[1.16] Regression in inferring type via unittest.mock.Mock

[Dreamsorcerer]

Bug Report

Regression on type inference found in aiohttp:master.

Seems like the regression may be related to inheriting from Any (which mypy complains about, but is done in typeshed regardless, and has been for many years).

To Reproduce

This is a fairly minimal reproducer of the issue:

from typing import Any, Generic, Protocol, TypeVar
#from unittest.mock import Mock

_T = TypeVar("_T", covariant=True)

class Mock(Any):
    def __init__(self, **kwargs: Any) -> None: ...
    def __call__(self, *args: Any, **kwargs: Any) -> Any: ...


class _Factory(Protocol[_T]):
    def __call__(self, **kwargs: Any) -> _T: ...


class TraceConfig(Generic[_T]):
    def __init__(self, trace_config_ctx_factory: _Factory[_T]) -> None:
        ...

t = TraceConfig(Mock(return_value="foo"))

1.15 Behavior

(First error disappears if we actually import Mock.)

test.py:6: error: Class cannot subclass "Any" (has type "Any")  [misc]
Found 1 error in 1 file (checked 1 source file)

1.16 Behavior

test.py:6: error: Class cannot subclass "Any" (has type "Any")  [misc]
test.py:19: error: Need type annotation for "t"  [var-annotated]
Found 2 errors in 1 file (checked 1 source file)

[ilevkivskyi]

Hm, if subclassing Any is important here, I think there is a chance this is related to #8829 (on which I am going to work soon).

[ilevkivskyi]

Actually it looks like it was caused by #18587 because we consider that a class with fallback to any may be a metaclass. Maybe we can not do this here, since that special case was added specifically to ignore spurious Anys from type.__call__() IIRC. I will play with this.