Handle directory-open errors through on_error during tree walks

CHANGES.rst

@@ -20,6 +20,8 @@ New features:
 
 Bug fixes:
 
+- Honor `on_error` when opening a directory fails during tree traversal.
+
 - `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

@@ -17,6 +17,8 @@ New features:
 
 Bug fixes:
 
+- Honor `on_error` when opening a directory fails during tree traversal.
+
 - `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

@@ -322,7 +322,15 @@ def _iter_tree_entries_next(
 	else:
 		raise RecursionError(real_path=dir_real, first_path=memo[dir_real], second_path=dir_rel)
 
-	with os.scandir(dir_full) as scan_iter:
+	try:
+		scan_iter = os.scandir(dir_full)
+	except OSError as e:
+		del memo[dir_real]
+		if on_error is not None:
+			on_error(e)
+		return
+
+	with scan_iter:
 		node_ent: os.DirEntry
 		for node_ent in scan_iter:
 			node_rel = os.path.join(dir_rel, node_ent.name)
@@ -450,7 +458,15 @@ def _iter_tree_files_next(
 	else:
 		raise RecursionError(real_path=dir_real, first_path=memo[dir_real], second_path=dir_rel)
 
-	with os.scandir(dir_full) as scan_iter:
+	try:
+		scan_iter = os.scandir(dir_full)
+	except OSError as e:
+		del memo[dir_real]
+		if on_error is not None:
+			on_error(e)
+		return
+
+	with scan_iter:
 		node_ent: os.DirEntry
 		for node_ent in scan_iter:
 			node_rel = os.path.join(dir_rel, node_ent.name)

tests/test_01_util.py

@@ -18,6 +18,8 @@
 from typing import (
 	ClassVar,
 	Optional)  # Replaced by `X | None` in 3.10.
+from unittest.mock import (
+	patch)
 
 from pathspec.patterns.gitignore.basic import (
 	GitIgnoreBasicPattern)
@@ -161,6 +163,51 @@ def tearDown(self) -> None:
 		"""
 		shutil.rmtree(self.temp_dir)
 
+	def test_scan_missing_directory(self):
+		"""Directory scan failures honor the error handler."""
+		missing = os.path.join(self.temp_dir, 'missing')
+		for walk in (iter_tree_entries, iter_tree_files):
+			for mode in ('ignore', 'record', 'raise'):
+				with self.subTest(walk=walk.__name__, mode=mode):
+					errors = []
+
+					def on_error(error):
+						errors.append(error)
+						if mode == 'raise':
+							raise RuntimeError('stop walking') from error
+
+					handler = None if mode == 'ignore' else on_error
+					if mode == 'raise':
+						with self.assertRaisesRegex(RuntimeError, 'stop walking'):
+							list(walk(missing, on_error=handler))
+					else:
+						self.assertEqual(list(walk(missing, on_error=handler)), [])
+					if mode != 'ignore':
+						self.assertEqual(len(errors), 1)
+						self.assertEqual(errors[0].errno, errno.ENOENT)
+
+	def test_scan_inaccessible_child(self):
+		"""An inaccessible child does not prevent walking readable siblings."""
+		self.make_dirs(['blocked'])
+		self.make_files(['kept.txt'])
+		scandir = os.scandir
+		error = PermissionError(errno.EACCES, 'permission denied', 'blocked')
+
+		def scan(path):
+			if os.path.basename(path) == 'blocked':
+				raise error
+			return scandir(path)
+
+		for walk in (iter_tree_entries, iter_tree_files):
+			for record in (False, True):
+				with self.subTest(walk=walk.__name__, record=record):
+					errors = []
+					with patch('pathspec.util.os.scandir', side_effect=scan):
+						results = list(walk(self.temp_dir, on_error=errors.append if record else None))
+					paths = get_paths_from_entries(results) if walk is iter_tree_entries else set(results)
+					self.assertIn('kept.txt', paths)
+					self.assertEqual(errors, [error] if record else [])
+
 	def test_01_files_1_entries(self):
 		"""
 		Tests to make sure all files are found.