+  condition_requirement(Trigger, Name, Package, A1, A2, A3),
+  condition_nodes(Trigger, TriggerNode, node(ID, Package)),
+  trigger_node(Trigger, TriggerNode, node(ID2, Package2)),
+  attr(Name, node(ID, Package), A1, A2, A3),
+  condition_holds(Condition1, node(ID1, Package1)),
+  pkg_fact(Package1, condition_effect(Condition1, Effect)),
+  imposed_constraint(Effect, Name, Package, A1, A2, A3),
+  imposed_nodes(Effect, node(ID1, Package1), node(ID, Package)).
+
+% special condition cause for dependency conditions
+% we can't simply impose the existence of the node for dependency conditions
+% because we need to allow for the choice of which dupe ID the node gets
+condition_cause(Condition2, ID2, Condition1, ID1) :-
+  condition_holds(Condition2, node(ID2, Package2)),
+  pkg_fact(Package2, condition_trigger(Condition2, Trigger)),
+  condition_requirement(Trigger, "node", Package),
+  condition_nodes(Trigger, TriggerNode, node(ID, Package)),
+  trigger_node(Trigger, TriggerNode, node(ID2, Package2)),
+  attr("node", node(ID, Package)),
+  condition_holds(Condition1, node(ID1, Package1)),
+  pkg_fact(Package1, condition_effect(Condition1, Effect)),
+  imposed_constraint(Effect, "dependency_holds", Parent, Package, Type),
+  imposed_nodes(Effect, node(ID1, Package1), node(ID, Package)),
+  attr("depends_on", node(X, Parent), node(ID, Package), Type).
+
+% The literal startcauses is used to separate the variables that are part of the error from the
+% ones describing the causal tree of the error. After startcauses, each successive pair must be
+% a condition and a condition_set id for which it holds.
+
+% More specific error message if the version cannot satisfy some constraint
+% Otherwise covered by `no_version_error` and `versions_conflict_error`.
+error(1, "Cannot satisfy '{0}@{1}'", Package, Constraint, startcauses, ConstraintCause, CauseID)
+  :- attr("node_version_satisfies", node(ID, Package), Constraint),
+     pkg_fact(TriggerPkg, condition_effect(ConstraintCause, EffectID)),
+     imposed_constraint(EffectID, "node_version_satisfies", Package, Constraint),
+     condition_holds(ConstraintCause, node(CauseID, TriggerPkg)),
+     attr("version", node(ID, Package), Version),
+     not pkg_fact(Package, version_satisfies(Constraint, Version)).
+
+error(0, "Cannot satisfy '{0}@{1}' and '{0}@{2}", Package, Constraint1, Constraint2, startcauses, Cause1, C1ID, Cause2, C2ID)
+  :- attr("node_version_satisfies", node(ID, Package), Constraint1),
+     pkg_fact(TriggerPkg1, condition_effect(Cause1, EffectID1)),
+     imposed_constraint(EffectID1, "node_version_satisfies", Package, Constraint1),
+     condition_holds(Cause1, node(C1ID, TriggerPkg1)),
+     % two constraints
+     attr("node_version_satisfies", node(ID, Package), Constraint2),
+     pkg_fact(TriggerPkg2, condition_effect(Cause2, EffectID2)),
+     imposed_constraint(EffectID2, "node_version_satisfies", Package, Constraint2),
+     condition_holds(Cause2, node(C2ID, TriggerPkg2)),
+     % version chosen
+     attr("version", node(ID, Package), Version),
+     % version satisfies one but not the other
+     pkg_fact(Package, version_satisfies(Constraint1, Version)),
+     not pkg_fact(Package, version_satisfies(Constraint2, Version)).
+
+% causation tracking error for no or multiple virtual providers
+error(0, "Cannot find a valid provider for virtual {0}", Virtual, startcauses, Cause, CID)
+  :- attr("virtual_node", node(X, Virtual)),
+     not provider(_, node(X, Virtual)),
+     imposed_constraint(EID, "dependency_holds", Parent, Virtual, Type),
+     pkg_fact(TriggerPkg, condition_effect(Cause, EID)),
+     condition_holds(Cause, node(CID, TriggerPkg)).
+
+
+% At most one variant value for single-valued variants
+error(0, "'{0}' required multiple values for single-valued variant '{1}'\n    Requested 'Spec({1}={2})' and 'Spec({1}={3})'", Package, Variant, Value1, Value2, startcauses, Cause1, X, Cause2, X)
+  :- attr("node", node(X, Package)),
+     node_has_variant(node(X, Package), Variant),
+     pkg_fact(Package, variant_single_value(Variant)),
+     build(node(X, Package)),
+     attr("variant_value", node(X, Package), Variant, Value1),
+     imposed_constraint(EID1, "variant_set", Package, Variant, Value1),
+     pkg_fact(TriggerPkg1, condition_effect(Cause1, EID1)),
+     condition_holds(Cause1, node(X, TriggerPkg1)),
+     attr("variant_value", node(X, Package), Variant, Value2),
+     imposed_constraint(EID2, "variant_set", Package, Variant, Value2),
+     pkg_fact(TriggerPkg2, condition_effect(Cause2, EID2)),
+     condition_holds(Cause2, node(X, TriggerPkg2)),
+     Value1 < Value2. % see[1] in concretize.lp
+
+% Externals have to specify external conditions
+error(0, "Attempted to use external for {0} which does not satisfy any configured external spec version", Package, startcauses, ExternalCause, CID)
+  :- external(node(ID, Package)),
+     attr("external_spec_selected", node(ID, Package), Index),
+     imposed_constraint(EID, "external_conditions_hold", Package, Index),
+     pkg_fact(TriggerPkg, condition_effect(ExternalCause, EID)),
+     condition_holds(ExternalCause, node(CID, TriggerPkg)),
+     not external_version(node(ID, Package), _, _).
+
+error(0, "Attempted to build package {0} which is not buildable and does not have a satisfying external\n        attr('{1}', '{2}') is an external constraint for {0} which was not satisfied", Package, Name, A1)
+  :- external(node(ID, Package)),
+     not attr("external_conditions_hold", node(ID, Package), _),
+     imposed_constraint(EID, "external_conditions_hold", Package, _),
+     trigger_and_effect(Package, TID, EID),
+     condition_requirement(TID, Name, A1),
+     not attr(Name, node(_, A1)).
+
+error(0, "Attempted to build package {0} which is not buildable and does not have a satisfying external\n        attr('{1}', '{2}', '{3}') is an external constraint for {0} which was not satisfied", Package, Name, A1, A2)
+  :- external(node(ID, Package)),
+     not attr("external_conditions_hold", node(ID, Package), _),
+     imposed_constraint(EID, "external_conditions_hold", Package, _),
+     trigger_and_effect(Package, TID, EID),
+     condition_requirement(TID, Name, A1, A2),
+     not attr(Name, node(_, A1), A2).
+
+error(0, "Attempted to build package {0} which is not buildable and does not have a satisfying external\n        attr('{1}', '{2}', '{3}', '{4}') is an external constraint for {0} which was not satisfied", Package, Name, A1, A2, A3)
+  :- external(node(ID, Package)),
+     not attr("external_conditions_hold", node(ID, Package), _),
+     imposed_constraint(EID, "external_conditions_hold", Package, _),
+     trigger_and_effect(Package, TID, EID),
+     condition_requirement(TID, Name, A1, A2, A3),
+     not attr(Name, node(_, A1), A2, A3).
+
+error(0, "Attempted to build package {0} which is not buildable and does not have a satisfying external\n        'Spec({0} {1}={2})' is an external constraint for {0} which was not satisfied\n        'Spec({0} {1}={3})' required", Package, Variant, Value, OtherValue, startcauses, OtherValueCause, CID)
+  :- external(node(ID, Package)),
+     not attr("external_conditions_hold", node(ID, Package), _),
+     imposed_constraint(EID, "external_conditions_hold", Package, _),
+     trigger_and_effect(Package, TID, EID),
+     condition_requirement(TID, "variant_value", Package, Variant, Value),
+     not attr("variant_value", node(ID, Package), Variant, Value),
+     attr("variant_value", node(ID, Package), Variant, OtherValue),
+     imposed_constraint(EID2, "variant_set", Package, Variant, OtherValue),
+     pkg_fact(TriggerPkg, condition_effect(OtherValueCause, EID2)),
+     condition_holds(OtherValueCause, node(CID, TriggerPkg)).
+
+error(0, "Attempted to build package {0} which is not buildable and does not have a satisfying external\n        attr('{1}', '{2}', '{3}', '{4}', '{5}') is an external constraint for {0} which was not satisfied", Package, Name, A1, A2, A3, A4)
+  :- external(node(ID, Package)),
+     not attr("external_conditions_hold", node(ID, Package), _),
+     imposed_constraint(EID, "external_conditions_hold", Package, _),
+     trigger_and_effect(Package, TID, EID),
+     condition_requirement(TID, Name, A1, A2, A3, A4),
+     not attr(Name, node(_, A1), A2, A3, A4).
+
+% error message with causes for conflicts
+error(0, Msg, startcauses, TriggerID, ID1, ConstraintID, ID2)
+  :- attr("node", node(ID, Package)),
+     pkg_fact(Package, conflict(TriggerID, ConstraintID, Msg)),
+     % node(ID1, TriggerPackage) is node(ID2, Package) in most, but not all, cases
+     condition_holds(TriggerID, node(ID1, TriggerPackage)),
+     condition_holds(ConstraintID, node(ID2, Package)),
+     unification_set(X, node(ID2, Package)),
+     unification_set(X, node(ID1, TriggerPackage)),
+     not external(node(ID, Package)),  % ignore conflicts for externals
+     not attr("hash", node(ID, Package), _).  % ignore conflicts for installed packages
+
+% variables to show
+#show error/2.
+#show error/3.
+#show error/4.
+#show error/5.
+#show error/6.
+#show error/7.
+#show error/8.
+#show error/9.
+#show error/10.
+#show error/11.
+
+#show condition_cause/4.
+#show condition_reason/2.
+
+% Define all variables used to avoid warnings at runtime when the model doesn't happen to have one
+#defined error/2.
+#defined error/3.
+#defined error/4.
+#defined error/5.
+#defined error/6.
+#defined attr/2.
+#defined attr/3.
+#defined attr/4.
+#defined attr/5.
+#defined pkg_fact/2.
+#defined imposed_constraint/3.
+#defined imposed_constraint/4.
+#defined imposed_constraint/5.
+#defined imposed_constraint/6.
+#defined condition_requirement/3.
+#defined condition_requirement/4.
+#defined condition_requirement/5.
+#defined condition_requirement/6.
+#defined condition_holds/2.
+#defined unification_set/2.
+#defined external/1.
+#defined trigger_and_effect/3.
+#defined build/1.
+#defined node_has_variant/2.
+#defined provider/2.
+#defined external_version/3.

lib/spack/spack/solver/heuristic.lp

@@ -11,19 +11,14 @@
 %-----------------
 % Domain heuristic
 %-----------------
-#heuristic attr("hash", node(0, Package), Hash) : literal(_, "root", Package). [45, init]
-#heuristic attr("root", node(0, Package)) : literal(_, "root", Package). [45, true]
-#heuristic attr("node", node(0, Package)) : literal(_, "root", Package). [45, true]
-#heuristic attr("node", node(0, Package)) : literal(_, "node", Package). [45, true]
 
 % Root node
 #heuristic attr("version", node(0, Package), Version) : pkg_fact(Package, version_declared(Version, 0)), attr("root", node(0, Package)). [35, true]
 #heuristic version_weight(node(0, Package), 0) : pkg_fact(Package, version_declared(Version, 0)), attr("root", node(0, Package)). [35, true]
 #heuristic attr("variant_value", node(0, Package), Variant, Value) : variant_default_value(Package, Variant, Value), attr("root", node(0, Package)). [35, true]
-#heuristic attr("node_target", node(0, Package), Target) : pkg_fact(Package, target_weight(Target, 0)), attr("root", node(0, Package)). [35, true]
+#heuristic attr("node_target", node(0, Package), Target) : target_weight(Target, 0), attr("root", node(0, Package)). [35, true]
 #heuristic node_target_weight(node(0, Package), 0) : attr("root", node(0, Package)). [35, true]
-#heuristic node_compiler(node(0, Package), CompilerID) : default_compiler_preference(ID, 0), compiler_id(ID), attr("root", node(0, Package)). [35, true]
+#heuristic node_compiler(node(0, Package), CompilerID) : compiler_weight(ID, 0), compiler_id(ID), attr("root", node(0, Package)). [35, true]
 
 % Providers
 #heuristic attr("node", node(0, Package)) : default_provider_preference(Virtual, Package, 0), possible_in_link_run(Package). [30, true]
-

lib/spack/spack/solver/heuristic_separate.lp

@@ -13,7 +13,7 @@
 #heuristic attr("variant_value", node(ID, Package), Variant, Value) : variant_default_value(Package, Variant, Value), attr("node", node(ID, Package)), ID > 0. [25-5*ID, true]
 #heuristic attr("node_target", node(ID, Package), Target) : pkg_fact(Package, target_weight(Target, 0)), attr("node", node(ID, Package)), ID > 0. [25-5*ID, true]
 #heuristic node_target_weight(node(ID, Package), 0) : attr("node", node(ID, Package)), ID > 0. [25-5*ID, true]
-#heuristic node_compiler(node(ID, Package), CompilerID) : default_compiler_preference(CompilerID, 0), compiler_id(CompilerID), attr("node", node(ID, Package)), ID > 0. [25-5*ID, true]
+#heuristic node_compiler(node(ID, Package), CompilerID) : compiler_weight(CompilerID, 0), compiler_id(CompilerID), attr("node", node(ID, Package)), ID > 0. [25-5*ID, true]
 
 % node(ID, _), split build dependencies
 #heuristic attr("version", node(ID, Package), Version) : pkg_fact(Package, version_declared(Version, 0)), attr("node", node(ID, Package)), multiple_unification_sets(Package), ID > 0. [25, true]
@@ -21,4 +21,4 @@
 #heuristic attr("variant_value", node(ID, Package), Variant, Value) : variant_default_value(Package, Variant, Value), attr("node", node(ID, Package)), multiple_unification_sets(Package), ID > 0. [25, true]
 #heuristic attr("node_target", node(ID, Package), Target) : pkg_fact(Package, target_weight(Target, 0)), attr("node", node(ID, Package)), multiple_unification_sets(Package), ID > 0. [25, true]
 #heuristic node_target_weight(node(ID, Package), 0) : attr("node", node(ID, Package)), multiple_unification_sets(Package), ID > 0. [25, true]
-#heuristic node_compiler(node(ID, Package), CompilerID) : default_compiler_preference(CompilerID, 0), compiler_id(CompilerID), attr("node", node(ID, Package)), multiple_unification_sets(Package), ID > 0. [25, true]
+#heuristic node_compiler(node(ID, Package), CompilerID) : compiler_weight(CompilerID, 0), compiler_id(CompilerID), attr("node", node(ID, Package)), multiple_unification_sets(Package), ID > 0. [25, true]