main: use a better windows short-path comparison method

The previous check does not account for multiple levels of symlinks:
given a -> b -> c, a would match b.

Author: bluetech

changelog/13598.bugfix.rst

@@ -0,0 +1 @@
+Fixed possible collection confusion on Windows when short paths and symlinks are involved.

src/_pytest/main.py

@@ -39,6 +39,7 @@
 from _pytest.pathlib import bestrelpath
 from _pytest.pathlib import fnmatch_ex
 from _pytest.pathlib import safe_exists
+from _pytest.pathlib import samefile_nofollow
 from _pytest.pathlib import scandir
 from _pytest.reports import CollectReport
 from _pytest.reports import TestReport
@@ -935,14 +936,10 @@ def collect(self) -> Iterator[nodes.Item | nodes.Collector]:
                         is_match = node.path == matchparts[0]
                         if sys.platform == "win32" and not is_match:
                             # In case the file paths do not match, fallback to samefile() to
-                            # account for short-paths on Windows (#11895).
-                            same_file = os.path.samefile(node.path, matchparts[0])
-                            # We don't want to match links to the current node,
-                            # otherwise we would match the same file more than once (#12039).
-                            is_match = same_file and (
-                                os.path.islink(node.path)
-                                == os.path.islink(matchparts[0])
-                            )
+                            # account for short-paths on Windows (#11895). But use a version
+                            # which doesn't resolve symlinks, otherwise we might match the
+                            # same file more than once (#12039).
+                            is_match = samefile_nofollow(node.path, matchparts[0])
 
                     # Name part e.g. `TestIt` in `/a/b/test_file.py::TestIt::test_it`.
                     else:

src/_pytest/pathlib.py

@@ -1053,3 +1053,11 @@ def safe_exists(p: Path) -> bool:
         # ValueError: stat: path too long for Windows
         # OSError: [WinError 123] The filename, directory name, or volume label syntax is incorrect
         return False
+
+
+def samefile_nofollow(p1: Path, p2: Path) -> bool:
+    """Test whether two paths reference the same actual file or directory.
+
+    Unlike Path.samefile(), does not resolve symlinks.
+    """
+    return os.path.samestat(p1.lstat(), p2.lstat())

testing/test_collection.py

@@ -1780,6 +1780,41 @@ def test_collect_short_file_windows(pytester: Pytester) -> None:
     assert result.parseoutcomes() == {"passed": 1}
 
 
+def test_collect_short_file_windows_multi_level_symlink(
+    pytester: Pytester,
+    request: FixtureRequest,
+) -> None:
+    """Regression test for multi-level Windows short-path comparison with
+    symlinks.
+
+    Previously, when matching collection arguments against collected nodes on
+    Windows, the short path fallback resolved symlinks. With a chain a -> b ->
+    target, comparing 'a' against 'b' would incorrectly succeed because both
+    resolved to 'target', which could cause incorrect matching or duplicate
+    collection.
+    """
+    # Prepare target directory with a test file.
+    short_path = Path(tempfile.mkdtemp())
+    request.addfinalizer(lambda: shutil.rmtree(short_path, ignore_errors=True))
+    target = short_path / "target"
+    target.mkdir()
+    (target / "test_chain.py").write_text("def test_chain(): pass", encoding="UTF-8")
+
+    # Create multi-level symlink chain: a -> b -> target.
+    b = short_path / "b"
+    a = short_path / "a"
+    symlink_or_skip(target, b, target_is_directory=True)
+    symlink_or_skip(b, a, target_is_directory=True)
+
+    # Collect via the first symlink; should find exactly one test.
+    result = pytester.runpytest(a)
+    result.assert_outcomes(passed=1)
+
+    # Collect via the intermediate symlink; also exactly one test.
+    result = pytester.runpytest(b)
+    result.assert_outcomes(passed=1)
+
+
 def test_pyargs_collection_tree(pytester: Pytester, monkeypatch: MonkeyPatch) -> None:
     """When using `--pyargs`, the collection tree of a pyargs collection
     argument should only include parents in the import path, not up to confcutdir.