Fix backslash carriage return comments (psf#4663)

MeGaGiGaGon · JelleZijlstra · cobaltt7 · web-flow · commit 60d734a84d5c · 2025-06-22T14:14:11.000-05:00
* Update comments.py * Update CHANGES.md * Update test_black.py * Update tests/test_black.py Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com> * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com> Co-authored-by: cobalt <61329810+cobaltt7@users.noreply.github.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
diff --git a/CHANGES.md b/CHANGES.md
@@ -16,6 +16,7 @@
 - Handle `# fmt: skip` followed by a comment at the end of file (#4635)
 - Fix crash when a tuple appears in the `as` clause of a `with` statement (#4634)
 - Fix crash when tuple is used as a context manager inside a `with` statement (#4646)
+- Fix crash when formatting a `\` followed by a `\r` followed by a comment (#4663)
 - Fix crash on a `\\r\n` (#4673)
 - Fix crash on `await ...` (where `...` is a literal `Ellipsis`) (#4676)
 - Remove support for pre-python 3.7 `await/async` as soft keywords/variable names
diff --git a/src/black/comments.py b/src/black/comments.py
@@ -88,7 +88,7 @@ def list_comments(prefix: str, *, is_endmarker: bool) -> list[ProtoComment]:
     nlines = 0
     ignored_lines = 0
     form_feed = False
-    for index, full_line in enumerate(re.split("\r?\n", prefix)):
+    for index, full_line in enumerate(re.split("\r?\n|\r", prefix)):
         consumed += len(full_line) + 1  # adding the length of the split '\n'
         match = re.match(r"^(\s*)(\S.*|)$", full_line)
         assert match
diff --git a/tests/test_black.py b/tests/test_black.py
@@ -2048,10 +2048,20 @@ def test_lines_with_leading_tabs_expanded(self) -> None:
         assert lines_with_leading_tabs_expanded("\t\tx") == [f"{tab}{tab}x"]
         assert lines_with_leading_tabs_expanded("\tx\n  y") == [f"{tab}x", "  y"]
 
-    def test_backslash_carriage_return(self) -> None:
+    def test_carriage_return_edge_cases(self) -> None:
         # These tests are here instead of in the normal cases because
         # of git's newline normalization and because it's hard to
-        # get `\r` vs `\r\n` vs `\n` to display properly in editors
+        # get `\r` vs `\r\n` vs `\n` to display properly
+        assert (
+            black.format_str(
+                "try:\\\r# type: ignore\n pass\nfinally:\n pass\n",
+                mode=black.FileMode(),
+            )
+            == "try:  # type: ignore\n    pass\nfinally:\n    pass\n"
+        )
+        assert black.format_str("{\r}", mode=black.FileMode()) == "{}\n"
+        assert black.format_str("pass #\r#\n", mode=black.FileMode()) == "pass  #\n#\n"
+
         assert black.format_str("x=\\\r\n1", mode=black.FileMode()) == "x = 1\n"
         assert black.format_str("x=\\\n1", mode=black.FileMode()) == "x = 1\n"
         assert black.format_str("x=\\\r1", mode=black.FileMode()) == "x = 1\n"
