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

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/2026-05-08-11-59-00.gh-issue-149137.Bp3xQz.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.