warn redundant casts doesn't work with `Protocol.__call__`

[graingert]

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.10&flags=strict%2Cwarn-redundant-casts&gist=bc9999020b0fb32610c0c3ec99a8568c

from typing import Protocol, cast

class FooType(Protocol):
 def __call__(self, ham: str) -> str:
 pass

def foo(ham: str) -> str:
 pass


v = cast(FooType, foo)
u: FooType = foo

Expected Behavior
I was expecting v = cast(FooType, foo) to work about the same as v: FooType = foo # type: ignore[assignment] with warn redundant ignores

Your Environment

See mypy-play

[graingert]

It seems even very simple redundant casts are not detected:

from typing import cast

class Foo:
 pass

class Bar(Foo):
 pass

v = cast(Foo, Bar())

https://mypy-play.net/?mypy=latest&python=3.10&flags=strict%2Cwarn-redundant-casts&gist=c166276e9623ced551d45e7a74d31510

[jhance]

Is the behavior with respect to subtyping documented?

[graingert]

The docs refer to casts that can be safely removed:

https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-warn-redundant-casts

This flag will make mypy report an error whenever your code uses an unnecessary cast that can safely be removed.