Paramspec, protocol and classmethod

[mehdigmira]

Bug Report

Mypy doesn't infer the right type in the following example.

To Reproduce

https://gist.github.com/94a0c6c7b64ea26e03b9a44ae460c6cb

Expected Behavior

mypy infers Type of "Add.async_func()" is "(x: int, y: int) -> int" as pyright does

Actual Behavior

mypy infers Revealed type is "def (*<nothing>, **<nothing>) -> builtins.int"

Your Environment

• Mypy version used: 0.981
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.7

[AlexWaygood]

So that others don't have to click through, here's the snippet:

from typing import TypeVar, Protocol, Type, Callable
from typing_extensions import ParamSpec

ReturnT = TypeVar("ReturnT", covariant=True)
P = ParamSpec("P")

class AsyncP(Protocol[P]):

    def __init__(self, *args: P.args, **kwargs: P.kwargs) -> None:
        ...

    
class Async:

    @classmethod
    def async_func(cls: Type[AsyncP[P]]) -> Callable[P, int]:
        ...


class Add(Async):

    def __init__(self, x: int, y: int) -> None:
        self.x = x
        self.y = y

        
reveal_type(Add.async_func())

And here's a link to mypy playground: https://mypy-play.net/?mypy=latest&python=3.11&gist=34604ea95d10df9b6bcf2de46e8383a2

[ilevkivskyi]

Note that part of the problem is that you are using __init__ in protocol, which is very special, see #15844. The other part of the problem will be fixed by #15903

[hauntsaninja]

@mehdigmira is the project you were running into this on open source?

[mehdigmira]

No the project is not open source