Fix crash on type comment with trailing space

CHANGES.md

@@ -17,6 +17,8 @@
   PEP 604 unions (#3735)
 - Fix a bug where multi-line open parenthesis magic comment like `type: ignore` were not
   correctly parsed (#3740)
+- Fix error in AST validation when Black removes trailing whitespace in a type comment
+  (#3773)
 
 ### Preview style
 

src/black/parsing.py

@@ -208,15 +208,18 @@ def stringify_ast(node: ast.AST, depth: int = 0) -> Iterator[str]:
 
         else:
             normalized: object
-            # Constant strings may be indented across newlines, if they are
-            # docstrings; fold spaces after newlines when comparing. Similarly,
-            # trailing and leading space may be removed.
             if (
                 isinstance(node, ast.Constant)
                 and field == "value"
                 and isinstance(value, str)
             ):
+                # Constant strings may be indented across newlines, if they are
+                # docstrings; fold spaces after newlines when comparing. Similarly,
+                # trailing and leading space may be removed.
                 normalized = _normalize("\n", value)
+            elif field == "type_comment" and isinstance(value, str):
+                # Trailing whitespace in type comments is removed.
+                normalized = value.rstrip()
             else:
                 normalized = value
             yield f"{'  ' * (depth+2)}{normalized!r},  # {value.__class__.__name__}"

tests/data/simple_cases/comments2.py

@@ -154,6 +154,9 @@ def _init_host(self, parsed) -> None:
                 not parsed.hostname.strip()):
             pass
 
+
+a = "type comment with trailing space"  # type: str   
+
 #######################
 ### SECTION COMMENT ###
 #######################
@@ -332,6 +335,8 @@ def _init_host(self, parsed) -> None:
             pass
 
 
+a = "type comment with trailing space"  # type: str
+
 #######################
 ### SECTION COMMENT ###
 #######################