Do not display __eq__ note when not function definition

Author: David-Wobrock

mypy/checker.py

@@ -1476,10 +1476,9 @@ def check_override(self, override: FunctionLike, original: FunctionLike,
                 # are erased, then it is definitely an incompatibility.
 
                 override_ids = override.type_var_ids()
+                type_name = None
                 if isinstance(override.definition, FuncDef):
                     type_name = override.definition.info.name()
-                else:
-                    type_name = "Foo"
 
                 def erase_override(t: Type) -> Type:
                     return erase_typevars(t, ids_to_erase=override_ids)

mypy/messages.py

@@ -863,13 +863,13 @@ def signature_incompatible_with_supertype(
             name, target), context)
 
     def argument_incompatible_with_supertype(
-            self, arg_num: int, name: str, type_name: str,
+            self, arg_num: int, name: str, type_name: Optional[str],
             name_in_supertype: str, supertype: str, context: Context) -> None:
         target = self.override_target(name, name_in_supertype, supertype)
         self.fail('Argument {} of "{}" incompatible with {}'
                   .format(arg_num, name, target), context)
 
-        if name == "__eq__":
+        if name == "__eq__" and type_name:
             multiline_msg = self.comparison_method_example_msg(class_name=type_name)
             self.note_multiline(multiline_msg, context)