Expand to long paths when resolving collection arguments

Author: nicoddemus

src/_pytest/compat.py

@@ -1,5 +1,5 @@
 # mypy: allow-untyped-defs
-"""Python version compatibility code."""
+"""Python version and platform compatibility code."""
 from __future__ import annotations
 
 import dataclasses
@@ -301,6 +301,38 @@ def get_user_id() -> int | None:
         return uid if uid != ERROR else None
 
 
+if sys.platform == "win32":
+    from ctypes import create_unicode_buffer
+    from ctypes import windll
+
+    def ensure_long_path(p: Path) -> Path:
+        """
+        Ensures the given path contains its long form in Windows.
+
+        Short-paths follow the DOS restriction of 8 characters + 3 chars for file extension,
+        and are still supported by Windows.
+        """
+        if not p.exists():
+            return p
+        short_path = os.fspath(p)
+        # Use a buffer twice the size of the original path size to (reasonably) ensure we will be able
+        # to hold the long path.
+        buffer_size = len(short_path) * 2
+        buffer = create_unicode_buffer(buffer_size)
+        windll.kernel32.GetLongPathNameW(short_path, buffer, buffer_size)
+        long_path_str = buffer.value
+        # If we could not convert it, probably better to hard-crash this now rather
+        # than later.
+        assert long_path_str, f"Failed to convert short path to long path form:\n(size: {len(short_path)}):{short_path}"
+        return Path(buffer.value)
+
+else:
+
+    def ensure_long_path(p: Path) -> Path:
+        """No-op in other platforms."""
+        return p
+
+
 # Perform exhaustiveness checking.
 #
 # Consider this example:

src/_pytest/main.py

@@ -28,6 +28,7 @@
 
 from _pytest import nodes
 import _pytest._code
+from _pytest.compat import ensure_long_path
 from _pytest.config import Config
 from _pytest.config import directory_arg
 from _pytest.config import ExitCode
@@ -901,10 +902,6 @@ def collect(self) -> Iterator[Union[nodes.Item, nodes.Collector]]:
                     # Path part e.g. `/a/b/` in `/a/b/test_file.py::TestIt::test_it`.
                     if isinstance(matchparts[0], Path):
                         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).
-                            is_match = os.path.samefile(node.path, matchparts[0])
                     # Name part e.g. `TestIt` in `/a/b/test_file.py::TestIt::test_it`.
                     else:
                         # TODO: Remove parametrized workaround once collection structure contains
@@ -1012,4 +1009,6 @@ def resolve_collection_argument(
             else "directory argument cannot contain :: selection parts: {arg}"
         )
         raise UsageError(msg.format(arg=arg))
+    # Ensure we expand short paths to long paths on Windows (#11895).
+    fspath = ensure_long_path(fspath)
     return fspath, parts

testing/test_collection.py

@@ -9,6 +9,7 @@
 from typing import List
 
 from _pytest.assertion.util import running_on_ci
+from _pytest.compat import ensure_long_path
 from _pytest.config import ExitCode
 from _pytest.fixtures import FixtureRequest
 from _pytest.main import _in_venv
@@ -1746,27 +1747,43 @@ def test_foo(): assert True
     assert result.parseoutcomes() == {"passed": 1}
 
 
-@pytest.mark.skipif(not sys.platform.startswith("win"), reason="Windows only")
-def test_collect_short_file_windows(pytester: Pytester) -> None:
-    """Reproducer for #11895: short paths not colleced on Windows."""
-    short_path = tempfile.mkdtemp()
-    if "~" not in short_path:  # pragma: no cover
-        if running_on_ci():
-            # On CI, we are expecting that under the current GitHub actions configuration,
-            # tempfile.mkdtemp() is producing short paths, so we want to fail to prevent
-            # this from silently changing without us noticing.
-            pytest.fail(
-                f"tempfile.mkdtemp() failed to produce a short path on CI: {short_path}"
-            )
-        else:
-            # We want to skip failing this test locally in this situation because
-            # depending on the local configuration tempfile.mkdtemp() might not produce a short path:
-            # For example, user might have configured %TEMP% exactly to avoid generating short paths.
-            pytest.skip(
-                f"tempfile.mkdtemp() failed to produce a short path: {short_path}, skipping"
-            )
-
-    test_file = Path(short_path).joinpath("test_collect_short_file_windows.py")
-    test_file.write_text("def test(): pass", encoding="UTF-8")
-    result = pytester.runpytest(short_path)
-    assert result.parseoutcomes() == {"passed": 1}
+class TestCollectionShortPaths:
+    @pytest.fixture
+    def short_path(self) -> Path:
+        short_path = tempfile.mkdtemp()
+        if "~" not in short_path:  # pragma: no cover
+            if running_on_ci():
+                # On CI, we are expecting that under the current GitHub actions configuration,
+                # tempfile.mkdtemp() is producing short paths, so we want to fail to prevent
+                # this from silently changing without us noticing.
+                pytest.fail(
+                    f"tempfile.mkdtemp() failed to produce a short path on CI: {short_path}"
+                )
+            else:
+                # We want to skip failing this test locally in this situation because
+                # depending on the local configuration tempfile.mkdtemp() might not produce a short path:
+                # For example, user might have configured %TEMP% exactly to avoid generating short paths.
+                pytest.skip(
+                    f"tempfile.mkdtemp() failed to produce a short path: {short_path}, skipping"
+                )
+        return Path(short_path)
+
+    @pytest.mark.skipif(not sys.platform.startswith("win"), reason="Windows only")
+    def test_ensure_long_path_win(self, short_path: Path) -> None:
+        long_path = ensure_long_path(short_path)
+        assert len(os.fspath(long_path)) > len(os.fspath(short_path))
+
+    @pytest.mark.skipif(not sys.platform.startswith("win"), reason="Windows only")
+    def test_collect_short_file_windows(
+        self, pytester: Pytester, short_path: Path
+    ) -> None:
+        """Reproducer for #11895: short paths not collected on Windows."""
+        test_file = short_path.joinpath("test_collect_short_file_windows.py")
+        test_file.write_text("def test(): pass", encoding="UTF-8")
+        result = pytester.runpytest(short_path)
+        assert result.parseoutcomes() == {"passed": 1}
+
+    def test_ensure_long_path_general(self, tmp_path: Path) -> None:
+        """Sanity check: a normal path to ensure_long_path works on all platforms."""
+        assert ensure_long_path(tmp_path) == tmp_path
+        assert ensure_long_path(tmp_path / "non-existent") == tmp_path / "non-existent"