typeops: [minor] use CallableType.type_var_ids (#9694)

sobolevn · web-flow · commit 57c8317a92d3 · 2020-11-03T11:37:50.000-08:00
It is literally the same thing, but using `type_var_ids` is more ideomatic.
diff --git a/mypy/typeops.py b/mypy/typeops.py
@@ -235,7 +235,7 @@ class B(A): pass
             original_type = erase_to_bound(self_param_type)
         original_type = get_proper_type(original_type)
 
-        all_ids = [x.id for x in func.variables]
+        all_ids = func.type_var_ids()
         typeargs = infer_type_arguments(all_ids, self_param_type, original_type,
                                         is_supertype=True)
         if (is_classmethod
