Improve error message for --strict-concatenate

[hauntsaninja]

Resolves #13711, resolves #13429

[hauntsaninja]

cc @A5rocks

[A5rocks]

Looks alright to me. One big improvement would be fixing the error message for methods: original_caller_type.name is unexpected in that case.

To be specific, ATM the error message can be e.g. main.py:13: note: This may be because "inner of X" has arguments named: "x".

Reproducer (has other errors too):

from __future__ import annotations

from typing import Callable, Any
from typing_extensions import ParamSpec, Concatenate

_PRouteParams = ParamSpec("_PRouteParams")
def decorate_me(func: Callable[Concatenate[int, _PRouteParams], Any]) -> Callable[Concatenate[int, _PRouteParams], Any]:
    class X:
        def inner(x: int, *args: _PRouteParams.args, **kwargs: _PRouteParams.kwargs) -> dict[str, Any]:
            return {"result": func(x, *args, **kwargs)}

    return X.inner

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉