BUG: correctly handle empty directories when checking package splits

mesonpy/__init__.py

@@ -146,7 +146,6 @@ def _map_to_wheel(sources: Dict[str, Dict[str, Any]],
                   exclude: List[str], include: List[str]) -> DefaultDict[str, List[_Entry]]:
     """Map files to the wheel, organized by wheel installation directory."""
     wheel_files: DefaultDict[str, List[_Entry]] = collections.defaultdict(list)
-    packages: Dict[str, str] = {}
     excluded = _compile_patterns(exclude)
     included = _compile_patterns(include)
 
@@ -165,18 +164,6 @@ def _map_to_wheel(sources: Dict[str, Dict[str, Any]],
             if path is None:
                 raise BuildError(f'Could not map installation path to an equivalent wheel directory: {str(destination)!r}')
 
-            if path == 'purelib' or path == 'platlib':
-                package = destination.parts[1]
-                other = packages.setdefault(package, path)
-                if other != path:
-                    this = os.fspath(pathlib.Path(path, *destination.parts[1:]))
-                    module = next(entry.dst for entry in wheel_files[other] if entry.dst.parts[0] == destination.parts[1])
-                    that = os.fspath(other / module)
-                    raise BuildError(
-                        f'The {package} package is split between {path} and {other}: '
-                        f'{this!r} and {that!r}, a "pure: false" argument may be missing in meson.build. '
-                        f'It is recommended to set it in "import(\'python\').find_installation()"')
-
             if key == 'install_subdirs' or key == 'targets' and os.path.isdir(src):
                 exclude_files = {os.path.normpath(x) for x in target.get('exclude_files', [])}
                 exclude_dirs = {os.path.normpath(x) for x in target.get('exclude_dirs', [])}
@@ -208,6 +195,21 @@ def _map_to_wheel(sources: Dict[str, Dict[str, Any]],
 
                 wheel_files[path].append(_Entry(dst, src, install_rpath, build_rpath))
 
+    # Verify that packages are not split between ``platlib`` and ``purelib``.
+    if wheel_files.get('purelib') and wheel_files.get('platlib'):
+        packages: dict[str, tuple[str, pathlib.Path]] = {}
+        for path in 'purelib', 'platlib':
+            for entry in wheel_files[path]:
+                package = entry.dst.parts[0]
+                other, module = packages.setdefault(package, (path, entry.dst))
+                if other != path:
+                    this = os.fspath(path / entry.dst)
+                    that = os.fspath(other / module)
+                    raise BuildError(
+                        f'The {package} package is split between {path} and {other}: '
+                        f'{this!r} and {that!r}, a "pure: false" argument may be missing in meson.build. '
+                        f'It is recommended to set it in "import(\'python\').find_installation()"')
+
     return wheel_files
 
 

tests/packages/install-subdir/meson.build

@@ -7,21 +7,43 @@ project('install-subdir', version: '1.0.0')
 py = import('python').find_installation()
 
 install_subdir(
-  'subdir',
-  exclude_files: 'excluded.py',
-  exclude_directories: 'excluded',
-  install_dir: py.get_install_dir(pure: false),
+    'subdir',
+    exclude_files: 'excluded.py',
+    exclude_directories: 'excluded',
+    install_dir: py.get_install_dir(pure: false),
 )
 
 install_subdir(
-  'strip',
-  strip_directory: true,
-  exclude_files: 'excluded.py',
-  install_dir: py.get_install_dir(pure: false) / 'test',
+    'strip',
+    strip_directory: true,
+    exclude_files: 'excluded.py',
+    install_dir: py.get_install_dir(pure: false) / 'test',
 )
 
 install_subdir(
-  'nested',
-  exclude_files: 'deep/excluded.py',
-  install_dir: py.get_install_dir(pure: false),
+    'nested',
+    exclude_files: 'deep/excluded.py',
+    install_dir: py.get_install_dir(pure: false),
+)
+
+# The two install_subdir() below are used to verify package split checks in
+# presence of install_subdir() that do not result in any file added to the
+# wheel.
+
+# Due to the exclude_files argument, this install_subdir() does not result
+# into any file installed, however, this is supported only with Meson 1.1.0
+# and later.  For simplicity, leave it out on older Meson versions.
+if meson.version().version_compare('>= 1.1')
+    install_subdir(
+        'purelib',
+        strip_directory: true,
+        exclude_files: 'excluded.py',
+        install_dir: py.get_install_dir(pure: true) / 'example',
+    )
+endif
+
+install_subdir(
+    'platlib',
+    strip_directory: true,
+    install_dir: py.get_install_dir(pure: false) / 'example',
 )

tests/packages/install-subdir/platlib/lib.py

@@ -0,0 +1,3 @@
+# SPDX-FileCopyrightText: 2026 The meson-python developers
+#
+# SPDX-License-Identifier: MIT

tests/packages/install-subdir/purelib/excluded.py

@@ -0,0 +1,3 @@
+# SPDX-FileCopyrightText: 2026 The meson-python developers
+#
+# SPDX-License-Identifier: MIT

tests/test_wheel.py

@@ -441,11 +441,12 @@ def test_install_subdir(wheel_install_subdir):
     # Meson 1.1.0, see https://github.com/mesonbuild/meson/pull/11432.
     # Run the test anyway to ensure that meson-python can produce a
     # wheel also for older versions of Meson.
-    if MESON_VERSION >= (1, 1, 99):
+    if MESON_VERSION >= (1, 1, 0):
         assert set(artifact.namelist()) == {
             'install_subdir-1.0.0.dist-info/METADATA',
             'install_subdir-1.0.0.dist-info/RECORD',
             'install_subdir-1.0.0.dist-info/WHEEL',
+            'example/lib.py',
             'subdir/__init__.py',
             'subdir/test.py',
             'test/module.py',