Fix removal of very long paths on Windows

AUTHORS

@@ -277,6 +277,7 @@ Tom Dalton
 Tom Viner
 Tomáš Gavenčiak
 Tomer Keren
+Tor Colvin
 Trevor Bekolay
 Tyler Goodlet
 Tzu-ping Chung

changelog/6755.bugfix.rst

@@ -0,0 +1 @@
+Support deleting paths longer than 260 characters on windows created inside tmpdir.

src/_pytest/pathlib.py

@@ -100,10 +100,41 @@ def chmod_rw(p: str) -> None:
     return True
 
 
+def ensure_extended_length_path(path: Path) -> Path:
+    """Get the extended-length version of a path (Windows).
+
+    On Windows, by default, the maximum length of a path (MAX_PATH) is 260
+    characters, and operations on paths longer than that fail. But it is possible
+    to overcome this by converting the path to "extended-length" form before
+    performing the operation:
+    https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation
+
+    On Windows, this function returns the extended-length absolute version of path.
+    On other platforms it returns path unchanged.
+    """
+    if sys.platform.startswith("win32"):
+        path = path.resolve()
+        path = Path(get_extended_length_path_str(str(path)))
+    return path
+
+
+def get_extended_length_path_str(path: str) -> str:
+    """Converts to extended length path as a str"""
+    long_path_prefix = "\\\\?\\"
+    unc_long_path_prefix = "\\\\?\\UNC\\"
+    if path.startswith((long_path_prefix, unc_long_path_prefix)):
+        return path
+    # UNC
+    if path.startswith("\\\\"):
+        return unc_long_path_prefix + path[2:]
+    return long_path_prefix + path
+
+
 def rm_rf(path: Path) -> None:
     """Remove the path contents recursively, even if some elements
     are read-only.
     """
+    path = ensure_extended_length_path(path)
     onerror = partial(on_rm_rf_error, start_path=path)
     shutil.rmtree(str(path), onerror=onerror)
 
@@ -220,6 +251,7 @@ def cleanup_on_exit(lock_path: Path = lock_path, original_pid: int = pid) -> Non
 
 def maybe_delete_a_numbered_dir(path: Path) -> None:
     """removes a numbered directory if its lock can be obtained and it does not seem to be in use"""
+    path = ensure_extended_length_path(path)
     lock_path = None
     try:
         lock_path = create_cleanup_lock(path)

testing/test_pathlib.py

@@ -5,6 +5,7 @@
 
 import pytest
 from _pytest.pathlib import fnmatch_ex
+from _pytest.pathlib import get_extended_length_path_str
 from _pytest.pathlib import get_lock_path
 from _pytest.pathlib import maybe_delete_a_numbered_dir
 from _pytest.pathlib import Path
@@ -89,3 +90,26 @@ def renamed_failed(*args):
     lock_path = get_lock_path(path)
     maybe_delete_a_numbered_dir(path)
     assert not lock_path.is_file()
+
+
+def test_long_path_during_cleanup(tmp_path):
+    """Ensure that deleting long path works (particularly on Windows (#6775))."""
+    path = (tmp_path / ("a" * 250)).resolve()
+    if sys.platform == "win32":
+        # make sure that the full path is > 260 characters without any
+        # component being over 260 characters
+        assert len(str(path)) > 260
+        extended_path = "\\\\?\\" + str(path)
+    else:
+        extended_path = str(path)
+    os.mkdir(extended_path)
+    assert os.path.isdir(extended_path)
+    maybe_delete_a_numbered_dir(path)
+    assert not os.path.isdir(extended_path)
+
+
+def test_get_extended_length_path_str():
+    assert get_extended_length_path_str(r"c:\foo") == r"\\?\c:\foo"
+    assert get_extended_length_path_str(r"\\share\foo") == r"\\?\UNC\share\foo"
+    assert get_extended_length_path_str(r"\\?\UNC\share\foo") == r"\\?\UNC\share\foo"
+    assert get_extended_length_path_str(r"\\?\c:\foo") == r"\\?\c:\foo"