Parameterized protocol structure ignored as argument

Bug Report

Parameterized protocols seem to be largely or totally ignored when specified as argument types. Simple example:

from typing import Protocol, TypeVar

T = TypeVar("T")
T_co = TypeVar("T_co", covariant=True)


class Proto(Protocol[T_co]):
    def __call__(self, *, a: str) -> T_co:
        ...


class InvalidClass:
    def __init__(self, *, a: int) -> None:
        ...


def test(b: Proto[T]) -> T:
    return b(a="0")
    

test(InvalidClass)  # <-- should fail type checking

InvalidClass is accepted here even though it does not conform to the protocol. Here's a more detailed playground gist.

As demonstrated in the gist, the issue does not reproduce when a function is provided, only with a class. It also does not manifest with assignment, only with arguments. However, assigning with the parameter set to Any also produces an unexpected result, which might somehow be related.

• Mypy version used: 1.0
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.11

まず、Python 3.11 上で mypy 1.0 を使って最小限の例を再現し、次にリンクされた playground の gist とその strict flags と比較します。Proto に準拠していないため mypy が test(InvalidClass) を拒否し、同時に関数と代入について報告された動作が維持されれば、修正は完了です。