Support files with type comment syntax errors

CHANGES.md

@@ -29,6 +29,8 @@
 
 <!-- Changes to the parser or to version autodetection -->
 
+- Added support for formatting files with invalid type comments (#3594)
+
 ### Performance
 
 <!-- Changes that improve Black's performance. -->

src/black/parsing.py

@@ -148,24 +148,29 @@ def lib2to3_unparse(node: Node) -> str:
 
 
 def parse_single_version(
-    src: str, version: Tuple[int, int]
+    src: str, version: Tuple[int, int], type_comments: bool
 ) -> Union[ast.AST, ast3.AST]:
     filename = "<unknown>"
     # typed-ast is needed because of feature version limitations in the builtin ast 3.8>
     if sys.version_info >= (3, 8) and version >= (3,):
-        return ast.parse(src, filename, feature_version=version, type_comments=True)
+        return ast.parse(
+            src, filename, feature_version=version, type_comments=type_comments
+        )
 
     if _IS_PYPY:
         # PyPy 3.7 doesn't support type comment tracking which is not ideal, but there's
         # not much we can do as typed-ast won't work either.
         if sys.version_info >= (3, 8):
-            return ast3.parse(src, filename, type_comments=True)
+            return ast3.parse(src, filename, type_comments=type_comments)
         else:
             return ast3.parse(src, filename)
     else:
-        # Typed-ast is guaranteed to be used here and automatically tracks type
-        # comments separately.
-        return ast3.parse(src, filename, feature_version=version[1])
+        if type_comments:
+            # Typed-ast is guaranteed to be used here and automatically tracks type
+            # comments separately.
+            return ast3.parse(src, filename, feature_version=version[1])
+        else:
+            return ast.parse(src, filename)
 
 
 def parse_ast(src: str) -> Union[ast.AST, ast3.AST]:
@@ -175,11 +180,17 @@ def parse_ast(src: str) -> Union[ast.AST, ast3.AST]:
     first_error = ""
     for version in sorted(versions, reverse=True):
         try:
-            return parse_single_version(src, version)
+            return parse_single_version(src, version, type_comments=True)
         except SyntaxError as e:
             if not first_error:
                 first_error = str(e)
 
+            # Try to parse without type comments
+            try:
+                return parse_single_version(src, version, type_comments=False)
+            except SyntaxError:
+                pass
+
     raise SyntaxError(first_error)
 
 

tests/data/type_comments/type_comment_syntax_error.py

@@ -0,0 +1,11 @@
+def foo(
+    # type: Foo
+    x): pass
+
+# output
+
+def foo(
+    # type: Foo
+    x,
+):
+    pass

tests/test_black.py

@@ -1938,6 +1938,14 @@ def test_equivalency_ast_parse_failure_includes_error(self) -> None:
         err.match("invalid character")
         err.match(r"\(<unknown>, line 1\)")
 
+    def test_type_comment_syntax_error(self) -> None:
+        """
+        Test that black is able to format python code with type comment syntax errors.
+        """
+        source, expected = read_data("type_comments", "type_comment_syntax_error")
+        assert_format(source, expected)
+        black.assert_equivalent(source, expected)
+
 
 class TestCaching:
     def test_get_cache_dir(