gh-149137: Fix PackagePath to normalize backslashes from Windows RECORD files

Per the packaging spec, backslashes are valid path separators on Windows
in RECORD files. However, PackagePath extends PurePosixPath which treats
backslashes as literal characters rather than separators, causing .name
and .parts to return incorrect values (e.g., the full path string instead
of just the filename).

Fix by overriding __init__ in PackagePath to replace backslashes with
forward slashes before passing to PurePosixPath.

Author: starkk242

Lib/importlib/metadata/__init__.py

@@ -377,6 +377,16 @@ class PackagePath(pathlib.PurePosixPath):
     size: int
     dist: Distribution
 
+    def __init__(self, *args):
+        # Normalize Windows backslashes to forward slashes. Per the packaging
+        # spec, backslashes are valid path separators in RECORD files on Windows,
+        # but PurePosixPath treats them as literal characters, not separators.
+        normalized = tuple(
+            arg.replace('\\', '/') if isinstance(arg, str) else arg
+            for arg in args
+        )
+        super().__init__(*normalized)
+
     def read_text(self, encoding: str = 'utf-8') -> str:
         return self.locate().read_text(encoding=encoding)
 

Lib/test/test_importlib/metadata/test_main.py

@@ -14,6 +14,7 @@
     EntryPoint,
     MetadataNotFound,
     PackageNotFoundError,
+    PackagePath,
     _unique,
     distributions,
     entry_points,
@@ -491,3 +492,21 @@ def test_origin(self):
         dist = Distribution.from_name('distinfo-pkg')
         assert dist.origin.url.endswith('.whl')
         assert dist.origin.archive_info.hashes.sha256
+
+
+class PackagePathTests(unittest.TestCase):
+    def test_backslash_in_name(self):
+        # Windows RECORD files may use backslashes as path separators per
+        # the packaging spec; PackagePath must normalize them so that
+        # .name/.parts/.parent behave correctly.
+        p = PackagePath('dist_info-1.0.dist-info\\METADATA')
+        self.assertEqual(p.name, 'METADATA')
+
+    def test_backslash_parts(self):
+        p = PackagePath('a\\b\\c.py')
+        self.assertEqual(p.parts, ('a', 'b', 'c.py'))
+
+    def test_forward_slash_unchanged(self):
+        p = PackagePath('dist_info-1.0.dist-info/METADATA')
+        self.assertEqual(p.name, 'METADATA')
+        self.assertEqual(p.parts, ('dist_info-1.0.dist-info', 'METADATA'))

Misc/NEWS.d/next/Library/2026-05-08-fix-packagepath-backslash.gh-issue-149137.rst

@@ -0,0 +1,6 @@
+Fix :class:`importlib.metadata.PackagePath` to normalize Windows backslash
+path separators from RECORD files to forward slashes. Per the packaging
+specification, backslashes are valid separators on Windows, but
+:class:`~pathlib.PurePosixPath` treats them as literal characters, causing
+:attr:`~pathlib.PurePath.name` and :attr:`~pathlib.PurePath.parts` to return
+incorrect values.