Allow for packages with multiple build-systems (#30738)

This commit extends the DSL that can be used in packages
to allow declaring that a package uses different build-systems
under different conditions.

It requires each spec to have a `build_system` single valued
variant. The variant can be used in many context to query, manipulate
or select the build system associated with a concrete spec.

The knowledge to build a package has been moved out of the
PackageBase hierarchy, into a new Builder hierarchy. Customization
of the default behavior for a given builder can be obtained by
coding a new derived builder in package.py.

The "run_after" and "run_before" decorators are now applied to
methods on the builder. They can also incorporate a "when="
argument to specify that a method is run only when certain
conditions apply.

For packages that do not define their own builder, forwarding logic
is added between the builder and package (methods not found in one
will be retrieved from the other); this PR is expected to be fully
backwards compatible with unmodified packages that use a single
build system.

1 files changed, 40 insertions, 37 deletions

diff --git a/lib/spack/spack/build_systems/qmake.py b/lib/spack/spack/build_systems/qmake.py
index c2af684592..f18bd9812f 100644
--- a/lib/spack/spack/build_systems/qmake.py
+++ b/lib/spack/spack/build_systems/qmake.py
@@ -2,82 +2,85 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-
 import inspect
 
 from llnl.util.filesystem import working_dir
 
-from spack.directives import depends_on
-from spack.package_base import PackageBase, run_after
+import spack.builder
+import spack.package_base
+from spack.directives import build_system, depends_on
+
+from ._checks import BaseBuilder, execute_build_time_tests
 
 
-class QMakePackage(PackageBase):
+class QMakePackage(spack.package_base.PackageBase):
     """Specialized class for packages built using qmake.
 
     For more information on the qmake build system, see:
     http://doc.qt.io/qt-5/qmake-manual.html
+    """
+
+    #: This attribute is used in UI queries that need to know the build
+    #: system base class
+    build_system_class = "QMakePackage"
+    #: Legacy buildsystem attribute used to deserialize and install old specs
+    legacy_buildsystem = "qmake"
+
+    build_system("qmake")
+
+    depends_on("qt", type="build", when="build_system=qmake")
+
 
-    This class provides three phases that can be overridden:
+@spack.builder.builder("qmake")
+class QMakeBuilder(BaseBuilder):
+    """The qmake builder provides three phases that can be overridden:
 
-    1. :py:meth:`~.QMakePackage.qmake`
-    2. :py:meth:`~.QMakePackage.build`
-    3. :py:meth:`~.QMakePackage.install`
+    1. :py:meth:`~.QMakeBuilder.qmake`
+    2. :py:meth:`~.QMakeBuilder.build`
+    3. :py:meth:`~.QMakeBuilder.install`
 
     They all have sensible defaults and for many packages the only thing
-    necessary will be to override :py:meth:`~.QMakePackage.qmake_args`.
+    necessary will be to override :py:meth:`~.QMakeBuilder.qmake_args`.
     """
 
-    #: Phases of a qmake package
-    phases = ["qmake", "build", "install"]
+    phases = ("qmake", "build", "install")
 
-    #: This attribute is used in UI queries that need to know the build
-    #: system base class
-    build_system_class = "QMakePackage"
+    #: Names associated with package methods in the old build-system format
+    legacy_methods = ("qmake_args", "check")
+
+    #: Names associated with package attributes in the old build-system format
+    legacy_attributes = ("build_directory", "build_time_test_callbacks")
 
     #: Callback names for build-time test
     build_time_test_callbacks = ["check"]
 
-    depends_on("qt", type="build")
-
     @property
     def build_directory(self):
         """The directory containing the ``*.pro`` file."""
         return self.stage.source_path
 
     def qmake_args(self):
-        """Produces a list containing all the arguments that must be passed to
-        qmake
-        """
+        """List of arguments passed to qmake."""
         return []
 
-    def qmake(self, spec, prefix):
+    def qmake(self, pkg, spec, prefix):
         """Run ``qmake`` to configure the project and generate a Makefile."""
-
         with working_dir(self.build_directory):
-            inspect.getmodule(self).qmake(*self.qmake_args())
+            inspect.getmodule(self.pkg).qmake(*self.qmake_args())
 
-    def build(self, spec, prefix):
+    def build(self, pkg, spec, prefix):
         """Make the build targets"""
-
         with working_dir(self.build_directory):
-            inspect.getmodule(self).make()
+            inspect.getmodule(self.pkg).make()
 
-    def install(self, spec, prefix):
+    def install(self, pkg, spec, prefix):
         """Make the install targets"""
-
         with working_dir(self.build_directory):
-            inspect.getmodule(self).make("install")
-
-    # Tests
+            inspect.getmodule(self.pkg).make("install")
 
     def check(self):
-        """Searches the Makefile for a ``check:`` target and runs it if found."""
-
+        """Search the Makefile for a ``check:`` target and runs it if found."""
         with working_dir(self.build_directory):
             self._if_make_target_execute("check")
 
-    run_after("build")(PackageBase._run_default_build_time_test_callbacks)
-
-    # Check that self.prefix is there after installation
-    run_after("install")(PackageBase.sanity_check_prefix)
+    spack.builder.run_after("build")(execute_build_time_tests)