Signature of decorated function is not type checked by mypy

[truenicoco]

The following has mypy (expectedly) failing with error: Argument 1 to "f1" has incompatible type "int"; expected "str" [arg-type]

async def f1(x: str, y: int) -> str:
    return x + str(y)


async def main():
    await f1(1, 1)

But decorating f1 with @alru_cache prevents mypy from detecting any issue.

[Dreamsorcerer]

Yes, it currently only types the return type correctly. It would need updating to use ParamSpec to type check the parameters.

[Dreamsorcerer]

I've started #508 for this, but it's not working for methods correctly, not sure what's gone wrong there. It also results in type errors for partial() as mypy/typeshed don't fully support it yet.

If anyone wants to try and make any fixes, that'd be great.

[rkjdid]

may be related https://youtrack.jetbrains.com/issue/PY-23067/Pycharm-not-picking-function-metadata-from-functools.wraps-with-methods#focus=Comments-27-6431674.0-0

I was having issues like this with (some) decorators in jetbrain's ide, the "preserved_signature" decorator on decorator fixes it