Document how to handle changing build systems (#25174)
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Adam J. Stewart
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@ -63,6 +63,7 @@ on these ideas for each distinct build system that Spack supports:
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build_systems/intelpackage
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build_systems/rocmpackage
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build_systems/custompackage
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build_systems/multiplepackage
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For reference, the :py:mod:`Build System API docs <spack.build_systems>`
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provide a list of build systems and methods/attributes that can be
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350
lib/spack/docs/build_systems/multiplepackage.rst
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350
lib/spack/docs/build_systems/multiplepackage.rst
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@ -0,0 +1,350 @@
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.. Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
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Spack Project Developers. See the top-level COPYRIGHT file for details.
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SPDX-License-Identifier: (Apache-2.0 OR MIT)
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.. _multiplepackage:
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----------------------
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Multiple Build Systems
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----------------------
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Quite frequently, a package will change build systems from one version to the
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next. For example, a small project that once used a single Makefile to build
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may now require Autotools to handle the increased number of files that need to
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be compiled. Or, a package that once used Autotools may switch to CMake for
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Windows support. In this case, it becomes a bit more challenging to write a
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single build recipe for this package in Spack.
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There are several ways that this can be handled in Spack:
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#. Subclass the new build system, and override phases as needed (preferred)
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#. Subclass ``Package`` and implement ``install`` as needed
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#. Create separate ``*-cmake``, ``*-autotools``, etc. packages for each build system
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#. Rename the old package to ``*-legacy`` and create a new package
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#. Move the old package to a ``legacy`` repository and create a new package
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#. Drop older versions that only support the older build system
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Of these options, 1 is preferred, and will be demonstrated in this
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documentation. Options 3-5 have issues with concretization, so shouldn't be
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used. Options 4-5 also don't support more than two build systems. Option 6 only
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works if the old versions are no longer needed. Option 1 is preferred over 2
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because it makes it easier to drop the old build system entirely.
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The exact syntax of the package depends on which build systems you need to
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support. Below are a couple of common examples.
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^^^^^^^^^^^^^^^^^^^^^
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Makefile -> Autotools
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^^^^^^^^^^^^^^^^^^^^^
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Let's say we have the following package:
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.. code-block:: python
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class Foo(MakefilePackage):
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version("1.2.0", sha256="...")
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def edit(self, spec, prefix):
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filter_file("CC=", "CC=" + spack_cc, "Makefile")
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def install(self, spec, prefix):
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install_tree(".", prefix)
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The package subclasses from :ref:`makefilepackage`, which has three phases:
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#. ``edit`` (does nothing by default)
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#. ``build`` (runs ``make`` by default)
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#. ``install`` (runs ``make install`` by default)
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In this case, the ``install`` phase needed to be overridden because the
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Makefile did not have an install target. We also modify the Makefile to use
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Spack's compiler wrappers. The default ``build`` phase is not changed.
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Starting with version 1.3.0, we want to use Autotools to build instead.
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:ref:`autotoolspackage` has four phases:
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#. ``autoreconf`` (does not if a configure script already exists)
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#. ``configure`` (runs ``./configure --prefix=...`` by default)
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#. ``build`` (runs ``make`` by default)
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#. ``install`` (runs ``make install`` by default)
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If the only version we need to support is 1.3.0, the package would look as
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simple as:
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.. code-block:: python
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class Foo(AutotoolsPackage):
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version("1.3.0", sha256="...")
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def configure_args(self):
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return ["--enable-shared"]
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In this case, we use the default methods for each phase and only override
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``configure_args`` to specify additional flags to pass to ``./configure``.
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If we wanted to write a single package that supports both versions 1.2.0 and
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1.3.0, it would look something like:
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.. code-block:: python
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class Foo(AutotoolsPackage):
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version("1.3.0", sha256="...")
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version("1.2.0", sha256="...", deprecated=True)
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def configure_args(self):
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return ["--enable-shared"]
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# Remove the following once version 1.2.0 is dropped
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@when("@:1.2")
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def patch(self):
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filter_file("CC=", "CC=" + spack_cc, "Makefile")
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@when("@:1.2")
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def autoreconf(self, spec, prefix):
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pass
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@when("@:1.2")
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def configure(self, spec, prefix):
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pass
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@when("@:1.2")
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def install(self, spec, prefix):
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install_tree(".", prefix)
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There are a few interesting things to note here:
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* We added ``deprecated=True`` to version 1.2.0. This signifies that version
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1.2.0 is deprecated and shouldn't be used. However, if a user still relies
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on version 1.2.0, it's still there and builds just fine.
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* We moved the contents of the ``edit`` phase to the ``patch`` function. Since
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``AutotoolsPackage`` doesn't have an ``edit`` phase, the only way for this
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step to be executed is to move it to the ``patch`` function, which always
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gets run.
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* The ``autoreconf`` and ``configure`` phases become no-ops. Since the old
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Makefile-based build system doesn't use these, we ignore these phases when
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building ``foo@1.2.0``.
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* The ``@when`` decorator is used to override these phases only for older
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versions. The default methods are used for ``foo@1.3:``.
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Once a new Spack release comes out, version 1.2.0 and everything below the
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comment can be safely deleted. The result is the same as if we had written a
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package for version 1.3.0 from scratch.
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^^^^^^^^^^^^^^^^^^
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Autotools -> CMake
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^^^^^^^^^^^^^^^^^^
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Let's say we have the following package:
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.. code-block:: python
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class Bar(AutotoolsPackage):
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version("1.2.0", sha256="...")
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def configure_args(self):
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return ["--enable-shared"]
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The package subclasses from :ref:`autotoolspackage`, which has four phases:
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#. ``autoreconf`` (does not if a configure script already exists)
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#. ``configure`` (runs ``./configure --prefix=...`` by default)
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#. ``build`` (runs ``make`` by default)
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#. ``install`` (runs ``make install`` by default)
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In this case, we use the default methods for each phase and only override
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``configure_args`` to specify additional flags to pass to ``./configure``.
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Starting with version 1.3.0, we want to use CMake to build instead.
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:ref:`cmakepackage` has three phases:
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#. ``cmake`` (runs ``cmake ...`` by default)
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#. ``build`` (runs ``make`` by default)
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#. ``install`` (runs ``make install`` by default)
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If the only version we need to support is 1.3.0, the package would look as
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simple as:
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.. code-block:: python
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class Bar(CMakePackage):
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version("1.3.0", sha256="...")
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def cmake_args(self):
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return [self.define("BUILD_SHARED_LIBS", True)]
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In this case, we use the default methods for each phase and only override
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``cmake_args`` to specify additional flags to pass to ``cmake``.
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If we wanted to write a single package that supports both versions 1.2.0 and
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1.3.0, it would look something like:
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.. code-block:: python
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class Bar(CMakePackage):
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version("1.3.0", sha256="...")
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version("1.2.0", sha256="...", deprecated=True)
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def cmake_args(self):
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return [self.define("BUILD_SHARED_LIBS", True)]
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# Remove the following once version 1.2.0 is dropped
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def configure_args(self):
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return ["--enable-shared"]
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@when("@:1.2")
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def cmake(self, spec, prefix):
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configure("--prefix=" + prefix, *self.configure_args())
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There are a few interesting things to note here:
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* We added ``deprecated=True`` to version 1.2.0. This signifies that version
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1.2.0 is deprecated and shouldn't be used. However, if a user still relies
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on version 1.2.0, it's still there and builds just fine.
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* Since CMake and Autotools are so similar, we only need to override the
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``cmake`` phase, we can use the default ``build`` and ``install`` phases.
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* We override ``cmake`` to run ``./configure`` for older versions.
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``configure_args`` remains the same.
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* The ``@when`` decorator is used to override these phases only for older
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versions. The default methods are used for ``bar@1.3:``.
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Once a new Spack release comes out, version 1.2.0 and everything below the
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comment can be safely deleted. The result is the same as if we had written a
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package for version 1.3.0 from scratch.
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Multiple build systems for the same version
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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During the transition from one build system to another, developers often
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support multiple build systems at the same time. Spack can only use a single
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build system for a single version. To decide which build system to use for a
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particular version, take the following things into account:
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1. If the developers explicitly state that one build system is preferred over
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another, use that one.
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2. If one build system is considered "experimental" while another is considered
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"stable", use the stable build system.
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3. Otherwise, use the newer build system.
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The developer preference for which build system to use can change over time as
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a newer build system becomes stable/recommended.
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Dropping support for old build systems
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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When older versions of a package don't support a newer build system, it can be
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tempting to simply delete them from a package. This significantly reduces
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package complexity and makes the build recipe much easier to maintain. However,
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other packages or Spack users may rely on these older versions. The recommended
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approach is to first support both build systems (as demonstrated above),
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:ref:`deprecate <deprecate>` versions that rely on the old build system, and
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remove those versions and any phases that needed to be overridden in the next
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Spack release.
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Three or more build systems
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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In rare cases, a package may change build systems multiple times. For example,
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a package may start with Makefiles, then switch to Autotools, then switch to
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CMake. The same logic used above can be extended to any number of build systems.
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For example:
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.. code-block:: python
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class Baz(CMakePackage):
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version("1.4.0", sha256="...") # CMake
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version("1.3.0", sha256="...") # Autotools
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version("1.2.0", sha256="...") # Makefile
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def cmake_args(self):
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return [self.define("BUILD_SHARED_LIBS", True)]
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# Remove the following once version 1.3.0 is dropped
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def configure_args(self):
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return ["--enable-shared"]
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@when("@1.3")
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def cmake(self, spec, prefix):
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configure("--prefix=" + prefix, *self.configure_args())
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# Remove the following once version 1.2.0 is dropped
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@when("@:1.2")
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def patch(self):
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filter_file("CC=", "CC=" + spack_cc, "Makefile")
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@when("@:1.2")
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def cmake(self, spec, prefix):
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pass
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@when("@:1.2")
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def install(self, spec, prefix):
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install_tree(".", prefix)
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^^^^^^^^^^^^^^^^^^^
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Additional examples
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^^^^^^^^^^^^^^^^^^^
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When writing new packages, it often helps to see examples of existing packages.
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Here is an incomplete list of existing Spack packages that have changed build
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systems before:
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================ ===================== ================
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Package Previous Build System New Build System
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================ ===================== ================
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amber custom CMake
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arpack-ng Autotools CMake
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atk Autotools Meson
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blast None Autotools
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dyninst Autotools CMake
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evtgen Autotools CMake
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fish Autotools CMake
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gdk-pixbuf Autotools Meson
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glib Autotools Meson
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glog Autotools CMake
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gmt Autotools CMake
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gtkplus Autotools Meson
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hpl Makefile Autotools
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interproscan Perl Maven
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jasper Autotools CMake
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kahip SCons CMake
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kokkos Makefile CMake
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kokkos-kernels Makefile CMake
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leveldb Makefile CMake
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libdrm Autotools Meson
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libjpeg-turbo Autotools CMake
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mesa Autotools Meson
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metis None CMake
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mpifileutils Autotools CMake
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muparser Autotools CMake
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mxnet Makefile CMake
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nest Autotools CMake
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neuron Autotools CMake
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nsimd CMake nsconfig
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opennurbs Makefile CMake
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optional-lite None CMake
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plasma Makefile CMake
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preseq Makefile Autotools
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protobuf Autotools CMake
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py-pygobject Autotools Python
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singularity Autotools Makefile
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span-lite None CMake
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ssht Makefile CMake
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string-view-lite None CMake
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superlu Makefile CMake
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superlu-dist Makefile CMake
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uncrustify Autotools CMake
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================ ===================== ================
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Packages that support multiple build systems can be a bit confusing to write.
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Don't hesitate to open an issue or draft pull request and ask for advice from
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other Spack developers!
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@ -612,6 +612,7 @@ it executable, then runs it with some arguments.
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installer = Executable(self.stage.archive_file)
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installer('--prefix=%s' % prefix, 'arg1', 'arg2', 'etc.')
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.. _deprecate:
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^^^^^^^^^^^^^^^^^^^^^^^^
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Deprecating old versions
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