Pass the type name to the messages method

Instead of inspecting the context, we directly pass the
type name to the messages methods as argument.

Author: David-Wobrock

mypy/checker.py

@@ -1483,8 +1483,9 @@ def erase_override(t: Type) -> Type:
                 for i in range(len(override.arg_types)):
                     if not is_subtype(original.arg_types[i],
                                       erase_override(override.arg_types[i])):
+                        type_name = override.definition.info.name()
                         self.msg.argument_incompatible_with_supertype(
-                            i + 1, name, name_in_super, supertype, node)
+                            i + 1, name, type_name, name_in_super, supertype, node)
                         emitted_msg = True
 
                 if not is_subtype(erase_override(override.ret_type),

mypy/messages.py

@@ -863,15 +863,14 @@ def signature_incompatible_with_supertype(
             name, target), context)
 
     def argument_incompatible_with_supertype(
-            self, arg_num: int, name: str, name_in_supertype: str,
-            supertype: str, context: Context) -> None:
+            self, arg_num: int, name: str, type_name: 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__":
-            assert isinstance(context, FuncDef)
-            multiline_msg = self.comparison_method_example_msg(class_name=context.info.name())
+            multiline_msg = self.comparison_method_example_msg(class_name=type_name)
             self.note_multiline(multiline_msg, context)
 
     def comparison_method_example_msg(self, class_name: str) -> str: