Report protocol problems in no_variant_matches_arguments if possible

Feature

Report protocol problems in no_variant_matches_arguments if possible.

Pitch

Given following example:

from typing import Protocol, overload


class Foo(Protocol):
    def some_method(self, value: int = 0) -> None: ...


class Bar:
    def some_method(self, value: int) -> None:
        pass


@overload
def accept_foo(value: Foo, v: int) -> None:
    pass


@overload
def accept_foo(value: Foo, v: float) -> None:
    pass


def accept_foo(value: Foo, v: int | float) -> None:
    pass


accept_foo(Bar(), 1)

The Bar has conflict with the Protocol Foo, but currently Mypy won't report the protocol problems. This is the current error report:

protocol_example.py:27: error: No overload variant of "accept_foo" matches argument types "Bar", "int"  [call-overload]
protocol_example.py:27: note: Possible overload variants:
protocol_example.py:27: note:     def accept_foo(value: Foo, v: int) -> None
protocol_example.py:27: note:     def accept_foo(value: Foo, v: float) -> None
Found 1 error in 1 file (checked 1 source file)

If we can report the protocol problems in this case, it may save developers time to figure out what' wrong.

I did a proof-of-concept implementation here: https://github.com/python/mypy/commit/a2040d3680320afbac6e13b3b04593a7965242bc. This is the updated error report:

protocol_example.py:27: error: No overload variant of "accept_foo" matches argument types "Bar", "int"  [call-overload]
protocol_example.py:27: note: Following member(s) of "Bar" have conflicts:
protocol_example.py:27: note:     Expected:
protocol_example.py:27: note:         def some_method(self, value: int = ...) -> None
protocol_example.py:27: note:     Got:
protocol_example.py:27: note:         def some_method(self, value: int) -> None
protocol_example.py:27: note:     Expected:
protocol_example.py:27: note:         def some_method(self, value: int = ...) -> None
protocol_example.py:27: note:     Got:
protocol_example.py:27: note:         def some_method(self, value: int) -> None
protocol_example.py:27: note: Possible overload variants:
protocol_example.py:27: note:     def accept_foo(value: Foo, v: int) -> None
protocol_example.py:27: note:     def accept_foo(value: Foo, v: float) -> None
Found 1 error in 1 file (checked 1 source file)

If this is OK, I'd happy to refine the implementation and submit a PR.

Thanks.

Start at the no_variant_matches_arguments entry point and review the proof-of-concept commit linked in the issue. Reproduce the supplied Protocol and overload example, then verify that the diagnostic reports the conflicting members accurately without duplicate or misleading output.