BUG: set _PYTHON_HOST_PLATFOMR env var for the current process too

The environment variable is used to compute the wheel platform tag.
However this happens in process and setting the environment variable
only for forked processes does not affect the tag. This fixes the
wheel filename produced when cross compiling on macOS via the
ARCHFLAGS environment variable.

While at it, simplify a bit the handling of environment variables.

mesonpy/__init__.py

@@ -647,29 +647,28 @@ def __init__(
         self._meson_native_file = self._build_dir / 'meson-python-native-file.ini'
         self._meson_cross_file = self._build_dir / 'meson-python-cross-file.ini'
         self._meson_args: MesonArgs = collections.defaultdict(list)
-        self._env = os.environ.copy()
 
         _check_meson_version()
 
         self._ninja = _env_ninja_command()
         if self._ninja is None:
             raise ConfigError(f'Could not find ninja version {_NINJA_REQUIRED_VERSION} or newer.')
-        self._env.setdefault('NINJA', self._ninja)
+        os.environ.setdefault('NINJA', self._ninja)
 
         # make sure the build dir exists
         self._build_dir.mkdir(exist_ok=True, parents=True)
         self._install_dir.mkdir(exist_ok=True, parents=True)
 
         # setuptools-like ARCHFLAGS environment variable support
         if sysconfig.get_platform().startswith('macosx-'):
-            archflags = self._env.get('ARCHFLAGS', '').strip()
+            archflags = os.environ.get('ARCHFLAGS', '').strip()
             if archflags:
                 arch, *other = filter(None, (x.strip() for x in archflags.split('-arch')))
                 if other:
                     raise ConfigError(f'Multi-architecture builds are not supported but $ARCHFLAGS={archflags!r}')
                 macver, _, nativearch = platform.mac_ver()
                 if arch != nativearch:
-                    x = self._env.setdefault('_PYTHON_HOST_PLATFORM', f'macosx-{macver}-{arch}')
+                    x = os.environ.setdefault('_PYTHON_HOST_PLATFORM', f'macosx-{macver}-{arch}')
                     if not x.endswith(arch):
                         raise ConfigError(f'$ARCHFLAGS={archflags!r} and $_PYTHON_HOST_PLATFORM={x!r} do not agree')
                     family = 'aarch64' if arch == 'arm64' else arch
@@ -736,7 +735,7 @@ def _run(self, cmd: Sequence[str]) -> None:
         # command line appears before the command output. Without it,
         # the lines appear in the wrong order in pip output.
         print('{cyan}{bold}+ {}{reset}'.format(' '.join(cmd), **_STYLES), flush=True)
-        r = subprocess.run(cmd, env=self._env, cwd=self._build_dir)
+        r = subprocess.run(cmd, cwd=self._build_dir)
         if r.returncode != 0:
             raise SystemExit(r.returncode)
 

tests/conftest.py

@@ -156,17 +156,18 @@ def disable_pip_version_check():
 
 @pytest.fixture(scope='session')
 def pep518_wheelhouse(tmp_path_factory):
-    wheelhouse = tmp_path_factory.mktemp('wheelhouse')
-    meson_python = str(package_dir.parent.parent)
+    wheelhouse = os.fspath(tmp_path_factory.mktemp('wheelhouse'))
+    meson_python = os.fspath(package_dir.parent.parent)
     # Populate wheelhouse with wheel for the following packages and
     # their dependencies.  Wheels are downloaded from PyPI or built
     # from the source distribution as needed.  Sources or wheels in
     # the pip cache are used when available.
     packages = [
         meson_python,
     ]
-    subprocess.run([sys.executable, '-m', 'pip', 'wheel', '--wheel-dir', str(wheelhouse), *packages], check=True)
-    return str(wheelhouse)
+    cmd = [sys.executable, '-m', 'pip', 'wheel', '--no-build-isolation', '--wheel-dir', wheelhouse, *packages]
+    subprocess.run(cmd, check=True)
+    return wheelhouse
 
 
 @pytest.fixture

tests/test_wheel.py

@@ -240,3 +240,12 @@ def test_purelib_platlib_split(package_purelib_platlib_split, tmp_path):
     with pytest.raises(mesonpy.BuildError, match='The purelib-platlib-split package is split'):
         with mesonpy.Project.with_temp_working_dir() as project:
             project.wheel(tmp_path)
+
+
+@pytest.mark.skipif(platform.system() != 'Darwin', reason='macOS specific test')
+@pytest.mark.parametrize(('arch'), ['x86_64', 'arm64'])
+def test_archflags_envvar(package_purelib_and_platlib, monkeypatch, tmp_path, arch):
+    monkeypatch.setenv('ARCHFLAGS', f'-arch {arch}')
+    filename = mesonpy.build_wheel(tmp_path)
+    name = wheel.wheelfile.WheelFile(tmp_path / filename).parsed_filename
+    assert name.group('plat').endswith(arch)