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

@@ -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
 

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,

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(