Docs/Packaging guide: Add BundlePackage (#39691)

* Docs/Packaging guide: Add BundlePackage
* Adjusted version ordering note to reflect convention.

lib/spack/docs/build_systems/bundlepackage.rst

@@ -9,9 +9,32 @@
 Bundle
 ------
 
-``BundlePackage`` represents a set of packages that are expected to work well
+``BundlePackage`` represents a set of packages that are expected to work
-together, such as a collection of commonly used software libraries.  The
+well together, such as a collection of commonly used software libraries.
-associated software is specified as bundle dependencies.
+The associated software is specified as dependencies.
+
+If it makes sense, variants, conflicts, and requirements can be added to
+the package. :ref:`Variants <variants>` ensure that common build options
+are consistent across the packages supporting them.  :ref:`Conflicts
+and requirements <packaging_conflicts>` prevent attempts to build with known
+bugs or limitations.
+
+For example, if ``MyBundlePackage`` is known to only build on ``linux``,
+it could use the ``require`` directive as follows:
+
+.. code-block:: python
+
+    require("platform=linux", msg="MyBundlePackage only builds on linux")
+
+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>`_
+
+where ``Xsdk`` also inherits from ``CudaPackage`` and ``RocmPackage`` and
+``Libc`` is a virtual bundle package for the C standard library.
 
 
 ^^^^^^^^

lib/spack/docs/packaging_guide.rst

@@ -363,6 +363,42 @@ one of these::
 If Spack finds none of these variables set, it will look for ``vim``, ``vi``, ``emacs``,
 ``nano``, and ``notepad``, in that order.
 
+^^^^^^^^^^^^^^^^^
+Bundling software
+^^^^^^^^^^^^^^^^^
+
+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>`_).
+
+These versioned packages primarily consist of dependencies on the associated
+software packages. They can include :ref:`variants <variants>` to ensure
+common build options are consistently applied to dependencies. Known build
+failures, such as not building on a platform or when certain compilers or
+variants are used, can be flagged with :ref:`conflicts <packaging_conflicts>`.
+Build requirements, such as only building with specific compilers, can similarly
+be flagged with :ref:`requires <packaging_conflicts>`.
+
+The ``spack create --template bundle`` command will create a skeleton
+``BundlePackage`` ``package.py`` for you:
+
+.. code-block:: console
+
+   $ spack create --template bundle --name coolsdk
+
+Now you can fill in the basic package documentation, version(s), and software
+package dependencies along with any other relevant customizations.
+
+.. note::
+
+   Remember that bundle packages have no software of their own so there
+   is nothing to download.
+
+
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 Non-downloadable software
 ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -610,7 +646,16 @@ add a line like this in the package class:
        version("8.2.0", md5="1c9f62f0778697a09d36121ead88e08e")
        version("8.1.2", md5="d47dd09ed7ae6e7fd6f9a816d7f5fdf6")
 
-Versions should be listed in descending order, from newest to oldest.
+.. note::
+
+   By convention, we list versions in descending order, from newest to oldest.
+
+.. note::
+
+   :ref:`Bundle packages  <bundlepackage>` do not have source code so
+   there is nothing to fetch. Consequently, their version directives
+   consist solely of the version name (e.g., ``version("202309")``).
+
 
 ^^^^^^^^^^^^^
 Date Versions
@@ -2678,7 +2723,7 @@ Conflicts and requirements
 --------------------------
 
 Sometimes packages have known bugs, or limitations, that would prevent them
-to build e.g. against other dependencies or with certain compilers. Spack
+from building e.g. against other dependencies or with certain compilers. Spack
 makes it possible to express such constraints with the ``conflicts`` directive.
 
 Adding the following to a package:
@@ -5246,8 +5291,8 @@ Saving build-time files
     We highly recommend re-using build-time test sources and pared down
     input files for testing installed software. These files are easier
     to keep synchronized with software capabilities since they reside
-    within the software's repository. 
+    within the software's repository.
-    
+
     If that is not possible, you can add test-related files to the package
     repository (see :ref:`adding custom files <cache_custom_files>`). It
     will be important to maintain them so they work across listed or supported
@@ -5268,7 +5313,7 @@ where each argument has the following meaning:
 * ``pkg`` is an instance of the package for the spec under test.
 
 * ``srcs`` is a string *or* a list of strings corresponding to the
-  paths of subdirectories and or files needed for stand-alone testing. 
+  paths of subdirectories and or files needed for stand-alone testing.
 
 The paths must be relative to the staged source directory. Contents of
 subdirectories and files are copied to a special test cache subdirectory
@@ -5411,7 +5456,7 @@ Reading expected output from a file
 
 The helper function ``get_escaped_text_output`` is available for packages
 to retrieve and properly format the text from a file that contains the
-expected output from running an executable that may contain special 
+expected output from running an executable that may contain special
 characters.
 
 The signature for ``get_escaped_text_output`` is:
@@ -5458,7 +5503,7 @@ source code, the path would be obtained as shown below.
            db_filename = test_cache_dir.join("packages.db")
 
 Alternatively, if the file was copied to the ``share/tests`` subdirectory
-as part of the installation process, the test could access the path as 
+as part of the installation process, the test could access the path as
 follows:
 
 .. code-block:: python
@@ -5555,7 +5600,7 @@ Inheriting stand-alone tests
 Stand-alone tests defined in parent (.e.g., :ref:`build-systems`) and
 virtual (e.g., :ref:`virtual-dependencies`) packages are executed by
 packages that inherit from or provide interface implementations for those
-packages, respectively. 
+packages, respectively.
 
 The table below summarizes the stand-alone tests that will be executed along
 with those implemented in the package itself.
@@ -5625,7 +5670,7 @@ for ``openmpi``:
    SKIPPED: test_version_oshcc: oshcc is not installed
    ...
    ==> [2023-03-10-16:04:02.215227] Completed testing
-   ==> [2023-03-10-16:04:02.215597] 
+   ==> [2023-03-10-16:04:02.215597]
    ======================== SUMMARY: openmpi-4.1.4-ubmrigj ========================
    Openmpi::test_bin_mpirun .. PASSED
    Openmpi::test_bin_ompi_info .. PASSED