From 3d8dd06423bc5a9fba82bc0e8cb369363cadfabf Mon Sep 17 00:00:00 2001
From: chuenchen309 <48723787+chuenchen309@users.noreply.github.com>
Date: Thu, 16 Jul 2026 23:13:18 +0800
Subject: [PATCH] Fix --write-changes silently not fixing a trailing-apostrophe
 typo

The word regex admits a trailing apostrophe, so word can end in one. A
\b after that can never hold -- it needs a word/non-word transition and
the apostrophe is already non-word -- so re.sub matched nothing while
codespell still reported FIXED and exited 0.

Use lookarounds instead, and escape the interpolated word.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 codespell_lib/_codespell.py       |  7 ++++++-
 codespell_lib/tests/test_basic.py | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/codespell_lib/_codespell.py b/codespell_lib/_codespell.py
index 994c5c4a66..bb3377e908 100644
--- a/codespell_lib/_codespell.py
+++ b/codespell_lib/_codespell.py
@@ -1094,7 +1094,12 @@ def parse_lines(
 
                 if options.write_changes and fix:
                     changed = True
-                    lines[i] = re.sub(rf"\b{word}\b", fixword, lines[i])
+                    # Not \b: the word regex admits a trailing apostrophe, and a
+                    # \b after one can never hold, so the substitution silently
+                    # matched nothing.
+                    lines[i] = re.sub(
+                        rf"(?<!\w){re.escape(word)}(?!\w)", fixword, lines[i]
+                    )
                     fixed_words.add(word)
                     changes_made.append((line_number + 1, word, fixword))
                     continue
diff --git a/codespell_lib/tests/test_basic.py b/codespell_lib/tests/test_basic.py
index 930f09f14a..664321d395 100644
--- a/codespell_lib/tests/test_basic.py
+++ b/codespell_lib/tests/test_basic.py
@@ -216,6 +216,22 @@ def test_default_word_parsing(
     assert cs.main(fname) == 1, "misspelling containing typographic apostrophe U+2019"
 
 
+def test_write_changes_trailing_apostrophe(
+    tmp_path: Path,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    """A misspelling ending in an apostrophe must actually be written out."""
+    fname = tmp_path / "trailing_apostrophe"
+
+    fname.write_text("dont' go\n", encoding="utf-8")  # U+0027
+    cs.main("-w", fname, count=False)
+    assert fname.read_text(encoding="utf-8") == "don't go\n"
+
+    fname.write_text("dont’ go\n", encoding="utf-8")  # U+2019  # noqa: RUF001
+    cs.main("-w", fname, count=False)
+    assert fname.read_text(encoding="utf-8") == "don’t go\n"  # noqa: RUF001
+
+
 def test_bad_glob(
     tmp_path: Path,
     capsys: pytest.CaptureFixture[str],