commands: add support for paged output

Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>

.flake8

@@ -28,7 +28,7 @@ max-line-length = 99
 # - F821: undefined name `name`
 #
 per-file-ignores =
-  var/spack/repos/*/package.py:F403,F405,F821
+  var/spack/*/package.py:F403,F405,F821
   *-ci-package.py:F403,F405,F821
 
 # exclude things we usually do not want linting for.

.github/workflows/ci.yaml

@@ -42,17 +42,17 @@ jobs:
           # built-in repository or documentation
           filters: |
             bootstrap:
-            - 'var/spack/repos/builtin/packages/clingo-bootstrap/**'
-            - 'var/spack/repos/builtin/packages/clingo/**'
-            - 'var/spack/repos/builtin/packages/python/**'
-            - 'var/spack/repos/builtin/packages/re2c/**'
-            - 'var/spack/repos/builtin/packages/gnupg/**'
-            - 'var/spack/repos/builtin/packages/libassuan/**'
-            - 'var/spack/repos/builtin/packages/libgcrypt/**'
-            - 'var/spack/repos/builtin/packages/libgpg-error/**'
-            - 'var/spack/repos/builtin/packages/libksba/**'
-            - 'var/spack/repos/builtin/packages/npth/**'
-            - 'var/spack/repos/builtin/packages/pinentry/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/clingo-bootstrap/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/clingo/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/python/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/re2c/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/gnupg/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/libassuan/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/libgcrypt/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/libgpg-error/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/libksba/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/npth/**'
+            - 'var/spack/repos/spack_repo/builtin/packages/pinentry/**'
             - 'lib/spack/**'
             - 'share/spack/**'
             - '.github/workflows/bootstrap.yml'

.github/workflows/prechecks.yml

@@ -34,7 +34,7 @@ jobs:
         vermin --backport importlib --backport argparse --violations --backport typing -t=3.6- -vvv lib/spack/spack/ lib/spack/llnl/ bin/
     - name: vermin (Repositories)
       run: |
-        vermin --backport importlib --backport argparse --violations --backport typing -t=3.6- -vvv var/spack/repos
+        vermin --backport importlib --backport argparse --violations --backport typing -t=3.6- -vvv var/spack/repos var/spack/test_repos
 
   # Run style checks on the files that have been changed
   style:
@@ -65,7 +65,11 @@ jobs:
       python_version: '3.13'
 
   verify-checksums:
-    if: ${{ inputs.with_packages == 'true' }}
+    # do not run if the commit message or PR description contains [skip-verify-checksums]
+    if: >-
+      ${{ inputs.with_packages == 'true' &&
+      !contains(github.event.pull_request.body, '[skip-verify-checksums]') &&
+      !contains(github.event.head_commit.message, '[skip-verify-checksums]') }}
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29

.github/workflows/requirements/style/requirements.txt

@@ -5,4 +5,4 @@ isort==6.0.1
 mypy==1.15.0
 types-six==1.17.0.20250403
 vermin==1.6.0
-pylint==3.3.6
+pylint==3.3.7

etc/spack/defaults/config.yaml

@@ -178,6 +178,10 @@ config:
   package_lock_timeout: null
 
 
+  # pager(s) to use for commands with potentially long output (e.g., spack info)
+  pager:
+    - less -FXRS
+
   # Control how shared libraries are located at runtime on Linux. See the
   # the Spack documentation for details.
   shared_linking:

etc/spack/defaults/repos.yaml

@@ -11,4 +11,4 @@
 #   ~/.spack/repos.yaml
 # -------------------------------------------------------------------------
 repos:
-  - $spack/var/spack/repos/builtin
+  - $spack/var/spack/repos/spack_repo/builtin

lib/spack/docs/basic_usage.rst

@@ -1916,7 +1916,7 @@ diagnostics. Issues, if found, are reported to stdout:
    PKG-DIRECTIVES: 1 issue found
    1. lammps: wrong variant in "conflicts" directive
        the variant 'adios' does not exist
-       in /home/spack/spack/var/spack/repos/builtin/packages/lammps/package.py
+       in /home/spack/spack/var/spack/repos/spack_repo/builtin/packages/lammps/package.py
 
 
 ------------

lib/spack/docs/build_systems.rst

@@ -83,7 +83,7 @@ packages. You can quickly find examples by running:
 
 .. code-block:: console
 
-   $ cd var/spack/repos/builtin/packages
+   $ cd var/spack/repos/spack_repo/builtin/packages
    $ grep -l QMakePackage */package.py
 
 

lib/spack/docs/build_systems/bundlepackage.rst

@@ -27,10 +27,10 @@ it could use the ``require`` directive as follows:
 
 Spack has a number of built-in bundle packages, such as:
 
-* `AmdAocl <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/amd-aocl/package.py>`_
-* `EcpProxyApps <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/ecp-proxy-apps/package.py>`_
-* `Libc <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/libc/package.py>`_
-* `Xsdk <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/xsdk/package.py>`_
+* `AmdAocl <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/amd_aocl/package.py>`_
+* `EcpProxyApps <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/ecp_proxy_apps/package.py>`_
+* `Libc <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/libc/package.py>`_
+* `Xsdk <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/xsdk/package.py>`_
 
 where ``Xsdk`` also inherits from ``CudaPackage`` and ``RocmPackage`` and
 ``Libc`` is a virtual bundle package for the C standard library.

lib/spack/docs/build_systems/cmakepackage.rst

@@ -199,7 +199,7 @@ a variant to control this:
 However, not every CMake package accepts all four of these options.
 Grep the ``CMakeLists.txt`` file to see if the default values are
 missing or replaced. For example, the
-`dealii <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/dealii/package.py>`_
+`dealii <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/dealii/package.py>`_
 package overrides the default variant with:
 
 .. code-block:: python

lib/spack/docs/build_systems/custompackage.rst

@@ -20,8 +20,8 @@ start is to look at the definitions of other build systems. This guide
 focuses mostly on how Spack's build systems work.
 
 In this guide, we will be using the
-`perl <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/perl/package.py>`_ and
-`cmake <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/cmake/package.py>`_
+`perl <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/perl/package.py>`_ and
+`cmake <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/cmake/package.py>`_
 packages as examples. ``perl``'s build system is a hand-written
 ``Configure`` shell script, while ``cmake`` bootstraps itself during
 installation. Both of these packages require custom build systems.

lib/spack/docs/build_systems/makefilepackage.rst

@@ -96,9 +96,9 @@ there are any other variables you need to set, you can do this in the
        env.set("BLASLIB", spec["blas"].libs.ld_flags)
 
 
-`cbench <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/cbench/package.py>`_
+`cbench <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/cbench/package.py>`_
 is a good example of a simple package that does this, while
-`esmf <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/esmf/package.py>`_
+`esmf <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/esmf/package.py>`_
 is a good example of a more complex package.
 
 """"""""""""""""""""""
@@ -129,7 +129,7 @@ If you do need access to the spec, you can create a property like so:
        ]
 
 
-`cloverleaf <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/cloverleaf/package.py>`_
+`cloverleaf <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/cloverleaf/package.py>`_
 is a good example of a package that uses this strategy.
 
 """""""""""""
@@ -152,7 +152,7 @@ and a ``filter`` method to help with this. For example:
        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>`_
+`stream <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/stream/package.py>`_
 is a good example of a package that involves editing a Makefile to set
 the appropriate variables.
 
@@ -192,7 +192,7 @@ well for storing variables:
                inc.write(f"{key} = {config[key]}\n")
 
 
-`elk <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/elk/package.py>`_
+`elk <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/elk/package.py>`_
 is a good example of a package that uses a dictionary to store
 configuration variables.
 
@@ -213,7 +213,7 @@ them in a list:
                inc.write(f"{var}\n")
 
 
-`hpl <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/hpl/package.py>`_
+`hpl <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/hpl/package.py>`_
 is a good example of a package that uses a list to store
 configuration variables.
 

lib/spack/docs/build_systems/rpackage.rst

@@ -39,7 +39,7 @@ for "CRAN <package-name>" and you should quickly find what you want.
 If it isn't on CRAN, try Bioconductor, another common R repository.
 
 For the purposes of this tutorial, we will be walking through
-`r-caret <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/r-caret/package.py>`_
+`r-caret <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/r_caret/package.py>`_
 as an example. If you search for "CRAN caret", you will quickly find what
 you are looking for at https://cran.r-project.org/package=caret.
 https://cran.r-project.org is the main CRAN website. However, CRAN also
@@ -337,7 +337,7 @@ Non-R dependencies
 ^^^^^^^^^^^^^^^^^^
 
 Some packages depend on non-R libraries for linking. Check out the
-`r-stringi <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/r-stringi/package.py>`_
+`r-stringi <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/r_stringi/package.py>`_
 package for an example: https://cloud.r-project.org/package=stringi.
 If you search for the text "SystemRequirements", you will see:
 
@@ -352,7 +352,7 @@ Passing arguments to the installation
 
 Some R packages provide additional flags that can be passed to
 ``R CMD INSTALL``, often to locate non-R dependencies.
-`r-rmpi <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/r-rmpi/package.py>`_
+`r-rmpi <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/r_rmpi/package.py>`_
 is an example of this, and flags for linking to an MPI library. To pass
 these to the installation command, you can override ``configure_args``
 like so:

lib/spack/docs/build_systems/sconspackage.rst

@@ -104,10 +104,10 @@ Finding available options
 
 The first place to start when looking for a list of valid options to
 build a package is ``scons --help``. Some packages like
-`kahip <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/kahip/package.py>`_
+`kahip <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/kahip/package.py>`_
 don't bother overwriting the default SCons help message, so this isn't
 very useful, but other packages like
-`serf <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/serf/package.py>`_
+`serf <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/serf/package.py>`_
 print a list of valid command-line variables:
 
 .. code-block:: console
@@ -177,7 +177,7 @@ print a list of valid command-line variables:
 
 
 More advanced packages like
-`cantera <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/cantera/package.py>`_
+`cantera <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/cantera/package.py>`_
 use ``scons --help`` to print a list of subcommands:
 
 .. code-block:: console

lib/spack/docs/conf.py

@@ -225,10 +225,14 @@ def setup(sphinx):
     ("py:class", "llnl.util.lang.T"),
     ("py:class", "llnl.util.lang.KT"),
     ("py:class", "llnl.util.lang.VT"),
+    ("py:class", "llnl.util.lang.K"),
+    ("py:class", "llnl.util.lang.V"),
     ("py:class", "llnl.util.lang.ClassPropertyType"),
     ("py:obj", "llnl.util.lang.KT"),
     ("py:obj", "llnl.util.lang.VT"),
     ("py:obj", "llnl.util.lang.ClassPropertyType"),
+    ("py:obj", "llnl.util.lang.K"),
+    ("py:obj", "llnl.util.lang.V"),
 ]
 
 # The reST default role (used for this markup: `text`) to use for all documents.

lib/spack/docs/contribution_guide.rst

@@ -226,9 +226,9 @@ If all is well, you'll see something like this:
 
    Modified files:
 
-     var/spack/repos/builtin/packages/hdf5/package.py
-     var/spack/repos/builtin/packages/hdf/package.py
-     var/spack/repos/builtin/packages/netcdf/package.py
+     var/spack/repos/spack_repo/builtin/packages/hdf5/package.py
+     var/spack/repos/spack_repo/builtin/packages/hdf/package.py
+     var/spack/repos/spack_repo/builtin/packages/netcdf/package.py
    =======================================================
    Flake8 checks were clean.
 
@@ -236,9 +236,9 @@ However, if you aren't compliant with PEP 8, flake8 will complain:
 
 .. code-block:: console
 
-   var/spack/repos/builtin/packages/netcdf/package.py:26: [F401] 'os' imported but unused
-   var/spack/repos/builtin/packages/netcdf/package.py:61: [E303] too many blank lines (2)
-   var/spack/repos/builtin/packages/netcdf/package.py:106: [E501] line too long (92 > 79 characters)
+   var/spack/repos/spack_repo/builtin/packages/netcdf/package.py:26: [F401] 'os' imported but unused
+   var/spack/repos/spack_repo/builtin/packages/netcdf/package.py:61: [E303] too many blank lines (2)
+   var/spack/repos/spack_repo/builtin/packages/netcdf/package.py:106: [E501] line too long (92 > 79 characters)
    Flake8 found errors.
 
 Most of the error messages are straightforward, but if you don't understand what
@@ -280,7 +280,7 @@ All of these can be installed with Spack, e.g.
 
 .. warning::
 
-   Sphinx has `several required dependencies <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/py-sphinx/package.py>`_.
+   Sphinx has `several required dependencies <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/py-sphinx/package.py>`_.
    If you're using a ``python`` from Spack and you installed
    ``py-sphinx`` and friends, you need to make them available to your
    ``python``. The easiest way to do this is to run:

lib/spack/docs/developer_guide.rst

@@ -154,9 +154,7 @@ Package-related modules
 
 :mod:`spack.util.naming`
   Contains functions for mapping between Spack package names,
-  Python module names, and Python class names. Functions like
-  :func:`~spack.util.naming.mod_to_class` handle mapping package
-  module names to class names.
+  Python module names, and Python class names.
 
 :mod:`spack.directives`
   *Directives* are functions that can be called inside a package definition

lib/spack/docs/features.rst

@@ -131,7 +131,7 @@ creates a simple python file:
 It doesn't take much python coding to get from there to a working
 package:
 
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/libelf/package.py
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/libelf/package.py
    :lines: 5-
 
 Spack also provides wrapper functions around common commands like

lib/spack/docs/packaging_guide.rst

@@ -369,9 +369,9 @@ If you have a collection of software expected to work well together with
 no source code of its own, you can create a :ref:`BundlePackage <bundlepackage>`.
 Examples where bundle packages can be useful include defining suites of
 applications (e.g, `EcpProxyApps
-<https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/ecp-proxy-apps/package.py>`_), commonly used libraries
-(e.g., `AmdAocl <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/amd-aocl/package.py>`_),
-and software development kits (e.g., `EcpDataVisSdk <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/ecp-data-vis-sdk/package.py>`_).
+<https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/ecp_proxy_apps/package.py>`_), commonly used libraries
+(e.g., `AmdAocl <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/amd_aocl/package.py>`_),
+and software development kits (e.g., `EcpDataVisSdk <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/ecp_data_vis_sdk/package.py>`_).
 
 These versioned packages primarily consist of dependencies on the associated
 software packages. They can include :ref:`variants <variants>` to ensure
@@ -443,7 +443,7 @@ lives in:
 .. code-block:: console
 
    $ spack location -p gmp
-   ${SPACK_ROOT}/var/spack/repos/builtin/packages/gmp/package.py
+   ${SPACK_ROOT}/var/spack/repos/spack_repo/builtin/packages/gmp/package.py
 
 but ``spack edit`` provides a much simpler shortcut and saves you the
 trouble of typing the full path.
@@ -457,19 +457,19 @@ live in Spack's directory structure.  In general, :ref:`cmd-spack-create`
 handles creating package files for you, so you can skip most of the
 details here.
 
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-``var/spack/repos/builtin/packages``
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+``var/spack/repos/spack_repo/builtin/packages``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 A Spack installation directory is structured like a standard UNIX
 install prefix (``bin``, ``lib``, ``include``, ``var``, ``opt``,
 etc.).  Most of the code for Spack lives in ``$SPACK_ROOT/lib/spack``.
-Packages themselves live in ``$SPACK_ROOT/var/spack/repos/builtin/packages``.
+Packages themselves live in ``$SPACK_ROOT/var/spack/repos/spack_repo/builtin/packages``.
 
 If you ``cd`` to that directory, you will see directories for each
 package:
 
-.. command-output:: cd $SPACK_ROOT/var/spack/repos/builtin/packages && ls
+.. command-output:: cd $SPACK_ROOT/var/spack/repos/spack_repo/builtin/packages && ls
    :shell:
    :ellipsis: 10
 
@@ -479,7 +479,7 @@ package lives in:
 
 .. code-block:: none
 
-   $SPACK_ROOT/var/spack/repos/builtin/packages/libelf/package.py
+   $SPACK_ROOT/var/spack/repos/spack_repo/builtin/packages/libelf/package.py
 
 Alongside the ``package.py`` file, a package may contain extra
 directories or files (like patches) that it needs to build.
@@ -492,7 +492,7 @@ Packages are named after the directory containing ``package.py``. So,
 ``libelf``'s ``package.py`` lives in a directory called ``libelf``.
 The ``package.py`` file defines a class called ``Libelf``, which
 extends Spack's ``Package`` class.  For example, here is
-``$SPACK_ROOT/var/spack/repos/builtin/packages/libelf/package.py``:
+``$SPACK_ROOT/var/spack/repos/spack_repo/builtin/packages/libelf/package.py``:
 
 .. code-block:: python
    :linenos:
@@ -520,7 +520,7 @@ these:
    $ spack install libelf@0.8.13
 
 Spack sees the package name in the spec and looks for
-``libelf/package.py`` in ``var/spack/repos/builtin/packages``.
+``libelf/package.py`` in ``var/spack/repos/spack_repo/builtin/packages``.
 Likewise, if you run ``spack install py-numpy``, Spack looks for
 ``py-numpy/package.py``.
 
@@ -686,7 +686,7 @@ https://www.open-mpi.org/software/ompi/v2.1/downloads/openmpi-2.1.1.tar.bz2
 In order to handle this, you can define a ``url_for_version()`` function
 like so:
 
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/openmpi/package.py
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/openmpi/package.py
    :pyobject: Openmpi.url_for_version
 
 With the use of this ``url_for_version()``, Spack knows to download OpenMPI ``2.1.1``
@@ -787,7 +787,7 @@ of GNU. For that, Spack goes a step further and defines a mixin class that
 takes care of all of the plumbing and requires packagers to just define a proper
 ``gnu_mirror_path`` attribute:
 
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/autoconf/package.py
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/autoconf/package.py
    :lines: 9-18
 
 ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -1995,7 +1995,7 @@ structure like this:
 
 .. code-block:: none
 
-   $SPACK_ROOT/var/spack/repos/builtin/packages/
+   $SPACK_ROOT/var/spack/repos/spack_repo/builtin/packages/
        mvapich2/
            package.py
            ad_lustre_rwcontig_open_source.patch
@@ -2133,7 +2133,7 @@ handles ``RPATH``:
 
 .. _pyside-patch:
 
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/py-pyside/package.py
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/py_pyside/package.py
    :pyobject: PyPyside.patch
    :linenos:
 
@@ -2201,7 +2201,7 @@ using the ``spack resource show`` command::
 
   $ spack resource show 3877ab54
   3877ab548f88597ab2327a2230ee048d2d07ace1062efe81fc92e91b7f39cd00
-      path:       /home/spackuser/src/spack/var/spack/repos/builtin/packages/m4/gnulib-pgi.patch
+      path:       /home/spackuser/src/spack/var/spack/repos/spack_repo/builtin/packages/m4/gnulib-pgi.patch
       applies to: builtin.m4
 
 ``spack resource show`` looks up downloadable resources from package
@@ -2219,7 +2219,7 @@ wonder where the extra boost patches are coming from::
           ^boost@1.68.0%apple-clang@9.0.0+atomic+chrono~clanglibcpp cxxstd=default +date_time~debug+exception+filesystem+graph~icu+iostreams+locale+log+math~mpi+multithreaded~numpy patches=2ab6c72d03dec6a4ae20220a9dfd5c8c572c5294252155b85c6874d97c323199,b37164268f34f7133cbc9a4066ae98fda08adf51e1172223f6a969909216870f ~pic+program_options~python+random+regex+serialization+shared+signals~singlethreaded+system~taggedlayout+test+thread+timer~versionedlayout+wave arch=darwin-highsierra-x86_64
   $ spack resource show b37164268
   b37164268f34f7133cbc9a4066ae98fda08adf51e1172223f6a969909216870f
-      path:       /home/spackuser/src/spack/var/spack/repos/builtin/packages/dealii/boost_1.68.0.patch
+      path:       /home/spackuser/src/spack/var/spack/repos/spack_repo/builtin/packages/dealii/boost_1.68.0.patch
       applies to: builtin.boost
       patched by: builtin.dealii
 
@@ -2930,7 +2930,7 @@ this, Spack provides four different methods that can be overridden in a package:
 
 The Qt package, for instance, uses this call:
 
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/qt/package.py
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/qt/package.py
    :pyobject: Qt.setup_dependent_build_environment
    :linenos:
 
@@ -2958,7 +2958,7 @@ 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
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/python/package.py
    :pyobject: Python.setup_dependent_package
    :linenos:
 
@@ -3785,7 +3785,7 @@ It is usually sufficient for a packager to override a few
 build system specific helper methods or attributes to provide, for instance,
 configure arguments:
 
-.. literalinclude::  _spack_root/var/spack/repos/builtin/packages/m4/package.py
+.. literalinclude::  _spack_root/var/spack/repos/spack_repo/builtin/packages/m4/package.py
     :pyobject: M4.configure_args
     :linenos:
 
@@ -4110,7 +4110,7 @@ Shell command functions
 
 Recall the install method from ``libelf``:
 
-.. literalinclude::  _spack_root/var/spack/repos/builtin/packages/libelf/package.py
+.. literalinclude::  _spack_root/var/spack/repos/spack_repo/builtin/packages/libelf/package.py
    :pyobject: Libelf.install
    :linenos:
 
@@ -4901,7 +4901,7 @@ the one passed to install, only the MPI implementations all set some
 additional properties on it to help you out.  E.g., in openmpi, you'll
 find this:
 
-.. literalinclude:: _spack_root/var/spack/repos/builtin/packages/openmpi/package.py
+.. literalinclude:: _spack_root/var/spack/repos/spack_repo/builtin/packages/openmpi/package.py
    :pyobject: Openmpi.setup_dependent_package
 
 That code allows the ``openmpi`` package to associate an ``mpicc`` property
@@ -6001,16 +6001,16 @@ with those implemented in the package itself.
    * - Parent/Provider Package
      - Stand-alone Tests
    * - `C
-       <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/c>`_
+       <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/c>`_
      - Compiles ``hello.c`` and runs it
    * - `Cxx
-       <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/cxx>`_
+       <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/cxx>`_
      - Compiles and runs several ``hello`` programs
    * - `Fortran
-       <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/fortran>`_
+       <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/fortran>`_
      - Compiles and runs ``hello`` programs (``F`` and ``f90``)
    * - `Mpi
-       <https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/mpi>`_
+       <https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/mpi>`_
      - Compiles and runs ``mpi_hello`` (``c``, ``fortran``)
    * - :ref:`PythonPackage <pythonpackage>`
      - Imports modules listed in the ``self.import_modules`` property with defaults derived from the tarball
@@ -6031,7 +6031,7 @@ maintainers provide additional stand-alone tests customized to the package.
 One example of a package that adds its own stand-alone tests to those
 "inherited" by the virtual package it provides an implementation for is
 the `Openmpi package
-<https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/openmpi/package.py>`_.
+<https://github.com/spack/spack/blob/develop/var/spack/repos/spack_repo/builtin/packages/openmpi/package.py>`_.
 
 Below are snippets from running and viewing the stand-alone test results
 for ``openmpi``:

lib/spack/docs/repositories.rst

@@ -9,7 +9,7 @@ Package Repositories (repos.yaml)
 =================================
 
 Spack comes with thousands of built-in package recipes in
-``var/spack/repos/builtin/``.  This is a **package repository** -- a
+``var/spack/repos/spack_repo/builtin/``.  This is a **package repository** -- a
 directory that Spack searches when it needs to find a package by name.
 You may need to maintain packages for restricted, proprietary or
 experimental software separately from the built-in repository. Spack
@@ -69,7 +69,7 @@ The default ``etc/spack/defaults/repos.yaml`` file looks like this:
 .. code-block:: yaml
 
   repos:
-  - $spack/var/spack/repos/builtin
+  - $spack/var/spack/repos/spack_repo/builtin
 
 The file starts with ``repos:`` and contains a single ordered list of
 paths to repositories. Each path is on a separate line starting with
@@ -78,16 +78,16 @@ paths to repositories. Each path is on a separate line starting with
 .. code-block:: yaml
 
   repos:
-  - /opt/local-repo
-  - $spack/var/spack/repos/builtin
+  - /opt/repos/spack_repo/local_repo
+  - $spack/var/spack/repos/spack_repo/builtin
 
 When Spack interprets a spec, e.g., ``mpich`` in ``spack install mpich``,
 it searches these repositories in order (first to last) to resolve each
 package name.  In this example, Spack will look for the following
 packages and use the first valid file:
 
-1. ``/opt/local-repo/packages/mpich/package.py``
-2. ``$spack/var/spack/repos/builtin/packages/mpich/package.py``
+1. ``/opt/repos/spack_repo/local_repo/packages/mpich/package.py``
+2. ``$spack/var/spack/repos/spack_repo/builtin/packages/mpich/package.py``
 
 .. note::
 
@@ -101,14 +101,15 @@ Namespaces
 
 Every repository in Spack has an associated **namespace** defined in its
 top-level ``repo.yaml`` file.  If you look at
-``var/spack/repos/builtin/repo.yaml`` in the built-in repository, you'll
+``var/spack/repos/spack_repo/builtin/repo.yaml`` in the built-in repository, you'll
 see that its namespace is ``builtin``:
 
 .. code-block:: console
 
-  $ cat var/spack/repos/builtin/repo.yaml
+  $ cat var/spack/repos/spack_repo/builtin/repo.yaml
   repo:
     namespace: builtin
+    api: v2.0
 
 Spack records the repository namespace of each installed package.  For
 example, if you install the ``mpich`` package from the ``builtin`` repo,
@@ -217,15 +218,15 @@ Suppose you have three repositories: the builtin Spack repo
 repo containing your own prototype packages (``proto``).  Suppose they
 contain packages as follows:
 
-  +--------------+------------------------------------+-----------------------------+
-  | Namespace    | Path to repo                       | Packages                    |
-  +==============+====================================+=============================+
-  | ``proto``    | ``~/proto``                        | ``mpich``                   |
-  +--------------+------------------------------------+-----------------------------+
-  | ``llnl``     | ``/usr/local/llnl``                | ``hdf5``                    |
-  +--------------+------------------------------------+-----------------------------+
-  | ``builtin``  | ``$spack/var/spack/repos/builtin`` | ``mpich``, ``hdf5``, others |
-  +--------------+------------------------------------+-----------------------------+
+  +--------------+-----------------------------------------------+-----------------------------+
+  | Namespace    | Path to repo                                  | Packages                    |
+  +==============+===============================================+=============================+
+  | ``proto``    | ``~/my_spack_repos/spack_repo/proto``         | ``mpich``                   |
+  +--------------+-----------------------------------------------+-----------------------------+
+  | ``llnl``     | ``/usr/local/repos/spack_repo/llnl``          | ``hdf5``                    |
+  +--------------+-----------------------------------------------+-----------------------------+
+  | ``builtin``  | ``$spack/var/spack/repos/spack_repo/builtin`` | ``mpich``, ``hdf5``, others |
+  +--------------+-----------------------------------------------+-----------------------------+
 
 Suppose that ``hdf5`` depends on ``mpich``.  You can override the
 built-in ``hdf5`` by adding the ``llnl`` repo to ``repos.yaml``:
@@ -233,8 +234,8 @@ built-in ``hdf5`` by adding the ``llnl`` repo to ``repos.yaml``:
 .. code-block:: yaml
 
    repos:
-   - /usr/local/llnl
-   - $spack/var/spack/repos/builtin
+   - /usr/local/repos/spack_repo/llnl
+   - $spack/var/spack/repos/spack_repo/builtin
 
 ``spack install hdf5`` will install ``llnl.hdf5 ^builtin.mpich``.
 
@@ -243,9 +244,9 @@ If, instead, ``repos.yaml`` looks like this:
 .. code-block:: yaml
 
    repos:
-   - ~/proto
-   - /usr/local/llnl
-   - $spack/var/spack/repos/builtin
+   - ~/my_spack_repos/spack_repo/proto
+   - /usr/local/repos/spack_repo/llnl
+   - $spack/var/spack/repos/spack_repo/builtin
 
 ``spack install hdf5`` will install ``llnl.hdf5 ^proto.mpich``.
 
@@ -326,8 +327,8 @@ files, use ``spack repo list``.
 
   $ spack repo list
   ==> 2 package repositories.
-  myrepo     ~/myrepo
-  builtin    ~/spack/var/spack/repos/builtin
+  myrepo     v2.0    ~/my_spack_repos/spack_repo/myrepo
+  builtin    v2.0    ~/spack/var/spack/repos/spack_repo/builtin
 
 Each repository is listed with its associated namespace.  To get the raw,
 merged YAML from all configuration files, use ``spack config get repos``:
@@ -335,9 +336,9 @@ merged YAML from all configuration files, use ``spack config get repos``:
 .. code-block:: console
 
    $ spack config get repos
-   repos:srepos:
-   - ~/myrepo
-   - $spack/var/spack/repos/builtin
+   repos:
+   - ~/my_spack_repos/spack_repo/myrepo
+   - $spack/var/spack/repos/spack_repo/builtin
 
 Note that, unlike ``spack repo list``, this does not include the
 namespace, which is read from each repo's ``repo.yaml``.
@@ -351,66 +352,54 @@ yourself; you can use the ``spack repo create`` command.
 
 .. code-block:: console
 
-  $ spack repo create myrepo
+  $ spack repo create ~/my_spack_repos myrepo
   ==> Created repo with namespace 'myrepo'.
   ==> To register it with spack, run this command:
-    spack repo add ~/myrepo
+    spack repo add ~/my_spack_repos/spack_repo/myrepo
 
-  $ ls myrepo
+  $ ls ~/my_spack_repos/spack_repo/myrepo
   packages/  repo.yaml
 
-  $ cat myrepo/repo.yaml
+  $ cat ~/my_spack_repos/spack_repo/myrepo/repo.yaml
   repo:
     namespace: 'myrepo'
+    api: v2.0
 
-By default, the namespace of a new repo matches its directory's name.
-You can supply a custom namespace with a second argument, e.g.:
+Namespaces can also be nested, which can be useful if you have
+multiple package repositories for an organization. Spack will
+create the corresponding directory structure for you:
 
 .. code-block:: console
 
-  $ spack repo create myrepo llnl.comp
+  $ spack repo create ~/my_spack_repos llnl.comp
   ==> Created repo with namespace 'llnl.comp'.
   ==> To register it with spack, run this command:
-    spack repo add ~/myrepo
+    spack repo add ~/my_spack_repos/spack_repo/llnl/comp
 
-  $ cat myrepo/repo.yaml
+
+  $ cat ~/my_spack_repos/spack_repo/llnl/comp/repo.yaml
   repo:
     namespace: 'llnl.comp'
-
-You can also create repositories with custom structure with the ``-d/--subdirectory``
-argument, e.g.:
-
-.. code-block:: console
-
-  $ spack repo create -d applications myrepo apps
-  ==> Created repo with namespace 'apps'.
-  ==> To register it with Spack, run this command:
-    spack repo add ~/myrepo
-
-  $ ls myrepo
-  applications/  repo.yaml
-
-  $ cat myrepo/repo.yaml
-  repo:
-    namespace: apps
-    subdirectory: applications
+    api: v2.0
 
 ^^^^^^^^^^^^^^^^^^
 ``spack repo add``
 ^^^^^^^^^^^^^^^^^^
 
 Once your repository is created, you can register it with Spack with
-``spack repo add``:
+``spack repo add``. You nee to specify the path to the directory that
+contains the ``repo.yaml`` file.
 
 .. code-block:: console
 
-   $ spack repo add ./myrepo
+   $ spack repo add ~/my_spack_repos/spack_repo/llnl/comp
    ==> Added repo with namespace 'llnl.comp'.
 
    $ spack repo list
    ==> 2 package repositories.
-   llnl.comp    ~/myrepo
-   builtin      ~/spack/var/spack/repos/builtin
+  llnl.comp    v2.0    ~/my_spack_repos/spack_repo/llnl/comp
+  builtin      v2.0    ~/spack/var/spack/repos/spack_repo/builtin
+
 
 This simply adds the repo to your ``repos.yaml`` file.
 
@@ -432,46 +421,43 @@ By namespace:
 .. code-block:: console
 
   $ spack repo rm llnl.comp
-  ==> Removed repository ~/myrepo with namespace 'llnl.comp'.
+  ==> Removed repository ~/my_spack_repos/spack_repo/llnl/comp with namespace 'llnl.comp'.
 
   $ spack repo list
   ==> 1 package repository.
-  builtin    ~/spack/var/spack/repos/builtin
+  builtin    ~/spack/var/spack/repos/spack_repo/builtin
 
 By path:
 
 .. code-block:: console
 
-  $ spack repo rm ~/myrepo
-  ==> Removed repository ~/myrepo
+  $ spack repo rm ~/my_spack_repos/spack_repo/llnl/comp
+  ==> Removed repository ~/my_spack_repos/spack_repo/llnl/comp
 
   $ spack repo list
   ==> 1 package repository.
-  builtin    ~/spack/var/spack/repos/builtin
+  builtin    ~/spack/var/spack/repos/spack_repo/builtin
 
 --------------------------------
 Repo namespaces and Python
 --------------------------------
 
-You may have noticed that namespace notation for repositories is similar
-to the notation for namespaces in Python.  As it turns out, you *can*
-treat Spack repositories like Python packages; this is how they are
-implemented.
+Package repositories are implemented as Python packages. To be precise,
+they are `namespace packages
+<https://packaging.python.org/en/latest/guides/packaging-namespace-packages/>`_
+with ``spack_repo`` the top-level namespace, followed by the repository
+namespace as submodules. For example, the builtin repository corresponds
+to the Python module ``spack_repo.builtin.packages``.
 
-You could, for example, extend a ``builtin`` package in your own
+This structure allows you to extend a ``builtin`` package in your own
 repository:
 
 .. code-block:: python
 
-   from spack.pkg.builtin.mpich import Mpich
+   from spack_repo.builtin.packages.mpich.package import Mpich
 
    class MyPackage(Mpich):
        ...
 
-Spack repo namespaces are actually Python namespaces tacked on under
-``spack.pkg``.  The search semantics of ``repos.yaml`` are actually
-implemented using Python's built-in `sys.path
-<https://docs.python.org/2/library/sys.html#sys.path>`_ search.  The
-:py:mod:`spack.repo` module implements a custom `Python importer
-<https://docs.python.org/2/library/imp.html>`_.
-
+Spack populates ``sys.path`` at runtime with the path to the root of your
+package repository's ``spack_repo`` directory.

lib/spack/llnl/util/lang.py

@@ -21,6 +21,7 @@
     Dict,
     Generic,
     Iterable,
+    Iterator,
     List,
     Mapping,
     Optional,
@@ -436,46 +437,39 @@ def add_func_to_class(name, func):
     return cls
 
 
+K = TypeVar("K")
+V = TypeVar("V")
+
+
 @lazy_lexicographic_ordering
-class HashableMap(collections.abc.MutableMapping):
+class HashableMap(typing.MutableMapping[K, V]):
     """This is a hashable, comparable dictionary.  Hash is performed on
     a tuple of the values in the dictionary."""
 
     __slots__ = ("dict",)
 
     def __init__(self):
-        self.dict = {}
+        self.dict: Dict[K, V] = {}
 
-    def __getitem__(self, key):
+    def __getitem__(self, key: K) -> V:
         return self.dict[key]
 
-    def __setitem__(self, key, value):
+    def __setitem__(self, key: K, value: V) -> None:
         self.dict[key] = value
 
-    def __iter__(self):
+    def __iter__(self) -> Iterator[K]:
         return iter(self.dict)
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self.dict)
 
-    def __delitem__(self, key):
+    def __delitem__(self, key: K) -> None:
         del self.dict[key]
 
     def _cmp_iter(self):
         for _, v in sorted(self.items()):
             yield v
 
-    def copy(self):
-        """Type-agnostic clone method.  Preserves subclass type."""
-        # Construct a new dict of my type
-        self_type = type(self)
-        clone = self_type()
-
-        # Copy everything from this dict into it.
-        for key in self:
-            clone[key] = self[key].copy()
-        return clone
-
 
 def match_predicate(*args):
     """Utility function for making string matching predicates.

lib/spack/spack/__init__.py

@@ -18,7 +18,7 @@
 #: version is incremented when the package API is extended in a backwards-compatible way. The major
 #: version is incremented upon breaking changes. This version is changed independently from the
 #: Spack version.
-package_api_version = (1, 0)
+package_api_version = (2, 0)
 
 #: The minimum Package API version that this version of Spack is compatible with. This should
 #: always be a tuple of the form ``(major, 0)``, since compatibility with vX.Y implies

lib/spack/spack/build_systems/intel.py

@@ -1055,8 +1055,8 @@ def setup_dependent_build_environment(
     ) -> None:
         # NB: This function is overwritten by 'mpi' provider packages:
         #
-        # var/spack/repos/builtin/packages/intel-mpi/package.py
-        # var/spack/repos/builtin/packages/intel-parallel-studio/package.py
+        # var/spack/repos/spack_repo/builtin/packages/intel_mpi/package.py
+        # var/spack/repos/spack_repo/builtin/packages/intel_parallel_studio/package.py
         #
         # They call _setup_dependent_env_callback() as well, but with the
         # dictionary kwarg compilers_of_client{} present and populated.

lib/spack/spack/build_systems/r.py

@@ -1,22 +1,12 @@
 # Copyright Spack Project Developers. See COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-import re
-from typing import Dict, Generator, Optional, Set, Tuple, Union
+from typing import Optional, Tuple
 
-import llnl.util.filesystem as fs
-import llnl.util.lang as lang
-import llnl.util.tty as tty
 from llnl.util.filesystem import mkdirp
 from llnl.util.lang import ClassProperty, classproperty
 
-import spack.builder
-import spack.deptypes as dt
-import spack.phase_callbacks
-from spack.dependency import Dependency
 from spack.directives import extends
-from spack.error import SpackError
-from spack.spec import Spec
 
 from .generic import GenericBuilder, Package
 
@@ -44,169 +34,6 @@ def configure_vars(self):
         """Arguments to pass to install via ``--configure-vars``."""
         return []
 
-    @staticmethod
-    def parse_description(data: str) -> Generator:
-        """Parses CRAN package metadata from
-        https://cran.r-project.org/src/contrib/PACKAGES
-        and returns the list of dictionaries.
-
-        Args:
-            data (str): raw text from the package list
-
-        Returns:
-            (Generator): each entry from packages as dictionary
-
-        Note: based on PyPI pycran v0.2.0 under Apache-2.0 license.
-        """
-        fields: Set = set()
-        package: Dict = {}
-
-        def append(field_value: Union[bytes, str]):
-            pairs = list(package.items())
-            if pairs:
-                last_field = pairs[-1][0]
-                package[last_field] += field_value
-
-        # We want to iterate over each line and accumulate
-        # keys in dictionary, once we meet the same key
-        # in our dictionary we have a single package
-        # metadata parsed so we yield and repeat again.
-        for line in data.splitlines():
-            if not line.strip():
-                continue
-
-            if ":" in line:
-                parts = line.split(":", maxsplit=1)
-                field = parts[0].strip()
-                value = str("".join(parts[1:]).strip())
-
-                if not field[0].isalpha():
-                    field = ""
-                    value = line
-
-                if field and field in fields:
-                    fields = {field}
-                    result = {**package}
-                    package = {field: value}
-                    if result:
-                        yield result
-                else:
-                    # Here we want to parse dangling lines
-                    # like the ones with long dependency
-                    # list, `R (>= 2.15.0), xtable, pbapply ... \n    and more`
-                    if field:
-                        package[field] = value.strip()
-                        fields.add(field)
-                    else:
-                        append(f" {value.strip()}")
-            else:
-                append(f" {line.strip()}")
-
-        # We also need to return the metadata for
-        # the last parsed package.
-        if package:
-            yield package
-
-    @spack.phase_callbacks.run_before("install")
-    def _verify_package(self):
-        if not self.pkg.run_tests:
-            return
-
-        # Read DESCRIPTION file with dependency information
-        r_deps = []
-        with open(fs.join_path(self.stage.source_path, "DESCRIPTION")) as file:
-            for desc in RBuilder.parse_description(file.read()):
-                for field in [f for f in ["Depends", "Imports", "LinkingTo"] if f in desc]:
-                    r_deps.extend([d.strip() for d in desc[field].split(",") if d != ""])
-        tty.debug(f"DESCRIPTION: {r_deps}")
-
-        # Convert to spack dependencies format for comparison
-        deps = {}
-        r_core = [
-            "r-compiler",
-            "r-graphics",
-            "r-grdevices",
-            "r-grid",
-            "r-methods",
-            "r-parallel",
-            "r-splines",
-            "r-stats",
-            "r-stats4",
-            "r-tcltk",
-            "r-tools",
-            "r-utils",
-        ]
-        for r_dep in r_deps:
-            p = re.search(r"^[\w_.-]+", r_dep)  # first word, incl. underscore, dot, or dash
-            v = re.search("(?<=[(]).*(?=[)])", r_dep)  # everything between parentheses
-            # require valid package
-            assert p, f"Unable to find package name in {r_dep}"
-            r_spec = f"r-{p[0].strip().lower()}" if p[0].lower() != "r" else "r"
-            r_spec = re.sub(r"\.", "-", r_spec)  # dot to dash
-            # filter R core packages
-            if r_spec in r_core:
-                r_spec = "r"
-            # allow minimum or pinned versions
-            if v:
-                v = re.sub(r">=\s([\d.-]+)", r"@\1:", v[0])  # >=
-                v = re.sub(r">\s([\d.-]+)", r"@\1.1:", v)  # >
-                v = re.sub(r"==\s([\d.-]+)", r"@\1", v)  # ==
-            else:
-                v = ""
-            # merge dependencies as they are added
-            if r_spec in deps:
-                deps[r_spec].merge(Dependency(self.pkg, Spec(r_spec + v), dt.BUILD | dt.RUN))
-            else:
-                deps[r_spec] = Dependency(self.pkg, Spec(r_spec + v), dt.BUILD | dt.RUN)
-        tty.debug(f"Converted: {deps}")
-
-        # Retrieve dependencies for current spack package and version
-        spack_dependencies = []
-        for when, dep in self.pkg.dependencies.items():
-            if self.spec.satisfies(when):
-                spack_dependencies.append(dep)
-        tty.debug(f"Spack as read: {spack_dependencies}")
-        merged_dependencies = {}
-        for dep in spack_dependencies:
-            for n, d in dep.items():
-                if n in merged_dependencies:
-                    merged_dependencies[n].merge(d)
-                else:
-                    merged_dependencies[n] = d
-        tty.debug(f"Spack merged: {merged_dependencies}")
-
-        # For each R dependency, ensure Spack dependency is at least as strong
-        missing_deps = []
-        for dep in sorted(deps.keys()):
-            if dep in list(merged_dependencies.keys()):
-                # Spack dependency must satisfy R dependency
-                if not merged_dependencies[dep].spec.satisfies(deps[dep].spec):
-                    missing_deps.append(
-                        f'    depends_on("{deps[dep].spec}",'
-                        + ' type=("build", "run"),'
-                        + f' when="@{self.pkg.version}:")'
-                    )
-                # Remove from dict
-                del merged_dependencies[dep]
-            else:
-                missing_deps.append(
-                    f'    depends_on("{deps[dep].spec}",'
-                    + ' type=("build", "run"),'
-                    + f' when="@{self.pkg.version}:")'
-                )
-        for dep in merged_dependencies:
-            if re.match("^r-.*", dep):
-                missing_deps.append(
-                    f'    #depends_on("{merged_dependencies[dep].spec}") not needed anymore'
-                )
-
-        # Raise exception
-        if len(missing_deps) > 0:
-            raise SpackError(
-                "This package requires stricter dependencies than specified:\n\n"
-                + "\n".join(missing_deps)
-            )
-
     def install(self, pkg, spec, prefix):
         """Installs an R package."""
         mkdirp(pkg.module.r_lib_dir)

lib/spack/spack/builder.py

@@ -59,7 +59,7 @@ def __call__(self, spec, prefix):
 def get_builder_class(pkg, name: str) -> Optional[Type["Builder"]]:
     """Return the builder class if a package module defines it."""
     cls = getattr(pkg.module, name, None)
-    if cls and cls.__module__.startswith(spack.repo.ROOT_PYTHON_NAMESPACE):
+    if cls and spack.repo.is_package_module(cls.__module__):
         return cls
     return None
 
@@ -121,6 +121,7 @@ def __init__(self, wrapped_pkg_object, root_builder):
                 new_cls_name,
                 bases,
                 {
+                    "__module__": package_cls.__module__,
                     "run_tests": property(lambda x: x.wrapped_package_object.run_tests),
                     "test_requires_compiler": property(
                         lambda x: x.wrapped_package_object.test_requires_compiler
@@ -129,7 +130,6 @@ def __init__(self, wrapped_pkg_object, root_builder):
                     "tester": property(lambda x: x.wrapped_package_object.tester),
                 },
             )
-            new_cls.__module__ = package_cls.__module__
             self.__class__ = new_cls
             self.__dict__.update(wrapped_pkg_object.__dict__)
 

lib/spack/spack/ci/__init__.py

@@ -150,10 +150,10 @@ def get_stack_changed(env_path, rev1="HEAD^", rev2="HEAD"):
     return False
 
 
-def compute_affected_packages(rev1="HEAD^", rev2="HEAD"):
+def compute_affected_packages(rev1: str = "HEAD^", rev2: str = "HEAD") -> Set[str]:
     """Determine which packages were added, removed or changed
     between rev1 and rev2, and return the names as a set"""
-    return spack.repo.get_all_package_diffs("ARC", rev1=rev1, rev2=rev2)
+    return spack.repo.get_all_package_diffs("ARC", spack.repo.builtin_repo(), rev1=rev1, rev2=rev2)
 
 
 def get_spec_filter_list(env, affected_pkgs, dependent_traverse_depth=None):

lib/spack/spack/cmd/__init__.py

@@ -4,12 +4,14 @@
 
 import argparse
 import difflib
+import functools
 import importlib
 import os
 import re
+import subprocess
 import sys
 from collections import Counter
-from typing import List, Optional, Union
+from typing import Callable, List, Optional, Union
 
 import llnl.string
 import llnl.util.tty as tty
@@ -30,6 +32,7 @@
 import spack.store
 import spack.traverse as traverse
 import spack.user_environment as uenv
+import spack.util.executable as exe
 import spack.util.spack_json as sjson
 import spack.util.spack_yaml as syaml
 
@@ -723,3 +726,123 @@ def __init__(self, cmd_name):
             long_msg += "\n  ".join(similar)
 
         super().__init__(msg, long_msg)
+
+
+def find_pager(pager_candidates: List[str]) -> Optional[List[str]]:
+    """Find a pager from spack configuration.
+
+    Arguments:
+        pager_candidates: list of candidate commands with optional arguments, e.g. "less -FXRS"
+
+    Returns:
+        Arguments, including the found command, to launch the pager, or None if not found.
+    """
+    for pager in pager_candidates:
+        # split each string in the list of pagers into args
+        argv = pager.split()
+        if not argv:
+            continue
+
+        # try to find the requested pager command
+        command, *args = argv
+        path = exe.which_string(command)
+        if not path:
+            continue
+
+        # return the execv args we need to launch this thing
+        return [command] + args
+
+    return None
+
+
+def spack_pager_candidates() -> List[str]:
+    """Get a list of pager candidates by consulting environment and config.
+
+    Order of precedence is:
+
+    1. ``SPACK_PAGER``: pager just for spack
+    2. ``PAGER``: user's preferred pager, from their environment
+    3. ``config:pager``: list of pager candidates in config
+
+    """
+    pager_candidates = []
+
+    spack_pager = os.environ.get("SPACK_PAGER")
+    if spack_pager:
+        pager_candidates.append(spack_pager)
+
+    pager = os.environ.get("PAGER")
+    if pager:
+        pager_candidates.append(pager)
+
+    config_pagers = spack.config.get("config:pager")
+    if config_pagers:
+        pager_candidates.extend(config_pagers)
+
+    return pager_candidates
+
+
+def paged(command_function: Callable) -> Callable:
+    """Decorator for commands whose output should be sent to a pager by default.
+
+    This will launch a subprocess for, e.g., ``less``, and will redirect ``stdout`` to it, as
+    ``git`` does for commands like ``git log``.
+
+    The command will attempt to maintain colored output while paging, so you need a pager
+    that supports color, like ``less -R``. Spack defaults to using ``less -FXRS`` if it's
+    found, and nothing if not. You probably *do not* want to use ``more`` or any other
+    non-color-capable pager.
+    """
+    pager_execv_args = find_pager(spack_pager_candidates())
+    if not pager_execv_args:
+        return command_function
+
+    @functools.wraps(command_function)
+    def wrapper(*args, **kwargs):
+        # figure out if we're running the command with --help
+        is_help = False
+        if args and isinstance(args[-1], argparse.Namespace):
+            is_help = args[-1].help
+
+        # don't page if not a tty, and don't page help output
+        if not sys.stdout.isatty() or is_help:
+            return command_function(*args, **kwargs)
+
+        # Flush any buffered output before redirection.
+        sys.stdout.flush()
+
+        # save original stdout and original color setting
+        original_stdout_fd = os.dup(sys.stdout.fileno())
+        original_stdout_isatty = sys.stdout.isatty
+
+        # launch the pager
+        proc = subprocess.Popen(pager_execv_args, stdin=subprocess.PIPE)
+
+        try:
+            # Redirect stdout's file descriptor to the pager's stdin.
+            os.dup2(proc.stdin.fileno(), sys.stdout.fileno())
+
+            # make spack think the pager is a tty
+            sys.stdout.isatty = lambda: True
+
+            # run the decorated function
+            result = command_function(*args, **kwargs)
+
+            # Flush any remaining output.
+            sys.stdout.flush()
+
+            return result
+
+        finally:
+            # quit cheating on isatty
+            sys.stdout.isatty = original_stdout_isatty
+
+            # restore stdout
+            os.dup2(original_stdout_fd, sys.stdout.fileno())
+            os.close(original_stdout_fd)
+
+            # Close the pager's stdin and wait for it to finish.
+            proc.stdin.close()
+            proc.wait()
+
+    return wrapper

lib/spack/spack/cmd/ci.py

@@ -791,7 +791,9 @@ def ci_verify_versions(args):
     """
     # Get a list of all packages that have been changed or added
     # between from_ref and to_ref
-    pkgs = spack.repo.get_all_package_diffs("AC", args.from_ref, args.to_ref)
+    pkgs = spack.repo.get_all_package_diffs(
+        "AC", spack.repo.builtin_repo(), args.from_ref, args.to_ref
+    )
 
     failed_version = False
     for pkg_name in pkgs:

lib/spack/spack/cmd/config.py

@@ -10,6 +10,7 @@
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 
+import spack.cmd
 import spack.config
 import spack.environment as ev
 import spack.error
@@ -169,6 +170,7 @@ def print_flattened_configuration(*, blame: bool) -> None:
     syaml.dump_config(flattened, stream=sys.stdout, default_flow_style=False, blame=blame)
 
 
+@spack.cmd.paged
 def config_get(args):
     """Dump merged YAML configuration for a specific section.
 
@@ -178,6 +180,7 @@ def config_get(args):
     print_configuration(args, blame=False)
 
 
+@spack.cmd.paged
 def config_blame(args):
     """Print out line-by-line blame of merged YAML."""
     print_configuration(args, blame=True)

lib/spack/spack/cmd/create.py

@@ -23,7 +23,7 @@
 from spack.util.editor import editor
 from spack.util.executable import which
 from spack.util.format import get_version_lines
-from spack.util.naming import mod_to_class, simplify_name, valid_fully_qualified_module_name
+from spack.util.naming import pkg_name_to_class_name, simplify_name
 
 description = "create a new package file"
 section = "packaging"
@@ -95,7 +95,7 @@ class BundlePackageTemplate:
 
     def __init__(self, name: str, versions, languages: List[str]):
         self.name = name
-        self.class_name = mod_to_class(name)
+        self.class_name = pkg_name_to_class_name(name)
         self.versions = versions
         self.languages = languages
 
@@ -874,7 +874,7 @@ def get_name(name, url):
 
     result = simplify_name(result)
 
-    if not valid_fully_qualified_module_name(result):
+    if not re.match(r"^[a-z0-9-]+$", result):
         tty.die("Package name can only contain a-z, 0-9, and '-'")
 
     return result

lib/spack/spack/cmd/find.py

@@ -363,6 +363,7 @@ def _find_query(args, env):
     return results, concretized_but_not_installed
 
 
+@cmd.paged
 def find(parser, args):
     env = ev.active_environment()
 

lib/spack/spack/cmd/info.py

@@ -11,6 +11,7 @@
 from llnl.util.tty.colify import colify
 
 import spack.builder
+import spack.cmd
 import spack.deptypes as dt
 import spack.fetch_strategy as fs
 import spack.install_test
@@ -481,6 +482,7 @@ def print_licenses(pkg, args):
             color.cprint(line)
 
 
+@spack.cmd.paged
 def info(parser, args):
     spec = spack.spec.Spec(args.package)
     pkg_cls = spack.repo.PATH.get_pkg_class(spec.fullname)

lib/spack/spack/cmd/list.py

@@ -10,11 +10,14 @@
 import re
 import sys
 from html import escape
+from typing import Type
 
 import llnl.util.tty as tty
 from llnl.util.tty.colify import colify
 
+import spack.cmd
 import spack.deptypes as dt
+import spack.package_base
 import spack.repo
 from spack.cmd.common import arguments
 from spack.version import VersionList
@@ -139,10 +142,10 @@ def name_only(pkgs, out):
         tty.msg("%d packages" % len(pkgs))
 
 
-def github_url(pkg):
+def github_url(pkg: Type[spack.package_base.PackageBase]) -> str:
     """Link to a package file on github."""
-    url = "https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/{0}/package.py"
-    return url.format(pkg.name)
+    mod_path = pkg.__module__.replace(".", "/")
+    return f"https://github.com/spack/spack/blob/develop/var/spack/{mod_path}.py"
 
 
 def rows_for_ncols(elts, ncols):
@@ -313,6 +316,7 @@ def head(n, span_id, title, anchor=None):
         out.write("</div>\n")
 
 
+@spack.cmd.paged
 def list(parser, args):
     # retrieve the formatter to use from args
     formatter = formatters[args.format]

lib/spack/spack/cmd/pkg.py

@@ -89,17 +89,17 @@ def setup_parser(subparser):
 
 def pkg_add(args):
     """add a package to the git stage with `git add`"""
-    spack.repo.add_package_to_git_stage(args.packages)
+    spack.repo.add_package_to_git_stage(args.packages, spack.repo.builtin_repo())
 
 
 def pkg_list(args):
     """list packages associated with a particular spack git revision"""
-    colify(spack.repo.list_packages(args.rev))
+    colify(spack.repo.list_packages(args.rev, spack.repo.builtin_repo()))
 
 
 def pkg_diff(args):
     """compare packages available in two different git revisions"""
-    u1, u2 = spack.repo.diff_packages(args.rev1, args.rev2)
+    u1, u2 = spack.repo.diff_packages(args.rev1, args.rev2, spack.repo.builtin_repo())
 
     if u1:
         print("%s:" % args.rev1)
@@ -114,21 +114,23 @@ def pkg_diff(args):
 
 def pkg_removed(args):
     """show packages removed since a commit"""
-    u1, u2 = spack.repo.diff_packages(args.rev1, args.rev2)
+    u1, u2 = spack.repo.diff_packages(args.rev1, args.rev2, spack.repo.builtin_repo())
     if u1:
         colify(sorted(u1))
 
 
 def pkg_added(args):
     """show packages added since a commit"""
-    u1, u2 = spack.repo.diff_packages(args.rev1, args.rev2)
+    u1, u2 = spack.repo.diff_packages(args.rev1, args.rev2, spack.repo.builtin_repo())
     if u2:
         colify(sorted(u2))
 
 
 def pkg_changed(args):
     """show packages changed since a commit"""
-    packages = spack.repo.get_all_package_diffs(args.type, args.rev1, args.rev2)
+    packages = spack.repo.get_all_package_diffs(
+        args.type, spack.repo.builtin_repo(), args.rev1, args.rev2
+    )
 
     if packages:
         colify(sorted(packages))

lib/spack/spack/cmd/repo.py

@@ -4,6 +4,7 @@
 
 import os
 import sys
+from typing import List
 
 import llnl.util.tty as tty
 
@@ -24,9 +25,7 @@ def setup_parser(subparser):
     create_parser = sp.add_parser("create", help=repo_create.__doc__)
     create_parser.add_argument("directory", help="directory to create the repo in")
     create_parser.add_argument(
-        "namespace",
-        help="namespace to identify packages in the repository (defaults to the directory name)",
-        nargs="?",
+        "namespace", help="name or namespace to identify packages in the repository"
     )
     create_parser.add_argument(
         "-d",
@@ -138,7 +137,7 @@ def repo_remove(args):
 def repo_list(args):
     """show registered repositories and their namespaces"""
     roots = spack.config.get("repos", scope=args.scope)
-    repos = []
+    repos: List[spack.repo.Repo] = []
     for r in roots:
         try:
             repos.append(spack.repo.from_path(r))
@@ -146,17 +145,14 @@ def repo_list(args):
             continue
 
     if sys.stdout.isatty():
-        msg = "%d package repositor" % len(repos)
-        msg += "y." if len(repos) == 1 else "ies."
-        tty.msg(msg)
+        tty.msg(f"{len(repos)} package repositor" + ("y." if len(repos) == 1 else "ies."))
 
     if not repos:
         return
 
     max_ns_len = max(len(r.namespace) for r in repos)
     for repo in repos:
-        fmt = "%%-%ds%%s" % (max_ns_len + 4)
-        print(fmt % (repo.namespace, repo.root))
+        print(f"{repo.namespace:<{max_ns_len + 4}}{repo.package_api_str:<8}{repo.root}")
 
 
 def repo(parser, args):

lib/spack/spack/cmd/solve.py

@@ -136,20 +136,7 @@ def solve(parser, args):
     setup_only = set(show) == {"asp"}
     unify = spack.config.get("concretizer:unify")
     allow_deprecated = spack.config.get("config:deprecated", False)
-    if unify != "when_possible":
-        # set up solver parameters
-        # Note: reuse and other concretizer prefs are passed as configuration
-        result = solver.solve(
-            specs,
-            out=output,
-            timers=args.timers,
-            stats=args.stats,
-            setup_only=setup_only,
-            allow_deprecated=allow_deprecated,
-        )
-        if not setup_only:
-            _process_result(result, show, required_format, kwargs)
-    else:
+    if unify == "when_possible":
         for idx, result in enumerate(
             solver.solve_in_rounds(
                 specs,
@@ -166,3 +153,29 @@ def solve(parser, args):
                 print("% END ROUND {0}\n".format(idx))
             if not setup_only:
                 _process_result(result, show, required_format, kwargs)
+    elif unify:
+        # set up solver parameters
+        # Note: reuse and other concretizer prefs are passed as configuration
+        result = solver.solve(
+            specs,
+            out=output,
+            timers=args.timers,
+            stats=args.stats,
+            setup_only=setup_only,
+            allow_deprecated=allow_deprecated,
+        )
+        if not setup_only:
+            _process_result(result, show, required_format, kwargs)
+    else:
+        for spec in specs:
+            tty.msg("SOLVING SPEC:", spec)
+            result = solver.solve(
+                [spec],
+                out=output,
+                timers=args.timers,
+                stats=args.stats,
+                setup_only=setup_only,
+                allow_deprecated=allow_deprecated,
+            )
+            if not setup_only:
+                _process_result(result, show, required_format, kwargs)

lib/spack/spack/cmd/style.py

@@ -59,7 +59,7 @@ def is_package(f):
     packages, since we allow `from spack import *` and poking globals
     into packages.
     """
-    return f.startswith("var/spack/repos/") and f.endswith("package.py")
+    return f.startswith("var/spack/") and f.endswith("package.py")
 
 
 #: decorator for adding tools to the list
@@ -380,7 +380,7 @@ def run_black(black_cmd, file_list, args):
 def _module_part(root: str, expr: str):
     parts = expr.split(".")
     # spack.pkg is for repositories, don't try to resolve it here.
-    if ".".join(parts[:2]) == spack.repo.ROOT_PYTHON_NAMESPACE:
+    if expr.startswith(spack.repo.PKG_MODULE_PREFIX_V1) or expr == "spack.pkg":
         return None
     while parts:
         f1 = os.path.join(root, "lib", "spack", *parts) + ".py"

lib/spack/spack/directives_meta.py

@@ -65,7 +65,7 @@ def __init__(cls: "DirectiveMeta", name: str, bases: tuple, attr_dict: dict):
         # The instance is being initialized: if it is a package we must ensure
         # that the directives are called to set it up.
 
-        if cls.__module__.startswith(spack.repo.ROOT_PYTHON_NAMESPACE):
+        if spack.repo.is_package_module(cls.__module__):
             # Ensure the presence of the dictionaries associated with the directives.
             # All dictionaries are defaultdicts that create lists for missing keys.
             for d in DirectiveMeta._directive_dict_names:

lib/spack/spack/environment/environment.py

@@ -2312,8 +2312,12 @@ def update_environment_repository(self) -> None:
 
     def _add_to_environment_repository(self, spec_node: Spec) -> None:
         """Add the root node of the spec to the environment repository"""
-        repository_dir = os.path.join(self.repos_path, spec_node.namespace)
-        repository = spack.repo.create_or_construct(repository_dir, spec_node.namespace)
+        namespace: str = spec_node.namespace
+        repository = spack.repo.create_or_construct(
+            root=os.path.join(self.repos_path, namespace),
+            namespace=namespace,
+            package_api=spack.repo.PATH.get_repo(namespace).package_api,
+        )
         pkg_dir = repository.dirname_for_package_name(spec_node.name)
         fs.mkdirp(pkg_dir)
         spack.repo.PATH.dump_provenance(spec_node, pkg_dir)

lib/spack/spack/installer.py

@@ -566,10 +566,11 @@ def dump_packages(spec: "spack.spec.Spec", path: str) -> None:
                 tty.warn(f"Warning: Couldn't copy in provenance for {node.name}")
 
         # Create a destination repository
-        dest_repo_root = os.path.join(path, node.namespace)
-        if not os.path.exists(dest_repo_root):
-            spack.repo.create_repo(dest_repo_root)
-        repo = spack.repo.from_path(dest_repo_root)
+        pkg_api = spack.repo.PATH.get_repo(node.namespace).package_api
+        repo_root = os.path.join(path, node.namespace) if pkg_api < (2, 0) else path
+        repo = spack.repo.create_or_construct(
+            repo_root, namespace=node.namespace, package_api=pkg_api
+        )
 
         # Get the location of the package in the dest repo.
         dest_pkg_dir = repo.dirname_for_package_name(node.name)

lib/spack/spack/main.py

@@ -374,6 +374,12 @@ def make_argument_parser(**kwargs):
         choices=("always", "never", "auto"),
         help="when to colorize output (default: auto)",
     )
+    parser.add_argument(
+        "--no-pager",
+        action="store_true",
+        default=False,
+        help="do not run any output through a pager",
+    )
     parser.add_argument(
         "-c",
         "--config",
@@ -536,6 +542,10 @@ def setup_main_options(args):
     if args.timestamp:
         tty.set_timestamp(True)
 
+    # override pager configuration (note ::)
+    if args.no_pager:
+        spack.config.set("config::pager", [], scope="command_line")
+
     # override lock configuration if passed on command line
     if args.locks is not None:
         if args.locks is False:

lib/spack/spack/package_base.py

@@ -47,6 +47,7 @@
 import spack.url
 import spack.util.environment
 import spack.util.executable
+import spack.util.naming
 import spack.util.path
 import spack.util.web
 import spack.variant
@@ -838,26 +839,36 @@ def fullname(cls):
     def fullnames(cls):
         """Fullnames for this package and any packages from which it inherits."""
         fullnames = []
-        for cls in cls.__mro__:
-            namespace = getattr(cls, "namespace", None)
-            if namespace:
-                fullnames.append("%s.%s" % (namespace, cls.name))
-            if namespace == "builtin":
-                # builtin packages cannot inherit from other repos
+        for base in cls.__mro__:
+            if not spack.repo.is_package_module(base.__module__):
                 break
+            fullnames.append(base.fullname)
         return fullnames
 
     @classproperty
     def name(cls):
-        """The name of this package.
-
-        The name of a package is the name of its Python module, without
-        the containing module names.
-        """
+        """The name of this package."""
         if cls._name is None:
-            cls._name = cls.module.__name__
-            if "." in cls._name:
-                cls._name = cls._name[cls._name.rindex(".") + 1 :]
+            # We cannot know the exact package API version, but we can distinguish between v1
+            # v2 based on the module. We don't want to figure out the exact package API version
+            # since it requires parsing the repo.yaml.
+            module = cls.__module__
+
+            if module.startswith(spack.repo.PKG_MODULE_PREFIX_V1):
+                version = (1, 0)
+            elif module.startswith(spack.repo.PKG_MODULE_PREFIX_V2):
+                version = (2, 0)
+            else:
+                raise ValueError(f"Package {cls.__qualname__} is not a known Spack package")
+
+            if version < (2, 0):
+                # spack.pkg.builtin.package_name.
+                _, _, pkg_module = module.rpartition(".")
+            else:
+                # spack_repo.builtin.packages.package_name.package
+                pkg_module = module.rsplit(".", 2)[-2]
+
+            cls._name = spack.util.naming.pkg_dir_to_pkg_name(pkg_module, version)
         return cls._name
 
     @classproperty

lib/spack/spack/paths.py

@@ -56,8 +56,9 @@
 
 # read-only things in $spack/var/spack
 repos_path = os.path.join(var_path, "repos")
-packages_path = os.path.join(repos_path, "builtin")
-mock_packages_path = os.path.join(repos_path, "builtin.mock")
+test_repos_path = os.path.join(var_path, "test_repos")
+packages_path = os.path.join(repos_path, "spack_repo", "builtin")
+mock_packages_path = os.path.join(test_repos_path, "builtin.mock")
 
 #
 # Writable things in $spack/var/spack

lib/spack/spack/repo.py

@@ -47,40 +47,34 @@
 import spack.util.path
 import spack.util.spack_yaml as syaml
 
-#: Package modules are imported as spack.pkg.<repo-namespace>.<pkg-name>
-ROOT_PYTHON_NAMESPACE = "spack.pkg"
+PKG_MODULE_PREFIX_V1 = "spack.pkg."
+PKG_MODULE_PREFIX_V2 = "spack_repo."
 
 _API_REGEX = re.compile(r"^v(\d+)\.(\d+)$")
 
 
-def python_package_for_repo(namespace):
-    """Returns the full namespace of a repository, given its relative one
-
-    For instance:
-
-        python_package_for_repo('builtin') == 'spack.pkg.builtin'
-
-    Args:
-        namespace (str): repo namespace
-    """
-    return "{0}.{1}".format(ROOT_PYTHON_NAMESPACE, namespace)
+def is_package_module(fullname: str) -> bool:
+    """Check if the given module is a package module."""
+    return fullname.startswith(PKG_MODULE_PREFIX_V1) or fullname.startswith(PKG_MODULE_PREFIX_V2)
 
 
-def namespace_from_fullname(fullname):
+def namespace_from_fullname(fullname: str) -> str:
     """Return the repository namespace only for the full module name.
 
     For instance:
 
-        namespace_from_fullname('spack.pkg.builtin.hdf5') == 'builtin'
+        namespace_from_fullname("spack.pkg.builtin.hdf5") == "builtin"
+        namespace_from_fullname("spack_repo.x.y.z.packages.pkg_name.package") == "x.y.z"
 
     Args:
-        fullname (str): full name for the Python module
+        fullname: full name for the Python module
     """
-    namespace, dot, module = fullname.rpartition(".")
-    prefix_and_dot = "{0}.".format(ROOT_PYTHON_NAMESPACE)
-    if namespace.startswith(prefix_and_dot):
-        namespace = namespace[len(prefix_and_dot) :]
-    return namespace
+    if fullname.startswith(PKG_MODULE_PREFIX_V1):
+        namespace, _, _ = fullname.rpartition(".")
+        return namespace[len(PKG_MODULE_PREFIX_V1) :]
+    elif fullname.startswith(PKG_MODULE_PREFIX_V2) and fullname.endswith(".package"):
+        return ".".join(fullname.split(".")[1:-3])
+    return fullname
 
 
 class SpackNamespaceLoader:
@@ -92,14 +86,14 @@ def exec_module(self, module):
 
 
 class ReposFinder:
-    """MetaPathFinder class that loads a Python module corresponding to a Spack package.
+    """MetaPathFinder class that loads a Python module corresponding to an API v1 Spack package.
 
     Returns a loader based on the inspection of the current repository list.
     """
 
     def __init__(self):
         self._repo_init = _path
-        self._repo = None
+        self._repo: Optional[RepoType] = None
 
     @property
     def current_repository(self):
@@ -127,7 +121,7 @@ def find_spec(self, fullname, python_path, target=None):
             raise RuntimeError('cannot reload module "{0}"'.format(fullname))
 
         # Preferred API from https://peps.python.org/pep-0451/
-        if not fullname.startswith(ROOT_PYTHON_NAMESPACE):
+        if not fullname.startswith(PKG_MODULE_PREFIX_V1) and fullname != "spack.pkg":
             return None
 
         loader = self.compute_loader(fullname)
@@ -135,16 +129,17 @@ def find_spec(self, fullname, python_path, target=None):
             return None
         return importlib.util.spec_from_loader(fullname, loader)
 
-    def compute_loader(self, fullname):
+    def compute_loader(self, fullname: str):
         # namespaces are added to repo, and package modules are leaves.
         namespace, dot, module_name = fullname.rpartition(".")
 
         # If it's a module in some repo, or if it is the repo's namespace, let the repo handle it.
-        is_repo_path = isinstance(self.current_repository, RepoPath)
+        current_repo = self.current_repository
+        is_repo_path = isinstance(current_repo, RepoPath)
         if is_repo_path:
-            repos = self.current_repository.repos
+            repos = current_repo.repos
         else:
-            repos = [self.current_repository]
+            repos = [current_repo]
 
         for repo in repos:
             # We are using the namespace of the repo and the repo contains the package
@@ -161,7 +156,9 @@ def compute_loader(self, fullname):
 
         # No repo provides the namespace, but it is a valid prefix of
         # something in the RepoPath.
-        if is_repo_path and self.current_repository.by_namespace.is_prefix(fullname):
+        if is_repo_path and current_repo.by_namespace.is_prefix(
+            fullname[len(PKG_MODULE_PREFIX_V1) :]
+        ):
             return SpackNamespaceLoader()
 
         return None
@@ -179,12 +176,12 @@ def compute_loader(self, fullname):
 NOT_PROVIDED = object()
 
 
-def packages_path():
+def builtin_repo() -> "Repo":
     """Get the test repo if it is active, otherwise the builtin repo."""
     try:
-        return PATH.get_repo("builtin.mock").packages_path
+        return PATH.get_repo("builtin.mock")
     except UnknownNamespaceError:
-        return PATH.get_repo("builtin").packages_path
+        return PATH.get_repo("builtin")
 
 
 class GitExe:
@@ -192,24 +189,25 @@ class GitExe:
     # invocations.
     #
     # Not using -C as that is not supported for git < 1.8.5.
-    def __init__(self):
+    def __init__(self, packages_path: str):
         self._git_cmd = spack.util.git.git(required=True)
+        self.packages_dir = packages_path
 
-    def __call__(self, *args, **kwargs):
-        with working_dir(packages_path()):
-            return self._git_cmd(*args, **kwargs)
+    def __call__(self, *args, **kwargs) -> str:
+        with working_dir(self.packages_dir):
+            return self._git_cmd(*args, **kwargs, output=str)
 
 
-def list_packages(rev):
+def list_packages(rev: str, repo: "Repo") -> List[str]:
     """List all packages associated with the given revision"""
-    git = GitExe()
+    git = GitExe(repo.packages_path)
 
     # git ls-tree does not support ... merge-base syntax, so do it manually
     if rev.endswith("..."):
         ref = rev.replace("...", "")
-        rev = git("merge-base", ref, "HEAD", output=str).strip()
+        rev = git("merge-base", ref, "HEAD").strip()
 
-    output = git("ls-tree", "-r", "--name-only", rev, output=str)
+    output = git("ls-tree", "-r", "--name-only", rev)
 
     # recursively list the packages directory
     package_paths = [
@@ -217,54 +215,54 @@ def list_packages(rev):
     ]
 
     # take the directory names with one-level-deep package files
-    package_names = sorted(set([line[0] for line in package_paths if len(line) == 2]))
+    package_names = [
+        nm.pkg_dir_to_pkg_name(line[0], repo.package_api)
+        for line in package_paths
+        if len(line) == 2
+    ]
 
-    return package_names
+    return sorted(set(package_names))
 
 
-def diff_packages(rev1, rev2):
+def diff_packages(rev1: str, rev2: str, repo: "Repo") -> Tuple[Set[str], Set[str]]:
     """Compute packages lists for the two revisions and return a tuple
     containing all the packages in rev1 but not in rev2 and all the
     packages in rev2 but not in rev1."""
-    p1 = set(list_packages(rev1))
-    p2 = set(list_packages(rev2))
+    p1 = set(list_packages(rev1, repo))
+    p2 = set(list_packages(rev2, repo))
     return p1.difference(p2), p2.difference(p1)
 
 
-def get_all_package_diffs(type, rev1="HEAD^1", rev2="HEAD"):
-    """Show packages changed, added, or removed (or any combination of those)
-       since a commit.
+def get_all_package_diffs(type: str, repo: "Repo", rev1="HEAD^1", rev2="HEAD") -> Set[str]:
+    """Get packages changed, added, or removed (or any combination of those) since a commit.
 
     Arguments:
 
-        type (str): String containing one or more of 'A', 'R', 'C'
-        rev1 (str): Revision to compare against, default is 'HEAD^'
-        rev2 (str): Revision to compare to rev1, default is 'HEAD'
-
-    Returns:
-
-        A set contain names of affected packages.
+        type: String containing one or more of 'A', 'R', 'C'
+        rev1: Revision to compare against, default is 'HEAD^'
+        rev2: Revision to compare to rev1, default is 'HEAD'
     """
     lower_type = type.lower()
     if not re.match("^[arc]*$", lower_type):
         tty.die(
-            "Invald change type: '%s'." % type,
-            "Can contain only A (added), R (removed), or C (changed)",
+            f"Invalid change type: '{type}'. "
+            "Can contain only A (added), R (removed), or C (changed)"
         )
 
-    removed, added = diff_packages(rev1, rev2)
+    removed, added = diff_packages(rev1, rev2, repo)
 
-    git = GitExe()
-    out = git("diff", "--relative", "--name-only", rev1, rev2, output=str).strip()
+    git = GitExe(repo.packages_path)
+    out = git("diff", "--relative", "--name-only", rev1, rev2).strip()
 
     lines = [] if not out else re.split(r"\s+", out)
-    changed = set()
+    changed: Set[str] = set()
     for path in lines:
-        pkg_name, _, _ = path.partition("/")
+        dir_name, _, _ = path.partition("/")
+        pkg_name = nm.pkg_dir_to_pkg_name(dir_name, repo.package_api)
         if pkg_name not in added and pkg_name not in removed:
             changed.add(pkg_name)
 
-    packages = set()
+    packages: Set[str] = set()
     if "a" in lower_type:
         packages |= added
     if "r" in lower_type:
@@ -275,14 +273,14 @@ def get_all_package_diffs(type, rev1="HEAD^1", rev2="HEAD"):
     return packages
 
 
-def add_package_to_git_stage(packages):
+def add_package_to_git_stage(packages: List[str], repo: "Repo") -> None:
     """add a package to the git stage with `git add`"""
-    git = GitExe()
+    git = GitExe(repo.packages_path)
 
     for pkg_name in packages:
         filename = PATH.filename_for_package_name(pkg_name)
         if not os.path.isfile(filename):
-            tty.die("No such package: %s.  Path does not exist:" % pkg_name, filename)
+            tty.die(f"No such package: {pkg_name}.  Path does not exist:", filename)
 
         git("add", filename)
 
@@ -352,9 +350,10 @@ class FastPackageChecker(collections.abc.Mapping):
     #: Global cache, reused by every instance
     _paths_cache: Dict[str, Dict[str, os.stat_result]] = {}
 
-    def __init__(self, packages_path):
+    def __init__(self, packages_path: str, package_api: Tuple[int, int]):
         # The path of the repository managed by this instance
         self.packages_path = packages_path
+        self.package_api = package_api
 
         # If the cache we need is not there yet, then build it appropriately
         if packages_path not in self._paths_cache:
@@ -379,41 +378,38 @@ def _create_new_cache(self) -> Dict[str, os.stat_result]:
         # Create a dictionary that will store the mapping between a
         # package name and its stat info
         cache: Dict[str, os.stat_result] = {}
-        for pkg_name in os.listdir(self.packages_path):
-            # Skip non-directories in the package root.
-            pkg_dir = os.path.join(self.packages_path, pkg_name)
+        with os.scandir(self.packages_path) as entries:
+            for entry in entries:
+                # Construct the file name from the directory
+                pkg_file = os.path.join(entry.path, package_file_name)
 
-            # Warn about invalid names that look like packages.
-            if not nm.valid_module_name(pkg_name):
-                if not pkg_name.startswith(".") and pkg_name != "repo.yaml":
+                try:
+                    sinfo = os.stat(pkg_file)
+                except OSError as e:
+                    if e.errno in (errno.ENOENT, errno.ENOTDIR):
+                        # No package.py file here.
+                        continue
+                    elif e.errno == errno.EACCES:
+                        tty.warn(f"Can't read package file {pkg_file}.")
+                        continue
+                    raise e
+
+                # If it's not a file, skip it.
+                if not stat.S_ISREG(sinfo.st_mode):
+                    continue
+
+                # Only consider package.py files in directories that are valid module names under
+                # the current package API
+                if not nm.valid_module_name(entry.name, self.package_api):
+                    x, y = self.package_api
                     tty.warn(
-                        'Skipping package at {0}. "{1}" is not '
-                        "a valid Spack module name.".format(pkg_dir, pkg_name)
+                        f"Package {pkg_file} cannot be used because `{entry.name}` is not a valid "
+                        f"Spack package module name for Package API v{x}.{y}."
                     )
-                continue
-
-            # Construct the file name from the directory
-            pkg_file = os.path.join(self.packages_path, pkg_name, package_file_name)
-
-            # Use stat here to avoid lots of calls to the filesystem.
-            try:
-                sinfo = os.stat(pkg_file)
-            except OSError as e:
-                if e.errno == errno.ENOENT:
-                    # No package.py file here.
                     continue
-                elif e.errno == errno.EACCES:
-                    tty.warn("Can't read package file %s." % pkg_file)
-                    continue
-                raise e
 
-            # If it's not a file, skip it.
-            if stat.S_ISDIR(sinfo.st_mode):
-                continue
-
-            # If it is a file, then save the stats under the
-            # appropriate key
-            cache[pkg_name] = sinfo
+                # Store the stat info by package name.
+                cache[nm.pkg_dir_to_pkg_name(entry.name, self.package_api)] = sinfo
 
         return cache
 
@@ -688,7 +684,7 @@ def put_first(self, repo: "Repo") -> None:
             return
 
         self.repos.insert(0, repo)
-        self.by_namespace[repo.full_namespace] = repo
+        self.by_namespace[repo.namespace] = repo
 
     def put_last(self, repo):
         """Add repo last in the search path."""
@@ -700,8 +696,8 @@ def put_last(self, repo):
         self.repos.append(repo)
 
         # don't mask any higher-precedence repos with same namespace
-        if repo.full_namespace not in self.by_namespace:
-            self.by_namespace[repo.full_namespace] = repo
+        if repo.namespace not in self.by_namespace:
+            self.by_namespace[repo.namespace] = repo
 
     def remove(self, repo):
         """Remove a repo from the search path."""
@@ -710,10 +706,9 @@ def remove(self, repo):
 
     def get_repo(self, namespace: str) -> "Repo":
         """Get a repository by namespace."""
-        full_namespace = python_package_for_repo(namespace)
-        if full_namespace not in self.by_namespace:
+        if namespace not in self.by_namespace:
             raise UnknownNamespaceError(namespace)
-        return self.by_namespace[full_namespace]
+        return self.by_namespace[namespace]
 
     def first_repo(self) -> Optional["Repo"]:
         """Get the first repo in precedence order."""
@@ -821,10 +816,9 @@ def repo_for_pkg(self, spec: Union[str, "spack.spec.Spec"]) -> "Repo":
         # If the spec already has a namespace, then return the
         # corresponding repo if we know about it.
         if namespace:
-            fullspace = python_package_for_repo(namespace)
-            if fullspace not in self.by_namespace:
+            if namespace not in self.by_namespace:
                 raise UnknownNamespaceError(namespace, name=name)
-            return self.by_namespace[fullspace]
+            return self.by_namespace[namespace]
 
         # If there's no namespace, search in the RepoPath.
         for repo in self.repos:
@@ -845,8 +839,15 @@ def get(self, spec: "spack.spec.Spec") -> "spack.package_base.PackageBase":
         assert isinstance(spec, spack.spec.Spec) and spec.concrete, msg
         return self.repo_for_pkg(spec).get(spec)
 
+    def python_paths(self) -> List[str]:
+        """Return a list of all the Python paths in the repos."""
+        return [repo.python_path for repo in self.repos if repo.python_path]
+
     def get_pkg_class(self, pkg_name: str) -> Type["spack.package_base.PackageBase"]:
         """Find a class for the spec's package and return the class object."""
+        for p in self.python_paths():
+            if p not in sys.path:
+                sys.path.insert(0, p)
         return self.repo_for_pkg(pkg_name).get_pkg_class(pkg_name)
 
     @autospec
@@ -942,6 +943,30 @@ def _parse_package_api_version(
     )
 
 
+def _validate_and_normalize_subdir(subdir: Any, root: str, package_api: Tuple[int, int]) -> str:
+    if not isinstance(subdir, str):
+        raise BadRepoError(f"Invalid subdirectory '{subdir}' in '{root}'. Must be a string")
+
+    if package_api < (2, 0):
+        return subdir  # In v1.x we did not validate subdir names
+
+    if subdir in (".", ""):
+        raise BadRepoError(
+            f"Invalid subdirectory '{subdir}' in '{root}'. Use a symlink packages -> . instead"
+        )
+
+    # Otherwise we expect a directory name (not path) that can be used as a Python module.
+    if os.sep in subdir:
+        raise BadRepoError(
+            f"Invalid subdirectory '{subdir}' in '{root}'. Expected a directory name, not a path"
+        )
+    if not nm.valid_module_name(subdir, package_api):
+        raise BadRepoError(
+            f"Invalid subdirectory '{subdir}' in '{root}'. Must be a valid Python module name"
+        )
+    return subdir
+
+
 class Repo:
     """Class representing a package repository in the filesystem.
 
@@ -962,6 +987,8 @@ class Repo:
         :py:data:`spack.package_api_version`.
     """
 
+    namespace: str
+
     def __init__(
         self,
         root: str,
@@ -991,32 +1018,79 @@ def check(condition, msg):
 
         # Read configuration and validate namespace
         config = self._read_config()
+
+        self.package_api = _parse_package_api_version(config)
+        self.subdirectory = _validate_and_normalize_subdir(
+            config.get("subdirectory", packages_dir_name), root, self.package_api
+        )
+        self.packages_path = os.path.join(self.root, self.subdirectory)
+
         check(
-            "namespace" in config,
-            f"{os.path.join(root, repo_config_name)} must define a namespace.",
+            os.path.isdir(self.packages_path),
+            f"No directory '{self.subdirectory}' found in '{root}'",
         )
 
-        self.namespace: str = config["namespace"]
-        check(
-            re.match(r"[a-zA-Z][a-zA-Z0-9_.]+", self.namespace),
-            f"Invalid namespace '{self.namespace}' in repo '{self.root}'. "
-            "Namespaces must be valid python identifiers separated by '.'",
-        )
+        # The parent dir of spack_repo/ which should be added to sys.path for api v2.x
+        self.python_path: Optional[str] = None
+
+        if self.package_api < (2, 0):
+            check(
+                "namespace" in config,
+                f"{os.path.join(root, repo_config_name)} must define a namespace.",
+            )
+            self.namespace = config["namespace"]
+            # Note: for Package API v1.x the namespace validation always had bugs, which won't be
+            # fixed for compatibility reasons. The regex is missing "$" at the end, and it claims
+            # to test for valid identifiers, but fails to split on `.` first.
+            check(
+                isinstance(self.namespace, str)
+                and re.match(r"[a-zA-Z][a-zA-Z0-9_.]+", self.namespace),
+                f"Invalid namespace '{self.namespace}' in repo '{self.root}'. "
+                "Namespaces must be valid python identifiers separated by '.'",
+            )
+        else:
+            # From Package API v2.0 the namespace follows from the directory structure.
+            check(
+                f"{os.sep}spack_repo{os.sep}" in self.root,
+                f"Invalid repository path '{self.root}'. "
+                f"Path must contain 'spack_repo{os.sep}'",
+            )
+            derived_namespace = self.root.rpartition(f"spack_repo{os.sep}")[2].replace(os.sep, ".")
+            if "namespace" in config:
+                self.namespace = config["namespace"]
+
+                check(
+                    isinstance(self.namespace, str) and self.namespace == derived_namespace,
+                    f"Namespace '{self.namespace}' should be {derived_namespace} or omitted in "
+                    f"{os.path.join(root, repo_config_name)}",
+                )
+            else:
+                self.namespace = derived_namespace
+
+            # strip the namespace directories from the root path to get the python path
+            # e.g. /my/pythonpath/spack_repo/x/y/z -> /my/pythonpath
+            python_path = self.root
+            for _ in self.namespace.split("."):
+                python_path = os.path.dirname(python_path)
+            self.python_path = os.path.dirname(python_path)
+
+            # check that all subdirectories are valid module names
+            check(
+                all(nm.valid_module_name(x, self.package_api) for x in self.namespace.split(".")),
+                f"Invalid namespace '{self.namespace}' in repo '{self.root}'",
+            )
 
         # Set up 'full_namespace' to include the super-namespace
-        self.full_namespace = python_package_for_repo(self.namespace)
+        if self.package_api < (2, 0):
+            self.full_namespace = f"{PKG_MODULE_PREFIX_V1}{self.namespace}"
+        elif self.subdirectory == ".":
+            self.full_namespace = f"{PKG_MODULE_PREFIX_V2}{self.namespace}"
+        else:
+            self.full_namespace = f"{PKG_MODULE_PREFIX_V2}{self.namespace}.{self.subdirectory}"
 
         # Keep name components around for checking prefixes.
         self._names = self.full_namespace.split(".")
 
-        packages_dir: str = config.get("subdirectory", packages_dir_name)
-        self.packages_path = os.path.join(self.root, packages_dir)
-        check(
-            os.path.isdir(self.packages_path), f"No directory '{packages_dir}' found in '{root}'"
-        )
-
-        self.package_api = _parse_package_api_version(config)
-
         # Class attribute overrides by package name
         self.overrides = overrides or {}
 
@@ -1030,27 +1104,36 @@ def check(condition, msg):
         self._repo_index: Optional[RepoIndex] = None
         self._cache = cache
 
+    @property
+    def package_api_str(self) -> str:
+        return f"v{self.package_api[0]}.{self.package_api[1]}"
+
     def finder(self, value: RepoPath) -> None:
         self._finder = value
 
     def real_name(self, import_name: str) -> Optional[str]:
         """Allow users to import Spack packages using Python identifiers.
 
-        A python identifier might map to many different Spack package
-        names due to hyphen/underscore ambiguity.
+        In Package API v1.x, there was no canonical module name for a package, and package's dir
+        was not necessarily a valid Python module name. For that case we have to guess the actual
+        package directory. From Package API v2.0 there is a one-to-one mapping between Spack
+        package names and Python module names, so there is no guessing.
 
-        Easy example:
-            num3proxy   -> 3proxy
-
-        Ambiguous:
+        For Packge API v1.x we support the following one-to-many mappings:
+            num3proxy -> 3proxy
             foo_bar -> foo_bar, foo-bar
-
-        More ambiguous:
             foo_bar_baz -> foo_bar_baz, foo-bar-baz, foo_bar-baz, foo-bar_baz
         """
+        if self.package_api >= (2, 0):
+            if nm.pkg_dir_to_pkg_name(import_name, package_api=self.package_api) in self:
+                return import_name
+            return None
+
         if import_name in self:
             return import_name
 
+        # For v1 generate the possible package names from a module name, and return the first
+        # package name that exists in this repo.
         options = nm.possible_spack_module_names(import_name)
         try:
             options.remove(import_name)
@@ -1183,7 +1266,9 @@ def extensions_for(
     def dirname_for_package_name(self, pkg_name: str) -> str:
         """Given a package name, get the directory containing its package.py file."""
         _, unqualified_name = self.partition_package_name(pkg_name)
-        return os.path.join(self.packages_path, unqualified_name)
+        return os.path.join(
+            self.packages_path, nm.pkg_name_to_pkg_dir(unqualified_name, self.package_api)
+        )
 
     def filename_for_package_name(self, pkg_name: str) -> str:
         """Get the filename for the module we should load for a particular
@@ -1200,7 +1285,7 @@ def filename_for_package_name(self, pkg_name: str) -> str:
     @property
     def _pkg_checker(self) -> FastPackageChecker:
         if self._fast_package_checker is None:
-            self._fast_package_checker = FastPackageChecker(self.packages_path)
+            self._fast_package_checker = FastPackageChecker(self.packages_path, self.package_api)
         return self._fast_package_checker
 
     def all_package_names(self, include_virtuals: bool = False) -> List[str]:
@@ -1212,7 +1297,9 @@ def all_package_names(self, include_virtuals: bool = False) -> List[str]:
 
     def package_path(self, name: str) -> str:
         """Get path to package.py file for this repo."""
-        return os.path.join(self.packages_path, name, package_file_name)
+        return os.path.join(
+            self.packages_path, nm.pkg_name_to_pkg_dir(name, self.package_api), package_file_name
+        )
 
     def all_package_paths(self) -> Generator[str, None, None]:
         for name in self.all_package_names():
@@ -1270,15 +1357,19 @@ def get_pkg_class(self, pkg_name: str) -> Type["spack.package_base.PackageBase"]
         package. Then extracts the package class from the module
         according to Spack's naming convention.
         """
-        namespace, pkg_name = self.partition_package_name(pkg_name)
-        class_name = nm.mod_to_class(pkg_name)
-        fullname = f"{self.full_namespace}.{pkg_name}"
+        _, pkg_name = self.partition_package_name(pkg_name)
+        fullname = f"{self.full_namespace}.{nm.pkg_name_to_pkg_dir(pkg_name, self.package_api)}"
+        if self.package_api >= (2, 0):
+            fullname += ".package"
 
+        class_name = nm.pkg_name_to_class_name(pkg_name)
+        if self.python_path and self.python_path not in sys.path:
+            sys.path.insert(0, self.python_path)
         try:
             with REPOS_FINDER.switch_repo(self._finder or self):
                 module = importlib.import_module(fullname)
-        except ImportError:
-            raise UnknownPackageError(fullname)
+        except ImportError as e:
+            raise UnknownPackageError(fullname) from e
         except Exception as e:
             msg = f"cannot load package '{pkg_name}' from the '{self.namespace}' repository: {e}"
             raise RepoError(msg) from e
@@ -1369,46 +1460,71 @@ def partition_package_name(pkg_name: str) -> Tuple[str, str]:
     return namespace, pkg_name
 
 
-def create_repo(root, namespace=None, subdir=packages_dir_name):
+def get_repo_yaml_dir(
+    root: str, namespace: Optional[str], package_api: Tuple[int, int]
+) -> Tuple[str, str]:
+    """Returns the directory where repo.yaml is located and the effective namespace."""
+    if package_api < (2, 0):
+        namespace = namespace or os.path.basename(root)
+        # This ad-hoc regex is left for historical reasons, and should not have a breaking change.
+        if not re.match(r"\w[\.\w-]*", namespace):
+            raise InvalidNamespaceError(f"'{namespace}' is not a valid namespace.")
+        return root, namespace
+
+    # Package API v2 has <root>/spack_repo/<namespace>/<subdir> structure and requires a namespace
+    if namespace is None:
+        raise InvalidNamespaceError("Namespace must be provided.")
+
+    # if namespace has dots those translate to subdirs of further namespace packages.
+    namespace_components = namespace.split(".")
+
+    if not all(nm.valid_module_name(n, package_api=package_api) for n in namespace_components):
+        raise InvalidNamespaceError(f"'{namespace}' is not a valid namespace." % namespace)
+
+    return os.path.join(root, "spack_repo", *namespace_components), namespace
+
+
+def create_repo(
+    root,
+    namespace: Optional[str] = None,
+    subdir: str = packages_dir_name,
+    package_api: Tuple[int, int] = spack.package_api_version,
+) -> Tuple[str, str]:
     """Create a new repository in root with the specified namespace.
 
     If the namespace is not provided, use basename of root.
     Return the canonicalized path and namespace of the created repository.
     """
     root = spack.util.path.canonicalize_path(root)
-    if not namespace:
-        namespace = os.path.basename(root)
+    repo_yaml_dir, namespace = get_repo_yaml_dir(os.path.abspath(root), namespace, package_api)
 
-    if not re.match(r"\w[\.\w-]*", namespace):
-        raise InvalidNamespaceError("'%s' is not a valid namespace." % namespace)
+    existed = True
+    try:
+        dir_entry = next(os.scandir(repo_yaml_dir), None)
+    except OSError as e:
+        if e.errno == errno.ENOENT:
+            existed = False
+            dir_entry = None
+        else:
+            raise BadRepoError(f"Cannot create new repo in {root}: {e}")
 
-    existed = False
-    if os.path.exists(root):
-        if os.path.isfile(root):
-            raise BadRepoError("File %s already exists and is not a directory" % root)
-        elif os.path.isdir(root):
-            if not os.access(root, os.R_OK | os.W_OK):
-                raise BadRepoError("Cannot create new repo in %s: cannot access directory." % root)
-            if os.listdir(root):
-                raise BadRepoError("Cannot create new repo in %s: directory is not empty." % root)
-        existed = True
+    if dir_entry is not None:
+        raise BadRepoError(f"Cannot create new repo in {root}: directory is not empty.")
 
-    full_path = os.path.realpath(root)
-    parent = os.path.dirname(full_path)
-    if not os.access(parent, os.R_OK | os.W_OK):
-        raise BadRepoError("Cannot create repository in %s: can't access parent!" % root)
+    config_path = os.path.join(repo_yaml_dir, repo_config_name)
+
+    subdir = _validate_and_normalize_subdir(subdir, root, package_api)
+
+    packages_path = os.path.join(repo_yaml_dir, subdir)
 
     try:
-        config_path = os.path.join(root, repo_config_name)
-        packages_path = os.path.join(root, subdir)
-
         fs.mkdirp(packages_path)
         with open(config_path, "w", encoding="utf-8") as config:
             config.write("repo:\n")
             config.write(f"  namespace: '{namespace}'\n")
             if subdir != packages_dir_name:
                 config.write(f"  subdirectory: '{subdir}'\n")
-            x, y = spack.package_api_version
+            x, y = package_api
             config.write(f"  api: v{x}.{y}\n")
 
     except OSError as e:
@@ -1421,22 +1537,27 @@ def create_repo(root, namespace=None, subdir=packages_dir_name):
 
         raise BadRepoError(
             "Failed to create new repository in %s." % root, "Caused by %s: %s" % (type(e), e)
-        )
+        ) from e
 
-    return full_path, namespace
+    return repo_yaml_dir, namespace
 
 
-def from_path(path: str) -> "Repo":
+def from_path(path: str) -> Repo:
     """Returns a repository from the path passed as input. Injects the global misc cache."""
     return Repo(path, cache=spack.caches.MISC_CACHE)
 
 
-def create_or_construct(path, namespace=None):
+def create_or_construct(
+    root: str,
+    namespace: Optional[str] = None,
+    package_api: Tuple[int, int] = spack.package_api_version,
+) -> Repo:
     """Create a repository, or just return a Repo if it already exists."""
-    if not os.path.exists(path):
-        fs.mkdirp(path)
-        create_repo(path, namespace)
-    return from_path(path)
+    repo_yaml_dir, _ = get_repo_yaml_dir(root, namespace, package_api)
+    if not os.path.exists(repo_yaml_dir):
+        fs.mkdirp(root)
+        create_repo(root, namespace=namespace, package_api=package_api)
+    return from_path(repo_yaml_dir)
 
 
 def _path(configuration=None):
@@ -1514,8 +1635,10 @@ class MockRepositoryBuilder:
     """Build a mock repository in a directory"""
 
     def __init__(self, root_directory, namespace=None):
-        namespace = namespace or "".join(random.choice(string.ascii_uppercase) for _ in range(10))
-        self.root, self.namespace = create_repo(str(root_directory), namespace)
+        namespace = namespace or "".join(random.choice(string.ascii_lowercase) for _ in range(10))
+        repo_root = os.path.join(root_directory, namespace)
+        os.mkdir(repo_root)
+        self.root, self.namespace = create_repo(repo_root, namespace)
 
     def add_package(self, name, dependencies=None):
         """Create a mock package in the repository, using a Jinja2 template.
@@ -1527,7 +1650,7 @@ def add_package(self, name, dependencies=None):
                 ``spack.dependency.default_deptype`` and ``spack.spec.Spec()`` are used.
         """
         dependencies = dependencies or []
-        context = {"cls_name": nm.mod_to_class(name), "dependencies": dependencies}
+        context = {"cls_name": nm.pkg_name_to_class_name(name), "dependencies": dependencies}
         template = spack.tengine.make_environment().get_template("mock-repository/package.pyt")
         text = template.render(context)
         package_py = self.recipe_filename(name)
@@ -1539,8 +1662,10 @@ def remove(self, name):
         package_py = self.recipe_filename(name)
         shutil.rmtree(os.path.dirname(package_py))
 
-    def recipe_filename(self, name):
-        return os.path.join(self.root, "packages", name, "package.py")
+    def recipe_filename(self, name: str):
+        return os.path.join(
+            self.root, "packages", nm.pkg_name_to_pkg_dir(name, package_api=(2, 0)), "package.py"
+        )
 
 
 class RepoError(spack.error.SpackError):
@@ -1590,7 +1715,10 @@ def __init__(self, name, repo=None):
 
                 # 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())
+                try:
+                    similar = difflib.get_close_matches(pkg_name, repo.all_package_names())
+                except Exception:
+                    similar = []
 
                 if 1 <= len(similar) <= 5:
                     long_msg += "\n\nDid you mean one of the following packages?\n  "

lib/spack/spack/schema/config.py

@@ -104,6 +104,7 @@
             "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"}}},
+            "pager": {"type": "array", "items": {"type": "string"}},
         },
         "deprecatedProperties": [
             {

lib/spack/spack/solver/asp.py

@@ -2492,7 +2492,7 @@ def _spec_clauses(
             # TODO: variant="*" means 'variant is defined to something', which used to
             # be meaningless in concretization, as all variants had to be defined. But
             # now that variants can be conditional, it should force a variant to exist.
-            if variant.value == ("*",):
+            if not variant.values:
                 continue
 
             for value in variant.values:

lib/spack/spack/spec.py

@@ -837,7 +837,7 @@ def _shared_subset_pair_iterate(container1, container2):
                 b_idx += 1
 
 
-class FlagMap(lang.HashableMap):
+class FlagMap(lang.HashableMap[str, List[CompilerFlag]]):
     __slots__ = ("spec",)
 
     def __init__(self, spec):
@@ -1861,9 +1861,7 @@ def add_dependency_edge(
     @property
     def fullname(self):
         return (
-            ("%s.%s" % (self.namespace, self.name))
-            if self.namespace
-            else (self.name if self.name else "")
+            f"{self.namespace}.{self.name}" if self.namespace else (self.name if self.name else "")
         )
 
     @property
@@ -4490,7 +4488,7 @@ def has_virtual_dependency(self, virtual: str) -> bool:
         return bool(self.dependencies(virtuals=(virtual,)))
 
 
-class VariantMap(lang.HashableMap):
+class VariantMap(lang.HashableMap[str, vt.VariantValue]):
     """Map containing variant instances. New values can be added only
     if the key is not already present."""
 

lib/spack/spack/test/audit.py

@@ -93,6 +93,7 @@ def test_package_audits(packages, expected_errors, mock_packages):
 ]
 
 
+# TODO/RepoSplit: Should this not rely on mock packages post split?
 @pytest.mark.parametrize(
     "config_section,data,failing_check",
     [
@@ -113,7 +114,7 @@ def test_package_audits(packages, expected_errors, mock_packages):
         ),
     ],
 )
-def test_config_audits(config_section, data, failing_check):
+def test_config_audits(config_section, data, failing_check, mock_packages):
     with spack.config.override(config_section, data):
         reports = spack.audit.run_group("configs")
         assert any((check == failing_check) and errors for check, errors in reports)

lib/spack/spack/test/builder.py

@@ -15,7 +15,7 @@
 
 @pytest.fixture()
 def builder_test_repository(config):
-    builder_test_path = os.path.join(spack.paths.repos_path, "builder.test")
+    builder_test_path = os.path.join(spack.paths.test_repos_path, "builder.test")
     with spack.repo.use_repositories(builder_test_path) as mock_repo:
         yield mock_repo
 

lib/spack/spack/test/cmd/ci.py

@@ -2032,7 +2032,7 @@ def test_ci_verify_versions_valid(
     repo, _, commits = mock_git_package_changes
     spack.repo.PATH.put_first(repo)
 
-    monkeypatch.setattr(spack.repo, "packages_path", mock_packages_path(repo.packages_path))
+    monkeypatch.setattr(spack.repo, "builtin_repo", lambda: repo)
 
     out = ci_cmd("verify-versions", commits[-1], commits[-3])
     assert "Validated diff-test@2.1.5" in out
@@ -2049,7 +2049,7 @@ def test_ci_verify_versions_standard_invalid(
     repo, _, commits = mock_git_package_changes
     spack.repo.PATH.put_first(repo)
 
-    monkeypatch.setattr(spack.repo, "packages_path", mock_packages_path(repo.packages_path))
+    monkeypatch.setattr(spack.repo, "builtin_repo", lambda: repo)
 
     out = ci_cmd("verify-versions", commits[-1], commits[-3], fail_on_error=False)
     assert "Invalid checksum found diff-test@2.1.5" in out
@@ -2060,7 +2060,7 @@ def test_ci_verify_versions_manual_package(monkeypatch, mock_packages, mock_git_
     repo, _, commits = mock_git_package_changes
     spack.repo.PATH.put_first(repo)
 
-    monkeypatch.setattr(spack.repo, "packages_path", mock_packages_path(repo.packages_path))
+    monkeypatch.setattr(spack.repo, "builtin_repo", lambda: repo)
 
     pkg_class = spack.spec.Spec("diff-test").package_class
     monkeypatch.setattr(pkg_class, "manual_download", True)

lib/spack/spack/test/cmd/config.py

@@ -20,6 +20,8 @@
 config = spack.main.SpackCommand("config")
 env = spack.main.SpackCommand("env")
 
+pytestmark = pytest.mark.usefixtures("mock_packages")
+
 
 def _create_config(scope=None, data={}, section="packages"):
     scope = scope or spack.config.default_modify_scope()

lib/spack/spack/test/cmd/env.py

@@ -1829,7 +1829,7 @@ def test_indirect_build_dep(tmp_path):
     build-only dep. Make sure this concrete DAG is preserved when writing the
     environment out and reading it back.
     """
-    builder = spack.repo.MockRepositoryBuilder(tmp_path / "repo")
+    builder = spack.repo.MockRepositoryBuilder(tmp_path)
     builder.add_package("z")
     builder.add_package("y", dependencies=[("z", "build", None)])
     builder.add_package("x", dependencies=[("y", None, None)])
@@ -1862,7 +1862,7 @@ def test_store_different_build_deps(tmp_path):
               z1
 
     """
-    builder = spack.repo.MockRepositoryBuilder(tmp_path / "mirror")
+    builder = spack.repo.MockRepositoryBuilder(tmp_path)
     builder.add_package("z")
     builder.add_package("y", dependencies=[("z", "build", None)])
     builder.add_package("x", dependencies=[("y", None, None), ("z", "build", None)])

lib/spack/spack/test/cmd/info.py

@@ -9,6 +9,8 @@
 import spack.cmd.info
 from spack.main import SpackCommand
 
+pytestmark = [pytest.mark.usefixtures("mock_packages")]
+
 info = SpackCommand("info")
 
 
@@ -31,15 +33,12 @@ def _print(*args, **kwargs):
     return buffer
 
 
-@pytest.mark.parametrize(
-    "pkg", ["openmpi", "trilinos", "boost", "python", "dealii", "xsdk", "gasnet", "warpx"]
-)
 @pytest.mark.parametrize("extra_args", [[], ["--variants-by-name"]])
-def test_it_just_runs(pkg, extra_args):
-    info(pkg, *extra_args)
+def test_it_just_runs(extra_args):
+    info("vtk-m", *extra_args)
 
 
-def test_info_noversion(mock_packages, print_buffer):
+def test_info_noversion(print_buffer):
     """Check that a mock package with no versions outputs None."""
     info("noversion")
 
@@ -58,7 +57,7 @@ def test_info_noversion(mock_packages, print_buffer):
 @pytest.mark.parametrize(
     "pkg_query,expected", [("zlib", "False"), ("find-externals1", "True (version)")]
 )
-def test_is_externally_detectable(mock_packages, pkg_query, expected, parser, print_buffer):
+def test_is_externally_detectable(pkg_query, expected, parser, print_buffer):
     args = parser.parse_args(["--detectable", pkg_query])
     spack.cmd.info.info(parser, args)
 
@@ -70,13 +69,7 @@ def test_is_externally_detectable(mock_packages, pkg_query, expected, parser, pr
 
 
 @pytest.mark.parametrize(
-    "pkg_query",
-    [
-        "hdf5",
-        "cloverleaf3d",
-        "trilinos",
-        "gcc",  # This should ensure --test's c_names processing loop covered
-    ],
+    "pkg_query", ["vtk-m", "gcc"]  # This should ensure --test's c_names processing loop covered
 )
 @pytest.mark.parametrize("extra_args", [[], ["--variants-by-name"]])
 def test_info_fields(pkg_query, extra_args, parser, print_buffer):

lib/spack/spack/test/cmd/list.py

@@ -6,16 +6,20 @@
 import sys
 from textwrap import dedent
 
+import pytest
+
 import spack.paths
 import spack.repo
 from spack.main import SpackCommand
 
+pytestmark = [pytest.mark.usefixtures("mock_packages")]
+
 list = SpackCommand("list")
 
 
 def test_list():
     output = list()
-    assert "cloverleaf3d" in output
+    assert "bzip2" in output
     assert "hdf5" in output
 
 
@@ -41,7 +45,7 @@ def test_list_cli_output_format(mock_tty_stdout):
     assert out == out_str
 
 
-def test_list_filter(mock_packages):
+def test_list_filter():
     output = list("py-*")
     assert "py-extension1" in output
     assert "py-extension2" in output
@@ -57,18 +61,18 @@ def test_list_filter(mock_packages):
     assert "mpich" not in output
 
 
-def test_list_search_description(mock_packages):
+def test_list_search_description():
     output = list("--search-description", "one build dependency")
     assert "depb" in output
 
 
-def test_list_format_name_only(mock_packages):
+def test_list_format_name_only():
     output = list("--format", "name_only")
     assert "zmpi" in output
     assert "hdf5" in output
 
 
-def test_list_format_version_json(mock_packages):
+def test_list_format_version_json():
     output = list("--format", "version_json")
     assert '{"name": "zmpi",' in output
     assert '{"name": "dyninst",' in output
@@ -77,7 +81,7 @@ def test_list_format_version_json(mock_packages):
     json.loads(output)
 
 
-def test_list_format_html(mock_packages):
+def test_list_format_html():
     output = list("--format", "html")
     assert '<div class="section" id="zmpi">' in output
     assert "<h1>zmpi" in output
@@ -86,7 +90,7 @@ def test_list_format_html(mock_packages):
     assert "<h1>hdf5" in output
 
 
-def test_list_update(tmpdir, mock_packages):
+def test_list_update(tmpdir):
     update_file = tmpdir.join("output")
 
     # not yet created when list is run
@@ -113,7 +117,7 @@ def test_list_update(tmpdir, mock_packages):
         assert f.read() == "empty\n"
 
 
-def test_list_tags(mock_packages):
+def test_list_tags():
     output = list("--tag", "tag1")
     assert "mpich" in output
     assert "mpich2" in output
@@ -127,7 +131,7 @@ def test_list_tags(mock_packages):
     assert "mpich2" in output
 
 
-def test_list_count(mock_packages):
+def test_list_count():
     output = list("--count")
     assert int(output.strip()) == len(spack.repo.all_package_names())
 
@@ -137,11 +141,10 @@ def test_list_count(mock_packages):
     )
 
 
-# def test_list_repos(mock_packages, builder_test_repository):
 def test_list_repos():
     with spack.repo.use_repositories(
-        os.path.join(spack.paths.repos_path, "builtin.mock"),
-        os.path.join(spack.paths.repos_path, "builder.test"),
+        os.path.join(spack.paths.test_repos_path, "builtin.mock"),
+        os.path.join(spack.paths.test_repos_path, "builder.test"),
     ):
         total_pkgs = len(list().strip().split())
         mock_pkgs = len(list("-r", "builtin.mock").strip().split())

lib/spack/spack/test/cmd/pkg.py

@@ -111,12 +111,12 @@ def split(output):
 pkg = spack.main.SpackCommand("pkg")
 
 
-def test_packages_path():
-    assert spack.repo.packages_path() == spack.repo.PATH.get_repo("builtin").packages_path
+def test_builtin_repo():
+    assert spack.repo.builtin_repo() is spack.repo.PATH.get_repo("builtin")
 
 
-def test_mock_packages_path(mock_packages):
-    assert spack.repo.packages_path() == spack.repo.PATH.get_repo("builtin.mock").packages_path
+def test_mock_builtin_repo(mock_packages):
+    assert spack.repo.builtin_repo() is spack.repo.PATH.get_repo("builtin.mock")
 
 
 def test_pkg_add(git, mock_pkg_git_repo):

lib/spack/spack/test/cmd/repo.py

@@ -2,6 +2,7 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import os
+import pathlib
 
 import pytest
 
@@ -22,19 +23,19 @@ def test_help_option():
     assert repo.returncode in (None, 0)
 
 
-def test_create_add_list_remove(mutable_config, tmpdir):
+def test_create_add_list_remove(mutable_config, tmp_path: pathlib.Path):
     # Create a new repository and check that the expected
     # files are there
-    repo("create", str(tmpdir), "mockrepo")
-    assert os.path.exists(os.path.join(str(tmpdir), "repo.yaml"))
+    repo("create", str(tmp_path), "mockrepo")
+    assert (tmp_path / "spack_repo" / "mockrepo" / "repo.yaml").exists()
 
     # Add the new repository and check it appears in the list output
-    repo("add", "--scope=site", str(tmpdir))
+    repo("add", "--scope=site", str(tmp_path / "spack_repo" / "mockrepo"))
     output = repo("list", "--scope=site", output=str)
     assert "mockrepo" in output
 
     # Then remove it and check it's not there
-    repo("remove", "--scope=site", str(tmpdir))
+    repo("remove", "--scope=site", str(tmp_path / "spack_repo" / "mockrepo"))
     output = repo("list", "--scope=site", output=str)
     assert "mockrepo" not in output
 

lib/spack/spack/test/cmd/style.py

@@ -116,7 +116,7 @@ def test_changed_no_base(git, tmpdir, capfd):
         assert "This repository does not have a 'foobar'" in err
 
 
-def test_changed_files_all_files():
+def test_changed_files_all_files(mock_packages):
     # it's hard to guarantee "all files", so do some sanity checks.
     files = set(
         [
@@ -159,8 +159,12 @@ def test_bad_root(tmpdir):
 
 def test_style_is_package(tmpdir):
     """Ensure the is_package() function works."""
-    assert spack.cmd.style.is_package("var/spack/repos/builtin/packages/hdf5/package.py")
-    assert spack.cmd.style.is_package("var/spack/repos/builtin/packages/zlib/package.py")
+    assert spack.cmd.style.is_package(
+        "var/spack/repos/spack_repo/builtin/packages/hdf5/package.py"
+    )
+    assert spack.cmd.style.is_package(
+        "var/spack/repos/spack_repo/builtin/packages/zlib/package.py"
+    )
     assert not spack.cmd.style.is_package("lib/spack/spack/spec.py")
     assert not spack.cmd.style.is_package("lib/spack/external/pytest.py")
 

lib/spack/spack/test/cmd/versions.py

@@ -10,6 +10,9 @@
 versions = SpackCommand("versions")
 
 
+pytestmark = [pytest.mark.usefixtures("mock_packages")]
+
+
 def test_safe_versions():
     """Only test the safe versions of a package."""
 
@@ -70,11 +73,11 @@ def test_no_unchecksummed_versions():
 def test_versions_no_url():
     """Test a package with versions but without a ``url`` attribute."""
 
-    versions("graphviz")
+    versions("attributes-foo-app")
 
 
 @pytest.mark.maybeslow
 def test_no_versions_no_url():
     """Test a package without versions or a ``url`` attribute."""
 
-    versions("opengl")
+    versions("no-url-or-version")

lib/spack/spack/test/concretization/compiler_runtimes.py

@@ -29,7 +29,7 @@ def _concretize_with_reuse(*, root_str, reused_str):
 
 @pytest.fixture
 def runtime_repo(mutable_config):
-    repo = os.path.join(spack.paths.repos_path, "compiler_runtime.test")
+    repo = os.path.join(spack.paths.test_repos_path, "compiler_runtime.test")
     with spack.repo.use_repositories(repo) as mock_repo:
         yield mock_repo
 

lib/spack/spack/test/concretization/core.py

@@ -1719,7 +1719,7 @@ def test_reuse_with_unknown_namespace_dont_raise(
 
     @pytest.mark.regression("45538")
     def test_reuse_from_other_namespace_no_raise(self, tmpdir, temporary_store, monkeypatch):
-        myrepo = spack.repo.MockRepositoryBuilder(tmpdir.mkdir("mock.repo"), namespace="myrepo")
+        myrepo = spack.repo.MockRepositoryBuilder(tmpdir, namespace="mock_repo")
         myrepo.add_package("zlib")
 
         builtin = spack.concretize.concretize_one("zlib")
@@ -1727,21 +1727,19 @@ def test_reuse_from_other_namespace_no_raise(self, tmpdir, temporary_store, monk
 
         with spack.repo.use_repositories(myrepo.root, override=False):
             with spack.config.override("concretizer:reuse", True):
-                myrepo = spack.concretize.concretize_one("myrepo.zlib")
+                myrepo = spack.concretize.concretize_one("mock_repo.zlib")
 
-        assert myrepo.namespace == "myrepo"
+        assert myrepo.namespace == "mock_repo"
 
     @pytest.mark.regression("28259")
     def test_reuse_with_unknown_package_dont_raise(self, tmpdir, temporary_store, monkeypatch):
-        builder = spack.repo.MockRepositoryBuilder(tmpdir.mkdir("mock.repo"), namespace="myrepo")
+        builder = spack.repo.MockRepositoryBuilder(str(tmpdir), namespace="myrepo")
         builder.add_package("pkg-c")
         with spack.repo.use_repositories(builder.root, override=False):
             s = spack.concretize.concretize_one("pkg-c")
             assert s.namespace == "myrepo"
             PackageInstaller([s.package], fake=True, explicit=True).install()
-
-        del sys.modules["spack.pkg.myrepo.pkg-c"]
-        del sys.modules["spack.pkg.myrepo"]
+        del sys.modules["spack_repo.myrepo.packages.pkg_c"]
         builder.remove("pkg-c")
         with spack.repo.use_repositories(builder.root, override=False) as repos:
             # TODO (INJECT CONFIGURATION): unclear why the cache needs to be invalidated explicitly
@@ -2334,7 +2332,7 @@ def test_select_lower_priority_package_from_repository_stack(
         from cli.
         """
         # 'builtin.mock" and "duplicates.test" share a 'gmake' package
-        additional_repo = os.path.join(spack.paths.repos_path, "duplicates.test")
+        additional_repo = os.path.join(spack.paths.test_repos_path, "duplicates.test")
         with spack.repo.use_repositories(additional_repo, override=False):
             s = spack.concretize.concretize_one(spec_str)
 
@@ -2578,7 +2576,7 @@ def test_correct_external_is_selected_from_packages_yaml(self, mutable_config):
 
 @pytest.fixture()
 def duplicates_test_repository():
-    repository_path = os.path.join(spack.paths.repos_path, "duplicates.test")
+    repository_path = os.path.join(spack.paths.test_repos_path, "duplicates.test")
     with spack.repo.use_repositories(repository_path) as mock_repo:
         yield mock_repo
 
@@ -2813,7 +2811,7 @@ def test_adding_specs(self, input_specs, default_mock_concretization):
 
 @pytest.fixture()
 def edges_test_repository():
-    repository_path = os.path.join(spack.paths.repos_path, "edges.test")
+    repository_path = os.path.join(spack.paths.test_repos_path, "edges.test")
     with spack.repo.use_repositories(repository_path) as mock_repo:
         yield mock_repo
 
@@ -3107,7 +3105,9 @@ def test_spec_unification(unify, mutable_config, mock_packages):
         _ = spack.cmd.parse_specs([a_restricted, b], concretize=True)
 
 
-def test_concretization_cache_roundtrip(use_concretization_cache, monkeypatch, mutable_config):
+def test_concretization_cache_roundtrip(
+    mock_packages, use_concretization_cache, monkeypatch, mutable_config
+):
     """Tests whether we can write the results of a clingo solve to the cache
     and load the same spec request from the cache to produce identical specs"""
     # Force determinism:

lib/spack/spack/test/concretization/flag_mixing.py

@@ -46,7 +46,7 @@
 
 @pytest.fixture
 def test_repo(mutable_config, monkeypatch, mock_stage):
-    repo_dir = pathlib.Path(spack.paths.repos_path) / "flags.test"
+    repo_dir = pathlib.Path(spack.paths.test_repos_path) / "flags.test"
     with spack.repo.use_repositories(str(repo_dir)) as mock_repo_path:
         yield mock_repo_path
 

lib/spack/spack/test/concretization/requirements.py

@@ -28,7 +28,7 @@ def update_packages_config(conf_str):
 
 @pytest.fixture
 def test_repo(mutable_config, monkeypatch, mock_stage):
-    repo_dir = pathlib.Path(spack.paths.repos_path) / "requirements.test"
+    repo_dir = pathlib.Path(spack.paths.test_repos_path) / "requirements.test"
     with spack.repo.use_repositories(str(repo_dir)) as mock_repo_path:
         yield mock_repo_path
 

lib/spack/spack/test/config.py

@@ -914,7 +914,7 @@ def test_single_file_scope(config, env_yaml):
         assert spack.config.get("config:checksum") is True
         assert spack.config.get("config:checksum") is True
         assert spack.config.get("packages:externalmodule:buildable") is False
-        assert spack.config.get("repos") == ["/x/y/z", "$spack/var/spack/repos/builtin"]
+        assert spack.config.get("repos") == ["/x/y/z", "$spack/var/spack/repos/spack_repo/builtin"]
 
 
 def test_single_file_scope_section_override(tmpdir, config):
@@ -950,7 +950,7 @@ def test_single_file_scope_section_override(tmpdir, config):
         # from the lower config scopes
         assert spack.config.get("config:checksum") is True
         assert not spack.config.get("packages:externalmodule")
-        assert spack.config.get("repos") == ["/x/y/z", "$spack/var/spack/repos/builtin"]
+        assert spack.config.get("repos") == ["/x/y/z", "$spack/var/spack/repos/spack_repo/builtin"]
 
 
 def test_write_empty_single_file_scope(tmpdir):

lib/spack/spack/test/conftest.py

@@ -259,9 +259,9 @@ def mock_git_package_changes(git, tmpdir, override_git_repos_cache_path, monkeyp
     Important attributes of the repo for test coverage are: multiple package
     versions are added with some coming from a tarball and some from git refs.
     """
-    filename = "diff-test/package.py"
+    filename = "diff_test/package.py"
 
-    repo_path, _ = spack.repo.create_repo(str(tmpdir.mkdir("myrepo")))
+    repo_path, _ = spack.repo.create_repo(str(tmpdir), namespace="myrepo")
     repo_cache = spack.util.file_cache.FileCache(str(tmpdir.mkdir("cache")))
 
     repo = spack.repo.Repo(repo_path, cache=repo_cache)

lib/spack/spack/test/data/config/repos.yaml

@@ -1,2 +1,2 @@
 repos:
-  - $spack/var/spack/repos/builtin
+  - $spack/var/spack/repos/spack_repo/builtin

lib/spack/spack/test/package_class.py

@@ -246,22 +246,29 @@ class BadDetectablePackage(spack.package.Package):
 
 
 def test_package_url_and_urls():
-    class URLsPackage(spack.package.Package):
-        url = "https://www.example.com/url-package-1.0.tgz"
-        urls = ["https://www.example.com/archive"]
+    UrlsPackage = type(
+        "URLsPackage",
+        (spack.package.Package,),
+        {
+            "__module__": "spack.pkg.builtin.urls_package",
+            "url": "https://www.example.com/url-package-1.0.tgz",
+            "urls": ["https://www.example.com/archive"],
+        },
+    )
 
-    s = spack.spec.Spec("pkg-a")
+    s = spack.spec.Spec("urls-package")
     with pytest.raises(ValueError, match="defines both"):
-        URLsPackage(s)
+        UrlsPackage(s)
 
 
 def test_package_license():
-    class LicensedPackage(spack.package.Package):
-        extendees = None  # currently a required attribute for is_extension()
-        license_files = None
+    LicensedPackage = type(
+        "LicensedPackage",
+        (spack.package.Package,),
+        {"__module__": "spack.pkg.builtin.licensed_package"},
+    )
 
-    s = spack.spec.Spec("pkg-a")
-    pkg = LicensedPackage(s)
+    pkg = LicensedPackage(spack.spec.Spec("licensed-package"))
     assert pkg.global_license_file is None
 
     pkg.license_files = ["license.txt"]

lib/spack/spack/test/packages.py

@@ -15,7 +15,7 @@
 import spack.repo
 from spack.paths import mock_packages_path
 from spack.spec import Spec
-from spack.util.naming import mod_to_class
+from spack.util.naming import pkg_name_to_class_name
 from spack.version import VersionChecksumError
 
 
@@ -47,11 +47,15 @@ def test_nonexisting_package_filename(self):
         )
 
     def test_package_class_names(self):
-        assert "Mpich" == mod_to_class("mpich")
-        assert "PmgrCollective" == mod_to_class("pmgr_collective")
-        assert "PmgrCollective" == mod_to_class("pmgr-collective")
-        assert "Pmgrcollective" == mod_to_class("PmgrCollective")
-        assert "_3db" == mod_to_class("3db")
+        assert "Mpich" == pkg_name_to_class_name("mpich")
+        assert "PmgrCollective" == pkg_name_to_class_name("pmgr_collective")
+        assert "PmgrCollective" == pkg_name_to_class_name("pmgr-collective")
+        assert "Pmgrcollective" == pkg_name_to_class_name("PmgrCollective")
+        assert "_3db" == pkg_name_to_class_name("3db")
+        assert "_True" == pkg_name_to_class_name("true")  # reserved keyword
+        assert "_False" == pkg_name_to_class_name("false")  # reserved keyword
+        assert "_None" == pkg_name_to_class_name("none")  # reserved keyword
+        assert "Finally" == pkg_name_to_class_name("finally")  # `Finally` is not reserved
 
     # Below tests target direct imports of spack packages from the
     # spack.pkg namespace
@@ -333,3 +337,16 @@ def test_package_can_have_sparse_checkout_properties(mock_packages, mock_fetch,
     assert isinstance(fetcher, spack.fetch_strategy.GitFetchStrategy)
     assert hasattr(fetcher, "git_sparse_paths")
     assert fetcher.git_sparse_paths == pkg_cls.git_sparse_paths
+
+
+def test_pkg_name_can_only_be_derived_when_package_module():
+    """When the module prefix is not spack_repo (or legacy spack.pkg) we cannot derive
+    a package name."""
+    ExamplePackage = type(
+        "ExamplePackage",
+        (spack.package_base.PackageBase,),
+        {"__module__": "not.a.spack.repo.packages.example_package.package"},
+    )
+
+    with pytest.raises(ValueError, match="Package ExamplePackage is not a known Spack package"):
+        ExamplePackage.name

lib/spack/spack/test/repo.py

@@ -6,11 +6,14 @@
 
 import pytest
 
+import spack
 import spack.package_base
 import spack.paths
 import spack.repo
 import spack.spec
 import spack.util.file_cache
+import spack.util.naming
+from spack.util.naming import valid_module_name
 
 
 @pytest.fixture(params=["packages", "", "foo"])
@@ -184,12 +187,12 @@ def _repo_paths(repos):
                 repo_paths.append(spack.paths.mock_packages_path)
                 namespaces.append("builtin.mock")
             if entry == "extra":
-                name = "extra.mock"
+                name = "extra_mock"
                 repo_dir = tmp_path / name
                 repo_dir.mkdir()
-                _ = spack.repo.MockRepositoryBuilder(repo_dir, name)
-                repo_paths.append(str(repo_dir))
-                namespaces.append(name)
+                repo = spack.repo.MockRepositoryBuilder(repo_dir, name)
+                repo_paths.append(repo.root)
+                namespaces.append(repo.namespace)
         return repo_paths, namespaces
 
     repo_paths, namespaces = _repo_paths(repos)
@@ -216,7 +219,7 @@ def test_use_repositories_and_import():
     """Tests that use_repositories changes the import search too"""
     import spack.paths
 
-    repo_dir = pathlib.Path(spack.paths.repos_path)
+    repo_dir = pathlib.Path(spack.paths.test_repos_path)
     with spack.repo.use_repositories(str(repo_dir / "compiler_runtime.test")):
         import spack.pkg.compiler_runtime.test.gcc_runtime
 
@@ -310,7 +313,7 @@ def test_creation_from_string(self, mock_test_cache):
         repo = spack.repo.RepoPath(spack.paths.mock_packages_path, cache=mock_test_cache)
         assert len(repo.repos) == 1
         assert repo.repos[0]._finder is repo
-        assert repo.by_namespace["spack.pkg.builtin.mock"] is repo.repos[0]
+        assert repo.by_namespace["builtin.mock"] is repo.repos[0]
 
     def test_get_repo(self, mock_test_cache):
         repo = spack.repo.RepoPath(spack.paths.mock_packages_path, cache=mock_test_cache)
@@ -364,3 +367,160 @@ def test_repo_package_api_version(tmp_path: pathlib.Path):
     )
     cache = spack.util.file_cache.FileCache(tmp_path / "cache")
     assert spack.repo.Repo(str(tmp_path / "example"), cache=cache).package_api == (1, 0)
+
+
+def test_mod_to_pkg_name_and_reverse():
+    # In repo v1 the dirname/module name is the package name
+    assert spack.util.naming.pkg_dir_to_pkg_name("zlib_ng", package_api=(1, 0)) == "zlib_ng"
+    assert (
+        spack.util.naming.pkg_dir_to_pkg_name("_3example_4", package_api=(1, 0)) == "_3example_4"
+    )
+    assert spack.util.naming.pkg_name_to_pkg_dir("zlib_ng", package_api=(1, 0)) == "zlib_ng"
+    assert (
+        spack.util.naming.pkg_name_to_pkg_dir("_3example_4", package_api=(1, 0)) == "_3example_4"
+    )
+
+    # In repo v2 there is a 1-1 mapping between module and package names
+    assert spack.util.naming.pkg_dir_to_pkg_name("_3example_4", package_api=(2, 0)) == "3example-4"
+    assert spack.util.naming.pkg_dir_to_pkg_name("zlib_ng", package_api=(2, 0)) == "zlib-ng"
+    assert spack.util.naming.pkg_name_to_pkg_dir("zlib-ng", package_api=(2, 0)) == "zlib_ng"
+    assert spack.util.naming.pkg_name_to_pkg_dir("3example-4", package_api=(2, 0)) == "_3example_4"
+
+    # reserved names need an underscore
+    assert spack.util.naming.pkg_dir_to_pkg_name("_finally", package_api=(2, 0)) == "finally"
+    assert spack.util.naming.pkg_dir_to_pkg_name("_assert", package_api=(2, 0)) == "assert"
+    assert spack.util.naming.pkg_name_to_pkg_dir("finally", package_api=(2, 0)) == "_finally"
+    assert spack.util.naming.pkg_name_to_pkg_dir("assert", package_api=(2, 0)) == "_assert"
+
+    # reserved names are case sensitive, so true/false/none are ok
+    assert spack.util.naming.pkg_dir_to_pkg_name("true", package_api=(2, 0)) == "true"
+    assert spack.util.naming.pkg_dir_to_pkg_name("none", package_api=(2, 0)) == "none"
+    assert spack.util.naming.pkg_name_to_pkg_dir("true", package_api=(2, 0)) == "true"
+    assert spack.util.naming.pkg_name_to_pkg_dir("none", package_api=(2, 0)) == "none"
+
+
+def test_repo_v2_invalid_module_name(tmp_path: pathlib.Path, capsys):
+    # Create a repo with a v2 structure
+    root, _ = spack.repo.create_repo(str(tmp_path), namespace="repo_1", package_api=(2, 0))
+    repo_dir = pathlib.Path(root)
+
+    # Create two invalid module names
+    (repo_dir / "packages" / "zlib-ng").mkdir()
+    (repo_dir / "packages" / "zlib-ng" / "package.py").write_text(
+        """
+from spack.package import Package
+
+class ZlibNg(Package):
+    pass
+"""
+    )
+    (repo_dir / "packages" / "UPPERCASE").mkdir()
+    (repo_dir / "packages" / "UPPERCASE" / "package.py").write_text(
+        """
+from spack.package import Package
+
+class Uppercase(Package):
+    pass
+"""
+    )
+
+    with spack.repo.use_repositories(str(repo_dir)) as repo:
+        assert len(repo.all_package_names()) == 0
+
+    stderr = capsys.readouterr().err
+    assert "cannot be used because `zlib-ng` is not a valid Spack package module name" in stderr
+    assert "cannot be used because `UPPERCASE` is not a valid Spack package module name" in stderr
+
+
+def test_repo_v2_module_and_class_to_package_name(tmp_path: pathlib.Path, capsys):
+    # Create a repo with a v2 structure
+    root, _ = spack.repo.create_repo(str(tmp_path), namespace="repo_2", package_api=(2, 0))
+    repo_dir = pathlib.Path(root)
+
+    # Create an invalid module name
+    (repo_dir / "packages" / "_1example_2_test").mkdir()
+    (repo_dir / "packages" / "_1example_2_test" / "package.py").write_text(
+        """
+from spack.package import Package
+
+class _1example2Test(Package):
+    pass
+"""
+    )
+
+    with spack.repo.use_repositories(str(repo_dir)) as repo:
+        assert repo.exists("1example-2-test")
+        pkg_cls = repo.get_pkg_class("1example-2-test")
+        assert pkg_cls.name == "1example-2-test"
+        assert pkg_cls.module.__name__ == "spack_repo.repo_2.packages._1example_2_test.package"
+
+
+def test_valid_module_name_v2():
+    api = (2, 0)
+
+    # no hyphens
+    assert not valid_module_name("zlib-ng", api)
+
+    # cannot start with a number
+    assert not valid_module_name("7zip", api)
+
+    # no consecutive underscores
+    assert not valid_module_name("zlib__ng", api)
+
+    # reserved names
+    assert not valid_module_name("finally", api)
+    assert not valid_module_name("assert", api)
+
+    # cannot contain uppercase
+    assert not valid_module_name("False", api)
+    assert not valid_module_name("zlib_NG", api)
+
+    # reserved names are allowed when preceded by underscore
+    assert valid_module_name("_finally", api)
+    assert valid_module_name("_assert", api)
+
+    # digits are allowed when preceded by underscore
+    assert valid_module_name("_1example_2_test", api)
+
+    # underscore is not allowed unless followed by reserved name or digit
+    assert not valid_module_name("_zlib", api)
+    assert not valid_module_name("_false", api)
+
+
+def test_namespace_is_optional_in_v2(tmp_path: pathlib.Path):
+    """Test that a repo without a namespace is valid in v2."""
+    repo_yaml_dir = tmp_path / "spack_repo" / "foo" / "bar" / "baz"
+    (repo_yaml_dir / "packages").mkdir(parents=True)
+    (repo_yaml_dir / "repo.yaml").write_text(
+        """\
+repo:
+  api: v2.0
+"""
+    )
+
+    cache = spack.util.file_cache.FileCache(tmp_path / "cache")
+    repo = spack.repo.Repo(str(repo_yaml_dir), cache=cache)
+
+    assert repo.namespace == "foo.bar.baz"
+    assert repo.full_namespace == "spack_repo.foo.bar.baz.packages"
+    assert repo.root == str(repo_yaml_dir)
+    assert repo.packages_path == str(repo_yaml_dir / "packages")
+    assert repo.python_path == str(tmp_path)
+    assert repo.package_api == (2, 0)
+
+
+def test_subdir_in_v2():
+    """subdir cannot be . or empty in v2, because otherwise we cannot statically distinguish
+    between namespace and subdir."""
+    with pytest.raises(spack.repo.BadRepoError, match="Use a symlink packages -> . instead"):
+        spack.repo._validate_and_normalize_subdir(subdir="", root="root", package_api=(2, 0))
+
+    with pytest.raises(spack.repo.BadRepoError, match="Use a symlink packages -> . instead"):
+        spack.repo._validate_and_normalize_subdir(subdir=".", root="root", package_api=(2, 0))
+
+    with pytest.raises(spack.repo.BadRepoError, match="Expected a directory name, not a path"):
+        subdir = os.path.join("a", "b")
+        spack.repo._validate_and_normalize_subdir(subdir=subdir, root="root", package_api=(2, 0))
+
+    with pytest.raises(spack.repo.BadRepoError, match="Must be a valid Python module name"):
+        spack.repo._validate_and_normalize_subdir(subdir="123", root="root", package_api=(2, 0))

lib/spack/spack/util/naming.py

@@ -6,72 +6,107 @@
 import itertools
 import re
 import string
-
-import spack.error
+from typing import List, Tuple
 
 __all__ = [
-    "mod_to_class",
-    "spack_module_to_python_module",
+    "pkg_name_to_class_name",
     "valid_module_name",
-    "valid_fully_qualified_module_name",
-    "validate_fully_qualified_module_name",
-    "validate_module_name",
     "possible_spack_module_names",
     "simplify_name",
     "NamespaceTrie",
 ]
 
-# Valid module names can contain '-' but can't start with it.
-_valid_module_re = r"^\w[\w-]*$"
+#: see keyword.kwlist: https://github.com/python/cpython/blob/main/Lib/keyword.py
+RESERVED_NAMES_ONLY_LOWERCASE = frozenset(
+    (
+        "and",
+        "as",
+        "assert",
+        "async",
+        "await",
+        "break",
+        "class",
+        "continue",
+        "def",
+        "del",
+        "elif",
+        "else",
+        "except",
+        "finally",
+        "for",
+        "from",
+        "global",
+        "if",
+        "import",
+        "in",
+        "is",
+        "lambda",
+        "nonlocal",
+        "not",
+        "or",
+        "pass",
+        "raise",
+        "return",
+        "try",
+        "while",
+        "with",
+        "yield",
+    )
+)
+
+RESERVED_NAMES_LIST_MIXED_CASE = ("False", "None", "True")
 
 # Valid module names can contain '-' but can't start with it.
-_valid_fully_qualified_module_re = r"^(\w[\w-]*)(\.\w[\w-]*)*$"
+_VALID_MODULE_RE_V1 = re.compile(r"^\w[\w-]*$")
+
+_VALID_MODULE_RE_V2 = re.compile(r"^[a-z_][a-z0-9_]*$")
 
 
-def mod_to_class(mod_name):
-    """Convert a name from module style to class name style.  Spack mostly
-    follows `PEP-8 <http://legacy.python.org/dev/peps/pep-0008/>`_:
+def pkg_name_to_class_name(pkg_name: str):
+    """Convert a Spack package name to a class name, based on
+    `PEP-8 <http://legacy.python.org/dev/peps/pep-0008/>`_:
 
        * Module and package names use lowercase_with_underscores.
        * Class names use the CapWords convention.
 
-    Regular source code follows these convetions.  Spack is a bit
-    more liberal with its Package names and Compiler names:
+    Not all package names are valid Python identifiers:
 
-       * They can contain '-' as well as '_', but cannot start with '-'.
+       * They can contain '-', but cannot start with '-'.
        * They can start with numbers, e.g. "3proxy".
 
-    This function converts from the module convention to the class
-    convention by removing _ and - and converting surrounding
-    lowercase text to CapWords.  If mod_name starts with a number,
-    the class name returned will be prepended with '_' to make a
-    valid Python identifier.
+    This function converts from the package name to the class convention by removing _ and - and
+    converting surrounding lowercase text to CapWords.  If package name starts with a number, the
+    class name returned will be prepended with '_' to make a valid Python identifier.
     """
-    validate_module_name(mod_name)
-
-    class_name = re.sub(r"[-_]+", "-", mod_name)
+    class_name = re.sub(r"[-_]+", "-", pkg_name)
     class_name = string.capwords(class_name, "-")
     class_name = class_name.replace("-", "")
 
-    # If a class starts with a number, prefix it with Number_ to make it
-    # a valid Python class name.
-    if re.match(r"^[0-9]", class_name):
-        class_name = "_%s" % class_name
+    # Ensure that the class name is a valid Python identifier
+    if re.match(r"^[0-9]", class_name) or class_name in RESERVED_NAMES_LIST_MIXED_CASE:
+        class_name = f"_{class_name}"
 
     return class_name
 
 
-def spack_module_to_python_module(mod_name):
-    """Given a Spack module name, returns the name by which it can be
-    imported in Python.
-    """
-    if re.match(r"[0-9]", mod_name):
-        mod_name = "num" + mod_name
-
-    return mod_name.replace("-", "_")
+def pkg_dir_to_pkg_name(dirname: str, package_api: Tuple[int, int]) -> str:
+    """Translate a package dir (pkg_dir/package.py) to its corresponding package name"""
+    if package_api < (2, 0):
+        return dirname
+    return dirname.lstrip("_").replace("_", "-")
 
 
-def possible_spack_module_names(python_mod_name):
+def pkg_name_to_pkg_dir(name: str, package_api: Tuple[int, int]) -> str:
+    """Translate a package name to its corresponding package dir (pkg_dir/package.py)"""
+    if package_api < (2, 0):
+        return name
+    name = name.replace("-", "_")
+    if re.match(r"^[0-9]", name) or name in RESERVED_NAMES_ONLY_LOWERCASE:
+        name = f"_{name}"
+    return name
+
+
+def possible_spack_module_names(python_mod_name: str) -> List[str]:
     """Given a Python module name, return a list of all possible spack module
     names that could correspond to it."""
     mod_name = re.sub(r"^num(\d)", r"\1", python_mod_name)
@@ -79,7 +114,7 @@ def possible_spack_module_names(python_mod_name):
     parts = re.split(r"(_)", mod_name)
     options = [["_", "-"]] * mod_name.count("_")
 
-    results = []
+    results: List[str] = []
     for subs in itertools.product(*options):
         s = list(parts)
         s[1::2] = subs
@@ -88,7 +123,7 @@ def possible_spack_module_names(python_mod_name):
     return results
 
 
-def simplify_name(name):
+def simplify_name(name: str) -> str:
     """Simplify package name to only lowercase, digits, and dashes.
 
     Simplifies a name which may include uppercase letters, periods,
@@ -136,42 +171,17 @@ def simplify_name(name):
     return name
 
 
-def valid_module_name(mod_name):
+def valid_module_name(mod_name: str, package_api: Tuple[int, int]) -> bool:
     """Return whether mod_name is valid for use in Spack."""
-    return bool(re.match(_valid_module_re, mod_name))
-
-
-def valid_fully_qualified_module_name(mod_name):
-    """Return whether mod_name is a valid namespaced module name."""
-    return bool(re.match(_valid_fully_qualified_module_re, mod_name))
-
-
-def validate_module_name(mod_name):
-    """Raise an exception if mod_name is not valid."""
-    if not valid_module_name(mod_name):
-        raise InvalidModuleNameError(mod_name)
-
-
-def validate_fully_qualified_module_name(mod_name):
-    """Raise an exception if mod_name is not a valid namespaced module name."""
-    if not valid_fully_qualified_module_name(mod_name):
-        raise InvalidFullyQualifiedModuleNameError(mod_name)
-
-
-class InvalidModuleNameError(spack.error.SpackError):
-    """Raised when we encounter a bad module name."""
-
-    def __init__(self, name):
-        super().__init__("Invalid module name: " + name)
-        self.name = name
-
-
-class InvalidFullyQualifiedModuleNameError(spack.error.SpackError):
-    """Raised when we encounter a bad full package name."""
-
-    def __init__(self, name):
-        super().__init__("Invalid fully qualified package name: " + name)
-        self.name = name
+    if package_api < (2, 0):
+        return bool(_VALID_MODULE_RE_V1.match(mod_name))
+    elif not _VALID_MODULE_RE_V2.match(mod_name) or "__" in mod_name:
+        return False
+    elif mod_name.startswith("_"):
+        # it can only start with an underscore if followed by digit or reserved name
+        return mod_name[1:] in RESERVED_NAMES_ONLY_LOWERCASE or mod_name[1].isdigit()
+    else:
+        return mod_name not in RESERVED_NAMES_ONLY_LOWERCASE
 
 
 class NamespaceTrie:

pyproject.toml

@@ -99,12 +99,12 @@ archspec = ["archspec"]
 llnl = ["llnl"]
 
 [tool.ruff.lint.per-file-ignores]
-"var/spack/repos/*/package.py" = ["F403", "F405", "F811", "F821"]
+"var/spack/*/package.py" = ["F403", "F405", "F811", "F821"]
 "*-ci-package.py" = ["F403", "F405", "F821"]
 
 [tool.black]
 line-length = 99
-include = '(lib/spack|var/spack/repos)/.*\.pyi?$|bin/spack$'
+include = '(lib/spack|var/spack/repos|var/spack/test_repos)/.*\.pyi?$|bin/spack$'
 extend-exclude = 'lib/spack/external'
 skip_magic_trailing_comma = true
 
@@ -126,8 +126,16 @@ src_paths = "lib"
 honor_noqa = true
 
 [tool.mypy]
-files = ['lib/spack/llnl/**/*.py', 'lib/spack/spack/**/*.py', './var/spack/repos/builtin/packages/*/package.py']
-mypy_path = ['bin', 'lib/spack', 'lib/spack/external', 'var/spack/repos/builtin']
+files = [
+  "lib/spack/llnl/**/*.py",
+  "lib/spack/spack/**/*.py",
+  "var/spack/repos/spack_repo/builtin/packages/*/package.py"
+]
+mypy_path = [
+  "lib/spack",
+  "lib/spack/external",
+  "var/spack/repos",
+]
 allow_redefinition = true
 
 # This and a generated import file allows supporting packages
@@ -144,7 +152,7 @@ ignore_missing_imports = true
   ignore_missing_imports = false
 
   [[tool.mypy.overrides]]
-  module = 'packages.*'
+  module = 'spack_repo.*'
   ignore_errors = false
   ignore_missing_imports = false
   # we can't do this here, not a module scope option, in spack style instead
@@ -197,7 +205,7 @@ ignore_missing_imports = true
 useLibraryCodeForTypes = true
 reportMissingImports = true
 reportWildcardImportFromLibrary = false
-include = ['lib/spack', 'var/spack/repos']
+include = ['lib/spack', 'var/spack/repos', 'var/spack/test_repos']
 ignore = ['lib/spack/external']
 extraPaths = ['lib/spack', 'lib/spack/external']
 

share/spack/gitlab/cloud_pipelines/configs/win64/ci.yaml

@@ -5,7 +5,6 @@ ci:
       - Write-Output "Done"
 
       before_script::
-      - git config core.autocrlf true
       - fsutil 8dot3name set C:\ 0
       - . .\share\spack\setup-env.ps1
       - If (Test-Path -path C:\\key\intermediate_ci_signing_key.gpg) { spack.ps1 gpg trust C:\\key\intermediate_ci_signing_key.gpg }

share/spack/gitlab/cloud_pipelines/stacks/e4s-oneapi/spack.yaml

@@ -173,11 +173,11 @@ spack:
   - vtk-m ~openmp                   # +openmp: https://github.com/spack/spack/issues/31830
   - zfp
   # --
-  # - paraview +qt                  # llvm-17.0.6: https://github.com/spack/spack/issues/49625
-  # - py-cinemasci                  # llvm-14.0.6: https://github.com/spack/spack/issues/49625
-  # - visit                         # llvm-17.0.6: https://github.com/spack/spack/issues/49625
+  # - paraview +qt                  # concretize: paraview: Qt support requires GLX on non Windows; llvm-17.0.6: https://github.com/spack/spack/issues/49625
+  # - py-cinemasci                  # py-maturin-1.8.3: rust-lld: error: undefined symbol: _intel_fast_memcpy
+  # - visit                         # vtk-9.2.6: ??
   # --
-  # - chapel ~cuda ~rocm            # llvm-19.1.7: https://github.com/spack/spack/issues/49625
+  # - chapel ~cuda ~rocm            # chapel-2.4.0: KeyError: 'intel-oneapi-compilers': /builds/spack/spack/var/spack/repos/builtin/packages/chapel/package.py:602, in setup_chpl_compilers: env.set("CHPL_HOST_COMPILER", self.compiler_map[self.spec.compiler.name])
   # - cp2k +mpi                     # dbcsr-2.8.0: FAILED: src/CMakeFiles/dbcsr.dir/dbcsr_api.F-pp.f src/CMakeFiles/dbcsr.dir/dbcsr_api.F.o.ddi: 
   # - dealii                        # taskflow@3.7.0: cmake: Taskflow currently supports the following compilers: g++ v7.0 or above, clang++ v6.0 or above
   # - exago +mpi ~ipopt +hiop ~python +raja ^hiop+raja~sparse # raja-0.14.0: RAJA/pattern/kernel/Tile.hpp:174:30: error: no member named 'block_id' in 'IterableTiler<Iterable>'
@@ -185,8 +185,8 @@ spack:
   # - fftx                          # fftx-1.2.0: https://github.com/spack/spack/issues/49621
   # - fpm                           # fpm-0.10.0: /tmp/ifx1305151083OkWTRB/ifxqBG60i.i90: error #6405: The same named entity from different modules and/or program units cannot be referenced.   [TOML_TABLE]; fpm.F90(32048): error #7002: Error in opening the compiled module file.  Check INCLUDE paths.   [FPM_MANIFEST_PREPROCESS]
   # - geopm-runtime                 # concretize: c-blosc2: conflicts with '%oneapi';
-  # - glvis                         # llvm-17.0.6: https://github.com/spack/spack/issues/49625
-  # - gptune ~mpispawn              # llvm-14.0.6: https://github.com/spack/spack/issues/49625
+  - glvis                         # llvm-17.0.6: https://github.com/spack/spack/issues/49625
+  # - gptune ~mpispawn              # py-maturin-1.8.3: rust-lld: error: undefined symbol: __intel_cpu_feature_indicator_x
   # - lbann                         # lbann-0.104: https://github.com/spack/spack/issues/49619
   # - libpressio +bitgrooming +bzip2 ~cuda ~cusz +fpzip +hdf5 +libdistributed +lua +openmp +python +sz +sz3 +unix +zfp # concretize: c-blosc2: conflicts with '%oneapi';
   # - nek5000 +mpi ~visit           # nek5000-19.0: RuntimeError: Cannot build example: short_tests/eddy.
@@ -209,8 +209,8 @@ spack:
   # --
   # - py-jupyterlab                 # py-maturin: rust-lld: error: undefined symbol: _intel_fast_memcpy
   # - py-notebook                   # py-maturin: rust-lld: error: undefined symbol: _intel_fast_memcpy
-  # - py-numba                      # llvm-14.0.6: https://github.com/spack/spack/issues/49625
-  # - py-pandas                     # llvm-14.0.6: https://github.com/spack/spack/issues/49625
+  - py-numba                      # llvm-14.0.6: https://github.com/spack/spack/issues/49625
+  - py-pandas                     # llvm-14.0.6: https://github.com/spack/spack/issues/49625
   # - py-plotly                     # py-maturin: rust-lld: error: undefined symbol: _intel_fast_memcpy
 
   - aml +level_zero

share/spack/qa/run-unit-tests

@@ -40,7 +40,9 @@ spack -p --lines 20 spec mpileaks%gcc
 $coverage_run $(which spack) bootstrap status --dev --optional
 
 # Check that we can import Spack packages directly as a first import
-$coverage_run $(which spack) python -c "import spack.pkg.builtin.mpileaks; repr(spack.pkg.builtin.mpileaks.Mpileaks)"
+# TODO: this check is disabled, because sys.path is only updated once
+# spack.repo.PATH.get_pkg_class is called.
+# $coverage_run $(which spack) python -c "import spack.pkg.builtin.mpileaks; repr(spack.pkg.builtin.mpileaks.Mpileaks)"
 
 #-----------------------------------------------------------
 # Run unit tests with code coverage

var/spack/repos/builtin.mock/packages/compiler-wrapper

@@ -1 +0,0 @@
-../../builtin/packages/compiler-wrapper/

var/spack/repos/builtin.mock/packages/gcc-runtime

@@ -1 +0,0 @@
-../../builtin/packages/gcc-runtime

var/spack/repos/builtin/packages/amdblis/blis-4.0_gcc_clang_znver4.patch

@@ -1,55 +0,0 @@
-diff -Naur a/config/zen4/make_defs.mk b/config/zen4/make_defs.mk
---- a/config/zen4/make_defs.mk	2022-11-12 13:05:45.000000000 +0000
-+++ b/config/zen4/make_defs.mk	2023-05-12 14:40:10.848359434 +0000
-@@ -73,6 +73,15 @@
- 
- 
- # gcc 11.0 or later:
-+ifeq ($(shell test $(GCC_VERSION) -ge 13; echo $$?),0)
-+ifneq ($(DEBUG_TYPE),noopt)
-+CKOPTFLAGS     := -O2 -fgcse-after-reload -fipa-cp-clone -floop-interchange -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning -fsplit-loops -fsplit-paths -ftree-loop-distribution -funswitch-loops -fvect-cost-model=dynamic -fversion-loops-for-strides -fomit-frame-pointer
-+endif
-+
-+CKVECFLAGS     +=  -march=znver4 -mfpmath=sse
-+CRVECFLAGS     +=  -march=znver4
-+
-+else
- ifeq ($(shell test $(GCC_VERSION) -ge 11; echo $$?),0)
- # Update CKOPTFLAGS for gcc 11+ to use O3 optimization without
- # -ftree-partial-pre flag. This flag results in suboptimal code
-@@ -100,6 +109,7 @@
- endif # GCC 8
- endif # GCC 9
- endif # GCC 11
-+endif # GCC 13
- else
- ifeq ($(CC_VENDOR),clang)
- 
-@@ -132,6 +142,16 @@
- #if compiling with clang
- VENDOR_STRING := $(strip $(shell ${CC_VENDOR} --version | egrep -o '[0-9]+\.[0-9]+\.?[0-9]*'))
- CC_MAJOR := $(shell (echo ${VENDOR_STRING} | cut -d. -f1))
-+#clang 16 or later:
-+ifeq ($(shell test $(CC_MAJOR) -ge 16; echo $$?),0)
-+CKVECFLAGS += -march=znver4
-+CRVECFLAGS += -march=znver4
-+else
-+#clang 12 or later:
-+ifeq ($(shell test $(CC_MAJOR) -ge 12; echo $$?),0)
-+CKVECFLAGS += -march=znver3 -mavx512f -mavx512dq -mavx512bw -mavx512vl -mavx512vnni -mavx512bf16 -mfpmath=sse -falign-loops=64
-+CRVECFLAGS += -march=znver3
-+else
- #clang 9.0 or later:
- ifeq ($(shell test $(CC_MAJOR) -ge 9; echo $$?),0)
- CKVECFLAGS += -march=znver2
-@@ -139,7 +159,9 @@
- else
- CKVECFLAGS += -march=znver1
- CRVECFLAGS += -march=znver1
--endif # ge 9
-+endif # clang 9
-+endif # clang 12
-+endif # clang 16
- endif # aocc 2
- endif # aocc 3
- endif # aocc 4

var/spack/repos/builtin/packages/py-netcdf4/disable_parallel_support.patch

@@ -1,11 +0,0 @@
---- a/setup.py
-+++ b/setup.py
-@@ -392,7 +392,7 @@
-        (netcdf_lib_version > "4.4" and netcdf_lib_version < "4.5"):
-         has_cdf5_format = True
- 
--    has_parallel_support = check_has_parallel_support(inc_dirs)
-+    has_parallel_support = False
-     has_has_not = "has" if has_parallel_support else "does not have"
-     print(f"netcdf lib {has_has_not} parallel functions")
- 

var/spack/repos/compiler_runtime.test/packages/compiler-wrapper

@@ -1 +0,0 @@
-../../builtin/packages/compiler-wrapper/

var/spack/repos/flags.test/packages/compiler-wrapper

@@ -1 +0,0 @@
-../../builtin/packages/compiler-wrapper/

var/spack/repos/spack_repo/builtin/packages/_3dtk/package.py

@@ -21,6 +21,9 @@ class _3dtk(CMakePackage):
     version("trunk", svn="https://svn.code.sf.net/p/slam6d/code/trunk", preferred=True)
     version("1.2", svn="https://svn.code.sf.net/p/slam6d/code/branches/3dtk-release-1.2")
 
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
+
     variant("cgal", default=False, description="Compile with CGAL support")
     variant("opengl", default=True, description="Compile with OpenGL support")
     variant("opencv", default=True, description="Compile with OpenCV support")

var/spack/repos/spack_repo/builtin/packages/_global/package.py

@@ -11,12 +11,13 @@ class Global(Package):
     """The Gnu Global tagging system"""
 
     homepage = "https://www.gnu.org/software/global"
-    url = "http://tamacom.com/global/global-6.5.tar.gz"
+    url = "https://ftp.gnu.org/pub/gnu/global/global-6.5.tar.gz"
 
     maintainers("gaber")
 
     license("LGPL-3.0-only")
 
+    version("6.6.14", sha256="f6e7fd0b68aed292e85bb686616baf6551d5c9424adcddca11d808ba318cb320")
     version("6.6.7", sha256="69a0f77f53827c5568176c1d382166df361e74263a047f0b3058aa2f2ad58a3c")
     version("6.6.6", sha256="758078afff98d4c051c58785c7ada3ed1977fabb77f8897ff657b71cc62d4d5d")
     version("6.6.4", sha256="987e8cb956c53f8ebe4453b778a8fde2037b982613aba7f3e8e74bcd05312594")

var/spack/repos/spack_repo/builtin/packages/abyss/package.py

@@ -5,7 +5,8 @@
 import numbers
 
 from spack.package import *
-from spack.pkg.builtin.boost import Boost
+
+from ..boost.package import Boost
 
 
 def is_multiple_32(x):