Allow subtree traversal from filesystem roots

CHANGES.rst

@@ -19,6 +19,7 @@ New features:
 
 Bug fixes:
 
+- Fixed subtree traversal from filesystem roots and equivalent Windows paths with different casing.
 - `Pull #123`_: Ignore invalid gitignore bracket ranges for `GitIgnoreSpec`.
 - `Pull #128`_: Support POSIX character classes (e.g. `[[:alpha:]]`) in gitignore bracket expressions.
 - `Issue #129`_ / `Pull #132`_: Fix GitIgnoreSpec re-including files under an excluded directory

CHANGES_1.in.rst

@@ -16,6 +16,7 @@ New features:
 
 Bug fixes:
 
+- Fixed subtree traversal from filesystem roots and equivalent Windows paths with different casing.
 - `Pull #123`_: Ignore invalid gitignore bracket ranges for `GitIgnoreSpec`.
 - `Pull #128`_: Support POSIX character classes (e.g. `[[:alpha:]]`) in gitignore bracket expressions.
 - `Issue #129`_ / `Pull #132`_: Fix GitIgnoreSpec re-including files under an excluded directory

pathspec/util.py

@@ -209,9 +209,9 @@ def _get_sub_path_safe(root: str, sub_dir: StrPath) -> str:
 	Returns the sub-directory path relative to the root directory (:class:`str`).
 	"""
 	sub_abs = os.path.normpath(os.path.join(root, sub_dir))
-	if sub_abs == root:
+	if os.path.normcase(sub_abs) == os.path.normcase(root):
 		return ''
-	elif sub_abs.startswith(root + os.sep):
+	elif os.path.commonpath((root, sub_abs)) == root:
 		return os.path.relpath(sub_abs, root)
 	else:
 		raise ValueError(f"{sub_dir=!r} must be relative to {root=!r}.")

tests/test_01_util.py

@@ -218,6 +218,39 @@ def test_01_files_2_files(self):
 			'Dir/Inner/f',
 		])))
 
+	def test_subdir_from_filesystem_root(self):
+		"""Traverse only the requested subtree when the root ends in a separator."""
+		self.make_files(['a.txt'])
+		root = Path(self.temp_dir).anchor
+		expected = {os.path.relpath(os.path.join(self.temp_dir, 'a.txt'), root)}
+		for subdir in (self.temp_dir, os.path.relpath(self.temp_dir, root)):
+			with self.subTest(subdir=subdir):
+				self.assertEqual(set(iter_tree_files(root, subdir=subdir)), expected)
+				self.assertEqual(
+					get_paths_from_entries(iter_tree_entries(root, subdir=subdir)), expected)
+
+	def test_subdir_same_root(self):
+		"""Both an absolute root and a dot select the root itself."""
+		self.make_files(['a.txt'])
+		for subdir in ('.', self.temp_dir):
+			with self.subTest(subdir=subdir):
+				self.assertEqual(set(iter_tree_files(self.temp_dir, subdir=subdir)), {'a.txt'})
+
+	def test_subdir_rejects_outside_root(self):
+		"""Reject parents and sibling paths sharing the root's string prefix."""
+		for subdir in ('..', os.path.join('..', 'other'), str(self.temp_dir) + '-other'):
+			for traverse in (iter_tree_files, iter_tree_entries):
+				with self.subTest(subdir=subdir, traverse=traverse):
+					with self.assertRaises(ValueError):
+						list(traverse(self.temp_dir, subdir=subdir))
+
+	@unittest.skipUnless(os.path.normcase('A') == os.path.normcase('a'), 'Case-sensitive paths')
+	def test_subdir_case_insensitive_root(self):
+		"""Accept equivalent root paths with different casing on Windows."""
+		self.make_files(['a.txt'])
+		root = str(self.temp_dir).swapcase()
+		self.assertEqual(set(iter_tree_files(root, subdir=self.temp_dir)), {'a.txt'})
+
 	def test_02_link_1_check_symlink(self):
 		"""
 		Tests whether links can be created.