Add isBackwardCompatibleWith for Argument and FunctionSchema (#23409)
Summary:
we intend to be conservative, and will relax the checks in future if necessary.
So far, we consider the following three conditions as backward compatible:
1) two schemas are equal
2) two schemas have same number of arguments, and this schema's
arguments are backward compatible with the corresponding ones in
argument list of old_schema.
3) this schema has m argument, old_argument has n argument, m > n.
the first n arguments of this schema are backward compatible with
the corresponding arguments of old_schema. the remaning arguments
must be either OptionalType or provide default values.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23409
ghstack-source-id: 90111021
Test Plan: buck test //caffe2/test:function_schema
Reviewed By: hl475
Differential Revision: D16505203
fbshipit-source-id: e4099537776a60e8945e5c3cd57fa861f3598a9b
