Callable type is reported as not callable when used as a decorator

[sobolevn]

Example:

from typing import Callable, Union, Any, overload, Protocol

class DCall(Protocol):
    def __call__(self, arg: Union[int, str]) -> None:
        ...

class D:
    def __getattr__(self, attr: str) -> DCall:
        # This method might contain something like during runtime:
        # if attr == '__call__':
        #     return some_func
        # assert False
        ...

def dec_d(f: Callable[..., Any]) -> D:
    return D()

@overload
def f_d(arg: int) -> None: ...
@overload
def f_d(arg: str) -> None: ...
@dec_d
def f_d(arg: Union[int, str]) -> None: ...

Outputs:

out/ex.py:18: error: "D" not callable

This happens here:

mypy/mypy/checker.py

Lines 510 to 520 in 4f59ca4

	if inner_type is not None and not isinstance(inner_type, AnyType):
	if isinstance(inner_type, CallableType):
	impl_type = inner_type
	elif isinstance(inner_type, Instance):
	inner_call = get_proper_type(
	find_member('__call__', inner_type, inner_type, is_operator=True)
	)
	if isinstance(inner_call, CallableType):
	impl_type = inner_call
	if impl_type is None:
	self.msg.not_callable(inner_type, defn.impl)

Refs #11638
Refs #11630

[sobolevn]

Mypy is right here. See #11638 (review)