Fixes issue #17840 (shows signature of __call__ for incompatible function argument)

[aybdee]

Fixes issue #17840 (shows signature of call for incompatible function argument)
made modifications to messages.py

• created a note_call_message function to just return the note message for call type instead of emitting the note
• implemented changes to fix issue If Callable type is incompatible with a callable protocol, show signature of __call__ #17840

wrote one unit test in check-callable:testCallableSubtypingTrivialSuffix

[aybdee]

also added added notes to some tests in check-inference.test and check-protocols.test

[brianschubert]

Hmm, this seems to duplicate some logic that's already in incompatible_argument_note, which is called immediately after incompatible_argument. I think a simpler fix would be possible by tweaking incompatible_argument_note instead.

This also seems to be taking the signature from the wrong type. Take for example this test:

[case testCallableImplementsProtocolGenericNotGeneric]
from typing import Protocol, TypeVar, Tuple

T = TypeVar('T')

class Caller(Protocol):
    def __call__(self, x: int) -> int: ...

def call(x: T) -> T: ...

def bad(x: T) -> Tuple[T, T]: ...

def func(caller: Caller) -> None:
    pass

func(call)
func(bad)  # E: Argument 1 to "func" has incompatible type "Callable[[T], Tuple[T, T]]"; expected "Caller" \
           # N: "Caller.__call__" has type "Callable[[Arg(T, 'x')], Tuple[T, T]]"

Here it's displaying the signature of bad instead of Caller.__call__. I would have expected N: "Caller.__call__" has type "Callable[[Arg(int, 'x')], int]

[aybdee]

Thank you for the feedback, i've implemented the changes

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sphinx (https://github.com/sphinx-doc/sphinx)
+ sphinx/application.py:1093:38: note: "RoleFunction.__call__" has type "Callable[[str, str, str, int, Inliner, DefaultArg(dict[str, Any] | None, 'options'), DefaultArg(Sequence[str], 'content')], tuple[list[Node], list[system_message]]]"

werkzeug (https://github.com/pallets/werkzeug)
+ tests/test_formparser.py:436: note: "TStreamFactory.__call__" has type "Callable[[Arg(int | None, 'total_content_length'), Arg(str | None, 'content_type'), Arg(str | None, 'filename'), DefaultArg(int | None, 'content_length')], IO[bytes]]"