Fix a crash on missing self with --check-untyped-defs (#7669)

Author: ilevkivskyi

mypy/typeops.py

@@ -400,7 +400,7 @@ def function_type(func: FuncBase, fallback: Instance) -> FunctionLike:
 def callable_type(fdef: FuncItem, fallback: Instance,
                   ret_type: Optional[Type] = None) -> CallableType:
     # TODO: somewhat unfortunate duplication with prepare_method_signature in semanal
-    if fdef.info and not fdef.is_static:
+    if fdef.info and not fdef.is_static and fdef.arg_names:
         self_type = fill_typevars(fdef.info)  # type: Type
         if fdef.is_class or fdef.name() == '__new__':
             self_type = TypeType.make_normalized(self_type)

test-data/unit/check-classes.test

@@ -6319,3 +6319,10 @@ class Foo:
 reveal_type(Foo().x)  # N: Revealed type is 'Union[Any, None]'
 reveal_type(Foo().y)  # N: Revealed type is 'builtins.list[Any]'
 [builtins fixtures/list.pyi]
+
+[case testCheckUntypedDefsSelf3]
+# flags: --check-untyped-defs
+
+class Foo:
+    def bad():  # E: Method must have at least one argument
+        self.x = 0  # E: Name 'self' is not defined