From 24e4cb20ab03c20af390fec7303207af2a4a09e8 Mon Sep 17 00:00:00 2001
From: GiGaGon <107241144+MeGaGiGaGon@users.noreply.github.com>
Date: Thu, 5 Jun 2025 18:49:15 -0700
Subject: [PATCH] Fix backslash cr nl bug (#4673)

* Update tokenize.py

* Update CHANGES.md

* Update test_black.py

* Update test_black.py

* Update test_black.py
---
 CHANGES.md                     |  1 +
 src/blib2to3/pgen2/tokenize.py | 12 +++++++++++-
 tests/test_black.py            | 20 ++++++++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index cf415f1..ae8bb78 100644
--- 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 on a `\\r\n` (#4673)
 
 ### Preview style
 
diff --git a/src/blib2to3/pgen2/tokenize.py b/src/blib2to3/pgen2/tokenize.py
index 5cbfd51..46c4319 100644
--- a/src/blib2to3/pgen2/tokenize.py
+++ b/src/blib2to3/pgen2/tokenize.py
@@ -113,7 +113,17 @@ def transform_whitespace(
         and prev_token.type not in (TokenType.nl, TokenType.newline)
     ):
         token_str = source[token.start_index : token.end_index]
-        if token_str.startswith("\\\n"):
+        if token_str.startswith("\\\r\n"):
+            return pytokens.Token(
+                TokenType.nl,
+                token.start_index,
+                token.start_index + 3,
+                token.start_line,
+                token.start_col,
+                token.start_line,
+                token.start_col + 3,
+            )
+        elif token_str.startswith("\\\n") or token_str.startswith("\\\r"):
             return pytokens.Token(
                 TokenType.nl,
                 token.start_index,
diff --git a/tests/test_black.py b/tests/test_black.py
index ee026f3..4588add 100644
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -2065,6 +2065,26 @@ 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:
+        # 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
+        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"
+        assert (
+            black.format_str("class A\\\r\n:...", mode=black.FileMode())
+            == "class A: ...\n"
+        )
+        assert (
+            black.format_str("class A\\\n:...", mode=black.FileMode())
+            == "class A: ...\n"
+        )
+        assert (
+            black.format_str("class A\\\r:...", mode=black.FileMode())
+            == "class A: ...\n"
+        )
+
 
 class TestCaching:
     def test_get_cache_dir(