Fix gitignore trailing-space trim for escaped spaces

pathspec/patterns/gitignore/base.py

@@ -296,6 +296,30 @@ def _translate_segment_glob(
 		return regex
 
 
+
+def trim_trailing_spaces(pattern: str) -> str:
+	"""
+	Remove trailing spaces that are not escaped with a backslash.
+
+	This matches Git's *trim_trailing_spaces()* in *dir.c*: a trailing space is
+	kept only when preceded by an odd number of consecutive backslashes. Extra
+	unescaped spaces after an escaped space are still stripped, and an even
+	backslash run does not escape the following space.
+	"""
+	while pattern.endswith(' '):
+		# Count consecutive backslashes immediately before this trailing space.
+		i = len(pattern) - 2
+		run = 0
+		while i >= 0 and pattern[i] == '\\':
+			run += 1
+			i -= 1
+		if run % 2 == 1:
+			# Odd run → the space is escaped; stop trimming.
+			break
+		pattern = pattern[:-1]
+	return pattern
+
+
 class GitIgnorePatternError(ValueError):
 	"""
 	The :class:`GitIgnorePatternError` class indicates an invalid gitignore

pathspec/patterns/gitignore/basic.py

@@ -18,7 +18,8 @@
 from .base import (
 	GitIgnorePatternError,
 	_BYTES_ENCODING,
-	_GitIgnoreBasePattern)
+	_GitIgnoreBasePattern,
+	trim_trailing_spaces)
 
 
 class GitIgnoreBasicPattern(_GitIgnoreBasePattern):
@@ -156,14 +157,10 @@ def pattern_to_regex(
 		original_pattern = pattern_str
 		del pattern
 
-		if pattern_str.endswith('\\ '):
-			# EDGE CASE: Spaces can be escaped with backslash. If a pattern that ends
-			# with a backslash is followed by a space, do not strip from the left.
-			pass
-		else:
-			# EDGE CASE: Leading spaces should be kept (only trailing spaces should be
-			# removed).
-			pattern_str = pattern_str.rstrip()
+		# EDGE CASE: Trailing spaces are stripped unless escaped with a backslash.
+		# A space is escaped only when preceded by an odd number of consecutive
+		# backslashes (Git dir.c trim_trailing_spaces). Leading spaces are kept.
+		pattern_str = trim_trailing_spaces(pattern_str)
 
 		regex: Optional[str]
 		include: Optional[bool]

pathspec/patterns/gitignore/spec.py

@@ -21,7 +21,8 @@
 	GitIgnorePatternError,
 	_BYTES_ENCODING,
 	_GitIgnoreBasePattern,
-	_RangeError)
+	_RangeError,
+	trim_trailing_spaces)
 
 _DIR_MARK = 'ps_d'
 """
@@ -190,14 +191,10 @@ def pattern_to_regex(
 		original_pattern = pattern_str
 		del pattern
 
-		if pattern_str.endswith('\\ '):
-			# EDGE CASE: Spaces can be escaped with backslash. If a pattern that ends
-			# with a backslash is followed by a space, do not strip from the left.
-			pass
-		else:
-			# EDGE CASE: Leading spaces should be kept (only trailing spaces should be
-			# removed). Git does not remove leading spaces.
-			pattern_str = pattern_str.rstrip()
+		# EDGE CASE: Trailing spaces are stripped unless escaped with a backslash.
+		# A space is escaped only when preceded by an odd number of consecutive
+		# backslashes (Git dir.c trim_trailing_spaces). Leading spaces are kept.
+		pattern_str = trim_trailing_spaces(pattern_str)
 
 		regex: Optional[str]
 		include: Optional[bool]

tests/test_07_gitignore_escaped_trailing_spaces.py

@@ -0,0 +1,47 @@
+"""Regression: gitignore trailing-space trimming must match Git dir.c."""
+
+import unittest
+
+from pathspec import PathSpec
+from pathspec.patterns.gitignore.base import trim_trailing_spaces
+from pathspec.patterns.gitignore.basic import GitIgnoreBasicPattern
+from pathspec.patterns.gitignore.spec import GitIgnoreSpecPattern
+
+
+class TrimTrailingSpacesTest(unittest.TestCase):
+	def test_extra_spaces_after_escaped_space(self):
+		# Git: 'bar\\  ' (backslash, space, space) → keep escaped space only.
+		self.assertEqual(trim_trailing_spaces('bar\\  '), 'bar\\ ')
+		self.assertEqual(trim_trailing_spaces('bar\\   '), 'bar\\ ')
+
+	def test_even_backslash_run_strips_space(self):
+		# Even backslashes: space is unescaped and must be stripped.
+		self.assertEqual(trim_trailing_spaces('foo\\\\ '), 'foo\\\\')
+		self.assertEqual(trim_trailing_spaces('foo\\\\\\\\ '), 'foo\\\\\\\\')
+
+	def test_odd_backslash_run_keeps_space(self):
+		self.assertEqual(trim_trailing_spaces('foo\\ '), 'foo\\ ')
+		self.assertEqual(trim_trailing_spaces('foo\\\\\\ '), 'foo\\\\\\ ')
+
+	def test_plain_trailing_spaces(self):
+		self.assertEqual(trim_trailing_spaces('foo  '), 'foo')
+		self.assertEqual(trim_trailing_spaces('foo'), 'foo')
+
+
+class PathSpecEscapedTrailingSpaceTest(unittest.TestCase):
+	def test_pathspec_matches_file_with_trailing_space(self):
+		# Previously raised GitIgnorePatternError (dangling backslash).
+		spec = PathSpec.from_lines('gitwildmatch', ['bar\\  '])
+		self.assertFalse(spec.match_file('bar'))
+		self.assertTrue(spec.match_file('bar '))
+		self.assertFalse(spec.match_file('bar  '))
+
+	def test_basic_and_spec_pattern_classes(self):
+		for cls in (GitIgnoreBasicPattern, GitIgnoreSpecPattern):
+			pattern = cls('bar\\  ')
+			self.assertTrue(pattern.include)
+			self.assertIsNotNone(pattern.regex)
+
+
+if __name__ == '__main__':
+	unittest.main()