Add a PEP517 interface

pep517 defines a new module method of specifying build backends.
To allow pbr to exist in this world, we should define the interface
that's needed. For this to be used, one will put:

  [build-system]
  requires = ["pbr>=5.7.0", "setuptools>=36.6.0", "wheel"]
  build-backend = "pbr.build"

Into pyproject.toml - and the pep517 interface will be used.

This doesn't really change anything else - it just makes us support this.
So by itself this commit isn't SUPER helpful. But maybe let's take baby
steps with something this prone to strife, yeah?

After this we can start teasing some things apart and doing our
own things directly.

Co-Authored-By: Clark Boylan <clark.boylan@gmail.com>
Change-Id: I293f59b5074a38c78adffe580de2f1533bb01ce7

doc/source/user/using.rst

@@ -34,6 +34,18 @@ something like this::
    While one can pass any arguments supported by setuptools to ``setup()``,
    any conflicting arguments supplied in ``setup.cfg`` will take precedence.
 
+``pyproject.toml``
+------------------
+
+As an alternative to writing a ``setup.py`` you can instead setup PBR
+through the PEP 517 build-system configuration in ``pyproject.toml``.
+Your build-system block in ``pyproject.toml`` will need to look something
+like this::
+
+    [build-system]
+    requires = ["pbr>=5.7.0", "setuptools>=36.6.0", "wheel"]
+    build-backend = "pbr.build"
+
 .. _setup_cfg:
 
 ``setup.cfg``

pbr/build.py

@@ -0,0 +1,61 @@
+# Copyright 2021 Monty Taylor
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+"""pep-517 support
+
+Add::
+
+      [build-system]
+      requires = ["pbr>=5.7.0", "setuptools>=36.6.0", "wheel"]
+      build-backend = "pbr.build"
+
+to pyproject.toml to use this
+"""
+
+from setuptools import build_meta
+
+__all__ = [
+    'get_requires_for_build_sdist',
+    'get_requires_for_build_wheel',
+    'prepare_metadata_for_build_wheel',
+    'build_wheel',
+    'build_sdist',
+]
+
+
+def get_requires_for_build_wheel(config_settings=None):
+    return build_meta.get_requires_for_build_wheel(config_settings)
+
+
+def get_requires_for_build_sdist(config_settings=None):
+    return build_meta.get_requires_for_build_sdist(config_settings)
+
+
+def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
+    return build_meta.prepare_metadata_for_build_wheel(
+        metadata_directory, config_settings)
+
+
+def build_wheel(
+    wheel_directory,
+    config_settings=None,
+    metadata_directory=None,
+):
+    return build_meta.build_wheel(
+        wheel_directory, config_settings, metadata_directory,
+    )
+
+
+def build_sdist(sdist_directory, config_settings=None):
+    return build_meta.build_sdist(sdist_directory, config_settings)

pbr/tests/test_packaging.py

@@ -172,7 +172,7 @@ class Venv(fixtures.Fixture):
         """
         self._reason = reason
         if modules == ():
-            modules = ['pip', 'wheel', PBR_ROOT]
+            modules = ['pip', 'wheel', 'build', PBR_ROOT]
         self.modules = modules
         if pip_cmd is None:
             self.pip_cmd = ['-m', 'pip', '-v', 'install']
@@ -922,6 +922,56 @@ class TestRequirementParsing(base.BaseTestCase):
             self.assertEqual(exp_parsed, gen_parsed)
 
 
+class TestPEP517Support(base.BaseTestCase):
+    def test_pep_517_support(self):
+        pkgs = {
+            'test_pep517':
+                {
+                    'requirements.txt': textwrap.dedent("""\
+                        sphinx
+                        iso8601
+                    """),
+                    # Override no setup.py.
+                    'setup.py': '',
+                    'setup.cfg': textwrap.dedent("""\
+                        [metadata]
+                        name = test_pep517
+                        summary = A tiny test project
+                        author = PBR Team
+                        author-email = foo@example.com
+                        home-page = https://example.com/
+                        classifier =
+                            Intended Audience :: Information Technology
+                            Intended Audience :: System Administrators
+                            License :: OSI Approved :: Apache Software License
+                            Operating System :: POSIX :: Linux
+                            Programming Language :: Python
+                            Programming Language :: Python :: 2
+                            Programming Language :: Python :: 2.7
+                            Programming Language :: Python :: 3
+                            Programming Language :: Python :: 3.6
+                            Programming Language :: Python :: 3.7
+                            Programming Language :: Python :: 3.8
+                    """),
+                    'pyproject.toml': textwrap.dedent("""\
+                        [build-system]
+                        requires = ["pbr", "setuptools>=36.6.0", "wheel"]
+                        build-backend = "pbr.build"
+                    """)},
+        }
+        pkg_dirs = self.useFixture(CreatePackages(pkgs)).package_dirs
+        pkg_dir = pkg_dirs['test_pep517']
+        venv = self.useFixture(Venv('PEP517'))
+
+        # Test building sdists and wheels works. Note we do not use pip here
+        # because pip will forcefully install the latest version of PBR on
+        # pypi to satisfy the build-system requires. This means we can't self
+        # test changes using pip. Build with --no-isolation appears to avoid
+        # this problem.
+        self._run_cmd(venv.python, ('-m', 'build', '--no-isolation', '.'),
+                      allow_fail=False, cwd=pkg_dir)
+
+
 class TestRepositoryURLDependencies(base.BaseTestCase):
 
     def setUp(self):

pyproject.toml.future

@@ -0,0 +1,9 @@
+# PBR doesn't use the pyproject.toml interface internally yet as
+# fixing issues in the system will be difficult if PBR itself
+# depends on it. We will put this file into place at pyproject.toml
+# once we are more confident it works generally.
+
+[build-system]
+requires = ["setuptools>=36.6.0", "wheel"]
+build-backend = "pbr.build"
+backend-path = ["."]

releasenotes/notes/pep517-support-89189ce0bab15845.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    PBR now includes a PEP 517 build-backend and can be used in
+    pyproject.toml build-system configuration. Setuptools continues
+    to be the underlying mechanism with PBR acting as a driver via
+    PEP 517 entrypoints.