Add comment in mypy/types.py

Author: ilevkivskyi

mypy/types.py

@@ -2416,6 +2416,8 @@ def __init__(
     ) -> None:
         super().__init__(line, column)
         if fallback.type and fallback.type.fullname == "builtins.tuple":
+            # We actively ignore type argument for plain tuple fallback, to avoid spurious errors,
+            # partial_fallback should never be used directly anyway, only via typeops.tuple_fallback().
             assert len(fallback.args) == 1
             if not isinstance(fallback.args[0], ProperType) or not isinstance(
                 fallback.args[0], AnyType