Allow building wheels in %pyproject_buildrequires to support other build backends

The hook is optional, see https://www.python.org/dev/peps/pep-0517/#prepare-metadata-for-build-wheel

> If a build frontend needs this information and the method is not defined,
> it should call build_wheel and look at the resulting metadata directly.

This is not yet automatically detected because the feature is provisional.
Use `%pyproject_buildrequires -w` to opt-in.

Resolves: rhbz#2060109

README.md

@@ -69,8 +69,7 @@ the package's runtime dependencies need to also be included as build requirement
 
 Hence, `%pyproject_buildrequires` also generates runtime dependencies by default.
 
-For this to work, the project's build system must support the
+For this to work, the project's build system must support the [`prepare-metadata-for-build-wheel` hook].
-[`prepare-metadata-for-build-wheel` hook](https://www.python.org/dev/peps/pep-0517/#prepare-metadata-for-build-wheel).
 The popular buildsystems (setuptools, flit, poetry) do support it.
 
 This behavior can be disabled
@@ -80,6 +79,28 @@ using the `-R` flag:
     %generate_buildrequires
     %pyproject_buildrequires -R
 
+Alternatively, the runtime dependencies can be obtained by building the wheel and reading the metadata from the built wheel.
+This can be enabled by using the `-w` flag.
+Support for building wheels with `%pyproject_buildrequires -w` is **provisional** and the behavior might change.
+Please subscribe to Fedora's [python-devel list] if you use the option.
+
+    %generate_buildrequires
+    %pyproject_buildrequires -w
+
+When this is used, the wheel is going to be built at least twice,
+becasue the `%generate_buildrequires` section runs repeatedly.
+To avoid accidentally reusing a wheel leaking from a previous (different) build,
+it cannot be reused between `%generate_buildrequires` rounds.
+Contrarily to that, rebuilding the wheel again in the `%build` section is redundant
+and the packager can omit the `%build` section entirely
+to reuse the wheel built from the last round of `%generate_buildrequires`.
+Be extra careful when attempting to modify the sources after `%pyproject_buildrequires`,
+e.g. when running extra commands in the `%build` section:
+
+    %build
+    cython src/wrong.pyx  # this is too late with %%pyproject_buildrequires -w
+    %pyproject_wheel
+
 For projects that specify test requirements using an [`extra`
 provide](https://packaging.python.org/specifications/core-metadata/#provides-extra-multiple-use),
 these can be added using the `-x` flag.
@@ -121,9 +142,12 @@ in worst case, patch/sed the requirement out from the tox configuration.
 
 Note that both `-x` and `-t` imply `-r`,
 because runtime dependencies are always required for testing.
+You can only use those options if the build backend  supports the [`prepare-metadata-for-build-wheel` hook],
+or together with `-w`.
 
 [tox]: https://tox.readthedocs.io/
 [tox-current-env]: https://github.com/fedora-python/tox-current-env/
+[`prepare-metadata-for-build-wheel` hook]: https://www.python.org/dev/peps/pep-0517/#prepare-metadata-for-build-wheel
 
 Additionally to generated requirements you can supply multiple file names to `%pyproject_buildrequires` macro.
 Dependencies will be loaded from them:
@@ -133,7 +157,7 @@ Dependencies will be loaded from them:
 For packages not using build system you can use `-N` to entirely skip automatical
 generation of requirements and install requirements only from manually specified files.
 `-N` option cannot be used in combination with other options mentioned above
-(`-r`, `-e`, `-t`, `-x`).
+(`-r`, `-w`, `-e`, `-t`, `-x`).
 
 Running tox based tests
 -----------------------

macros.pyproject

@@ -29,7 +29,7 @@
 %_set_pytest_addopts
 mkdir -p "%{_pyproject_builddir}"
 CFLAGS="${CFLAGS:-${RPM_OPT_FLAGS}}" LDFLAGS="${LDFLAGS:-${RPM_LD_FLAGS}}" TMPDIR="%{_pyproject_builddir}" \\\
-%{__python3} -m pip wheel --wheel-dir %{_pyproject_wheeldir} --no-deps --use-pep517 --no-build-isolation --disable-pip-version-check --no-clean --progress-bar off --verbose .
+%{__python3} -Bs %{_rpmconfigdir}/redhat/pyproject_wheel.py %{_pyproject_wheeldir}
 }
 
 
@@ -121,13 +121,21 @@ fi
 %toxenv %{default_toxenv}
 
 
-%pyproject_buildrequires(rRxtNe:) %{expand:\\\
+%pyproject_buildrequires(rRxtNwe:) %{expand:\\\
-%{-R:%{-r:%{error:The -R and -r options are mutually exclusive}}}
+%_set_pytest_addopts
+# The _auto_set_build_flags feature does not do this in %%generate_buildrequires section,
+# but we want to get an environment consistent with %%build:
+%{?_auto_set_build_flags:%set_build_flags}
+%{-R:
+%{-r:%{error:The -R and -r options are mutually exclusive}}
+%{-w:%{error:The -R and -w options are mutually exclusive}}
+}
 %{-N:
 %{-r:%{error:The -N and -r options are mutually exclusive}}
 %{-x:%{error:The -N and -x options are mutually exclusive}}
 %{-e:%{error:The -N and -e options are mutually exclusive}}
 %{-t:%{error:The -N and -t options are mutually exclusive}}
+%{-w:%{error:The -N and -w options are mutually exclusive}}
 }
 %{-e:%{expand:%global toxenv %(%{__python3} -s %{_rpmconfigdir}/redhat/pyproject_construct_toxenv.py %{?**})}}
 echo 'pyproject-rpm-macros'  # we already have this installed, but this way, it's repoqueryable
@@ -147,7 +155,9 @@ fi}
 # setuptools assumes no pre-existing dist-info
 rm -rfv *.dist-info/ >&2
 if [ -f %{__python3} ]; then
-  RPM_TOXENV="%{toxenv}" HOSTNAME="rpmbuild" %{__python3} -s %{_rpmconfigdir}/redhat/pyproject_buildrequires.py %{?!_python_no_extras_requires:--generate-extras} --python3_pkgversion %{python3_pkgversion} %{?**}
+  mkdir -p "%{_pyproject_builddir}"
+  CFLAGS="${CFLAGS:-${RPM_OPT_FLAGS}}" LDFLAGS="${LDFLAGS:-${RPM_LD_FLAGS}}" TMPDIR="%{_pyproject_builddir}" \\\
+  RPM_TOXENV="%{toxenv}" HOSTNAME="rpmbuild" %{__python3} -Bs %{_rpmconfigdir}/redhat/pyproject_buildrequires.py %{?!_python_no_extras_requires:--generate-extras} --python3_pkgversion %{python3_pkgversion} --wheeldir %{_pyproject_wheeldir} %{?**}
 fi
 }
 

pyproject-rpm-macros.spec

@@ -12,7 +12,7 @@ License:        MIT
 #   Increment Y and reset Z when new macros or features are added
 #   Increment Z when this is a bugfix or a cosmetic change
 # Dropping support for EOL Fedoras is *not* considered a breaking change
-Version:        1.1.0
+Version:        1.2.0
 Release:        1%{?dist}
 
 # Macro files
@@ -25,6 +25,7 @@ Source103:      pyproject_convert.py
 Source104:      pyproject_preprocess_record.py
 Source105:      pyproject_construct_toxenv.py
 Source106:      pyproject_requirements_txt.py
+Source107:      pyproject_wheel.py
 
 # Tests
 Source201:      test_pyproject_buildrequires.py
@@ -99,6 +100,7 @@ install -m 644 pyproject_save_files.py  %{buildroot}%{_rpmconfigdir}/redhat/
 install -m 644 pyproject_preprocess_record.py %{buildroot}%{_rpmconfigdir}/redhat/
 install -m 644 pyproject_construct_toxenv.py %{buildroot}%{_rpmconfigdir}/redhat/
 install -m 644 pyproject_requirements_txt.py %{buildroot}%{_rpmconfigdir}/redhat/
+install -m 644 pyproject_wheel.py %{buildroot}%{_rpmconfigdir}/redhat/
 
 %if %{with tests}
 %check
@@ -118,11 +120,18 @@ export HOSTNAME="rpmbuild"  # to speedup tox in network-less mock, see rhbz#1856
 %{_rpmconfigdir}/redhat/pyproject_preprocess_record.py
 %{_rpmconfigdir}/redhat/pyproject_construct_toxenv.py
 %{_rpmconfigdir}/redhat/pyproject_requirements_txt.py
+%{_rpmconfigdir}/redhat/pyproject_wheel.py
 
 %doc README.md
 %license LICENSE
 
 %changelog
+* Wed Apr 27 2022 Miro Hrončok <mhroncok@redhat.com> - 1.2.0-1
+- %%pyproject_buildrequires: Add provisional -w flag for build backends without
+  prepare_metadata_for_build_wheel hook
+  When used, the wheel is built in %%pyproject_buildrequires
+  and information about runtime requires and extras is read from that wheel.
+
 * Tue Apr 12 2022 Miro Hrončok <mhroncok@redhat.com> - 1.1.0-1
 - %%pyproject_save_files: Support nested directories in dist-info
 

pyproject_buildrequires.py

@@ -1,3 +1,5 @@
+import glob
+import io
 import os
 import sys
 import importlib.metadata
@@ -11,6 +13,7 @@ import re
 import tempfile
 import email.parser
 import pathlib
+import zipfile
 
 from pyproject_requirements_txt import convert_requirements_txt
 
@@ -253,21 +256,67 @@ def generate_build_requirements(backend, requirements):
         requirements.check(source='get_requires_for_build_wheel')
 
 
-def generate_run_requirements(backend, requirements):
+def requires_from_metadata_file(metadata_file):
+    message = email.parser.Parser().parse(metadata_file, headersonly=True)
+    return {k: message.get_all(k, ()) for k in ('Requires', 'Requires-Dist')}
+
+
+def generate_run_requirements_hook(backend, requirements):
     hook_name = 'prepare_metadata_for_build_wheel'
     prepare_metadata = getattr(backend, hook_name, None)
     if not prepare_metadata:
         raise ValueError(
-            'build backend cannot provide build metadata '
+            'The build backend cannot provide build metadata '
-            + '(incl. runtime requirements) before build'
+            '(incl. runtime requirements) before build. '
+            'Use the provisional -w flag to build the wheel and parse the metadata from it, '
+            'or use the -R flag not to generate runtime dependencies.'
         )
     with hook_call():
         dir_basename = prepare_metadata('.')
-    with open(dir_basename + '/METADATA') as f:
+    with open(dir_basename + '/METADATA') as metadata_file:
-        message = email.parser.Parser().parse(f, headersonly=True)
+        for key, requires in requires_from_metadata_file(metadata_file).items():
-    for key in 'Requires', 'Requires-Dist':
+            requirements.extend(requires, source=f'hook generated metadata: {key}')
-        requires = message.get_all(key, ())
+
-        requirements.extend(requires, source=f'wheel metadata: {key}')
+
+def find_built_wheel(wheeldir):
+    wheels = glob.glob(os.path.join(wheeldir, '*.whl'))
+    if not wheels:
+        return None
+    if len(wheels) > 1:
+        raise RuntimeError('Found multiple wheels in %{_pyproject_wheeldir}, '
+                           'this is not supported with %pyproject_buildrequires -w.')
+    return wheels[0]
+
+
+def generate_run_requirements_wheel(backend, requirements, wheeldir):
+    # Reuse the wheel from the previous round of %pyproject_buildrequires (if it exists)
+    wheel = find_built_wheel(wheeldir)
+    if not wheel:
+        import pyproject_wheel
+        returncode = pyproject_wheel.build_wheel(wheeldir=wheeldir, stdout=sys.stderr)
+        if returncode != 0:
+            raise RuntimeError('Failed to build the wheel for %pyproject_buildrequires -w.')
+        wheel = find_built_wheel(wheeldir)
+    if not wheel:
+        raise RuntimeError('Cannot locate the built wheel for %pyproject_buildrequires -w.')
+
+    print_err(f'Reading metadata from {wheel}')
+    with zipfile.ZipFile(wheel) as wheelfile:
+        for name in wheelfile.namelist():
+            if name.count('/') == 1 and name.endswith('.dist-info/METADATA'):
+                with io.TextIOWrapper(wheelfile.open(name), encoding='utf-8') as metadata_file:
+                    for key, requires in requires_from_metadata_file(metadata_file).items():
+                        requirements.extend(requires, source=f'built wheel metadata: {key}')
+                break
+        else:
+            raise RuntimeError('Could not find *.dist-info/METADATA in built wheel.')
+
+
+def generate_run_requirements(backend, requirements, *, build_wheel, wheeldir):
+    if build_wheel:
+        generate_run_requirements_wheel(backend, requirements, wheeldir)
+    else:
+        generate_run_requirements_hook(backend, requirements)
 
 
 def generate_tox_requirements(toxenv, requirements):
@@ -326,7 +375,7 @@ def python3dist(name, op=None, version=None, python3_pkgversion="3"):
 
 
 def generate_requires(
-    *, include_runtime=False, toxenv=None, extras=None,
+    *, include_runtime=False, build_wheel=False, wheeldir=None, toxenv=None, extras=None,
     get_installed_version=importlib.metadata.version,  # for dep injection
     generate_extras=False, python3_pkgversion="3", requirement_files=None, use_build_system=True
 ):
@@ -357,7 +406,7 @@ def generate_requires(
             include_runtime = True
             generate_tox_requirements(toxenv, requirements)
         if include_runtime:
-            generate_run_requirements(backend, requirements)
+            generate_run_requirements(backend, requirements, build_wheel=build_wheel, wheeldir=wheeldir)
     except EndPass:
         return
 
@@ -370,6 +419,15 @@ def main(argv):
         '-r', '--runtime', action='store_true', default=True,
         help='Generate run-time requirements (default, disable with -R)',
     )
+    parser.add_argument(
+        '-w', '--wheel', action='store_true', default=False,
+        help=('Generate run-time requirements by building the wheel '
+              '(useful for build backends without the prepare_metadata_for_build_wheel hook)'),
+    )
+    parser.add_argument(
+        '--wheeldir', metavar='PATH', default=None,
+        help='The directory with wheel, used when -w.',
+    )
     parser.add_argument(
         '-R', '--no-runtime', action='store_false', dest='runtime',
         help="Don't generate run-time requirements (implied by -N)",
@@ -412,6 +470,10 @@ def main(argv):
     if not args.use_build_system:
         args.runtime = False
 
+    if args.wheel:
+        if not args.wheeldir:
+            raise ValueError('--wheeldir must be set when -w.')
+
     if args.toxenv:
         args.tox = True
 
@@ -427,6 +489,8 @@ def main(argv):
     try:
         generate_requires(
             include_runtime=args.runtime,
+            build_wheel=args.wheel,
+            wheeldir=args.wheeldir,
             toxenv=args.toxenv,
             extras=args.extras,
             generate_extras=args.generate_extras,

pyproject_buildrequires_testcases.yaml

@@ -268,6 +268,8 @@ Run dependencies with extras (not selected):
 
         def main():
             setup(
+                name = "pytest",
+                version = "6.6.6",
                 setup_requires=["setuptools>=40.0"],
                 # fmt: off
                 extras_require={
@@ -358,6 +360,35 @@ Run dependencies with multiple extras:
     python3dist(dep1)
   result: 0
 
+Run dependencies with extras and build wheel option:
+  installed:
+    setuptools: 50
+    wheel: 1
+    pyyaml: 1
+  include_runtime: true
+  build_wheel: true
+  extras:
+    - testing
+  setup.py: *pytest_setup_py
+  expected: |
+    python3dist(setuptools) >= 40.8
+    python3dist(wheel)
+    python3dist(wheel)
+    python3dist(setuptools) >= 40
+    python3dist(py) >= 1.5
+    python3dist(six) >= 1.10
+    python3dist(setuptools)
+    python3dist(attrs) >= 17.4
+    python3dist(atomicwrites) >= 1
+    python3dist(pluggy) >= 0.11
+    python3dist(more-itertools) >= 4
+    python3dist(argcomplete)
+    python3dist(hypothesis) >= 3.56
+    python3dist(nose)
+    python3dist(requests)
+  result: 0
+  stderr_contains: "Reading metadata from {wheeldir}/pytest-6.6.6-py3-none-any.whl"
+
 Tox dependencies:
   installed:
     setuptools: 50

pyproject_wheel.py

@@ -0,0 +1,25 @@
+import sys
+import subprocess
+
+
+def build_wheel(*, wheeldir, stdout=None):
+    command = (
+        sys.executable,
+        '-m', 'pip',
+        'wheel',
+        '--wheel-dir', wheeldir,
+        '--no-deps',
+        '--use-pep517',
+        '--no-build-isolation',
+        '--disable-pip-version-check',
+        '--no-clean',
+        '--progress-bar', 'off',
+        '--verbose',
+        '.',
+    )
+    cp = subprocess.run(command, stdout=stdout)
+    return cp.returncode
+
+
+if __name__ == '__main__':
+    sys.exit(build_wheel(wheeldir=sys.argv[1]))

test_pyproject_buildrequires.py

@@ -13,12 +13,14 @@ with Path(__file__).parent.joinpath('pyproject_buildrequires_testcases.yaml').op
 
 
 @pytest.mark.parametrize('case_name', testcases)
-def test_data(case_name, capsys, tmp_path, monkeypatch):
+def test_data(case_name, capfd, tmp_path, monkeypatch):
     case = testcases[case_name]
 
     cwd = tmp_path.joinpath('cwd')
     cwd.mkdir()
     monkeypatch.chdir(cwd)
+    wheeldir = cwd.joinpath('wheeldir')
+    wheeldir.mkdir()
 
     if case.get('xfail'):
         pytest.xfail(case.get('xfail'))
@@ -45,6 +47,8 @@ def test_data(case_name, capsys, tmp_path, monkeypatch):
         generate_requires(
             get_installed_version=get_installed_version,
             include_runtime=case.get('include_runtime', use_build_system),
+            build_wheel=case.get('build_wheel', False),
+            wheeldir=str(wheeldir),
             extras=case.get('extras', []),
             toxenv=case.get('toxenv', None),
             generate_extras=case.get('generate_extras', False),
@@ -64,7 +68,7 @@ def test_data(case_name, capsys, tmp_path, monkeypatch):
         # if we ever need to do that, we can remove the check or change it:
         assert 'expected' in case or 'stderr_contains' in case
 
-        out, err = capsys.readouterr()
+        out, err = capfd.readouterr()
 
         if 'expected' in case:
             assert out == case['expected']
@@ -75,7 +79,7 @@ def test_data(case_name, capsys, tmp_path, monkeypatch):
             if isinstance(stderr_contains, str):
                 stderr_contains = [stderr_contains]
             for expected_substring in stderr_contains:
-                assert expected_substring in err
+                assert expected_substring.format(**locals()) in err
     finally:
         for req in requirement_files:
             req.close()

tests/python-userpath.spec

@@ -8,15 +8,12 @@ Source:         %{pypi_source userpath}
 BuildArch:      noarch
 BuildRequires:  python3-devel
 
-# Manually BuildRequire the runtime dependencies until we have a solution
-# for build backends without prepare_metadata_for_build_wheel():
-BuildRequires:  python3dist(click)
-
 %description
 This package uses hatchling as build backend.
 This package is tested because:
 
- - the prepare_metadata_for_build_wheel hook does not exist
+ - the prepare_metadata_for_build_wheel hook does not exist,
+   %%pyproject_buildrequires -w is used
    https://github.com/ofek/hatch/issues/128
  - the licenses are stored in a dist-info subdirectory
    https://bugzilla.redhat.com/1985340
@@ -39,12 +36,12 @@ sed -Ei '/^(coverage)$/d' requirements-dev.txt
 
 
 %generate_buildrequires
-# Cannot use -r (the default) with hatchling, must use -R
+%pyproject_buildrequires requirements-dev.txt -w
-%pyproject_buildrequires requirements-dev.txt -R
 
 
-%build
+## %%pyproject_buildrequires -w makes this redundant:
-%pyproject_wheel
+#  %%build
+#  %%pyproject_wheel
 
 
 %install