(🎁) Error messages for decorator applications have a very bad UX

from typing import Callable

def decorator(f: object) -> Callable[[Callable[[int], object]], None]: ...

def f(a: int) -> None: ...

@decorator(f)  # error: Argument 1 has incompatible type "Callable[[], Any]"; expected "Callable[[int], object]"  [arg-type]
def something(): ...

So the error is that the function something doesn't have the right type for the decorator, but the message is quite misleading, it reads like the error is with the call to decorator and f.

Start by reproducing the diagnostic with the decorator example in the issue and trace how mypy reports the decorator application. No source file or test is named, so locating the relevant diagnostic and deciding the intended wording will require exploring the type-checker implementation. Done means the error clearly identifies the incompatible function being decorated rather than implying a problem with the decorator call.