Reject TypedDict with invalid name argument (#3614)

Author: JukkaL

mypy/semanal.py

@@ -2343,6 +2343,10 @@ def check_typeddict(self, node: Expression, var_name: str = None) -> Optional[Ty
             info = self.build_typeddict_typeinfo('TypedDict', [], [], set())
         else:
             name = cast(StrExpr, call.args[0]).value
+            if var_name is not None and name != var_name:
+                self.fail(
+                    "First argument '{}' to TypedDict() does not match variable name '{}'".format(
+                        name, var_name), node)
             if name != var_name or self.is_func_scope():
                 # Give it a unique name derived from the line number.
                 name += '@' + str(call.line)

test-data/unit/check-typeddict.test

@@ -1069,6 +1069,11 @@ from mypy_extensions import TypedDict
 Point = TypedDict('Point', {'x': 1, 'y': 1})  # E: Invalid field type
 [builtins fixtures/dict.pyi]
 
+[case testCannotCreateTypedDictTypeWithInvalidName]
+from mypy_extensions import TypedDict
+X = TypedDict('Y', {'x': int})  # E: First argument 'Y' to TypedDict() does not match variable name 'X'
+[builtins fixtures/dict.pyi]
+
 
 -- Special cases