[match-case]/[isinstance] narrowing logic against the special `AnyCallable` Protocol differs from `callable()` check

[randolf-scholz]

According to the typing spec (https://typing.python.org/en/latest/spec/callables.html#meaning-of-in-callable),

@runtime_checkable
class AnyCallable(Protocol):
    def __call__(self, *args: Any, **kwargs: Any) -> Any: ...

is an implementation of Callable[..., Any]. Therefore, its isinstance-narrowing and match-case class pattern narrowing should behave the same as a simple if callable() narrowing. However, this is not the case: both isinstance and match-case produce different results:

from typing import Any, Callable
from typing_extensions import Protocol, runtime_checkable, assert_type

@runtime_checkable
class AnyCallable(Protocol):
    def __call__(self, *args: Any, **kwargs: Any) -> Any: ...

def check_proto(p: AnyCallable) -> None:
    assert_type(p, Callable[..., Any])

class FnImpl:
    def __call__(self, x: object, /) -> int: ...

# Test Baseline
def test_iscallable_object(x: object) -> None:
    if callable(x):
        reveal_type(x)  # N: Revealed type is "__main__.<callable subtype of object>"

def test_iscallable_impl(x: FnImpl) -> None:
    if callable(x):
        reveal_type(x)  # N: Revealed type is "__main__.FnImpl"

def test_iscallable_callable(x: Callable[[object], int]) -> None:
    if callable(x):
        reveal_type(x)  # N: Revealed type is "def (builtins.object) -> builtins.int"


# Test isinstance
def test_isinstance_object(x: object) -> None:
    if isinstance(x, AnyCallable):
        reveal_type(x)  # N: Revealed type is "__main__.AnyCallable"

def test_isinstance_impl(x: FnImpl) -> None:
    if isinstance(x, AnyCallable):
        reveal_type(x)  # N: Revealed type is "__main__.FnImpl"

def test_isinstance_callable(x: Callable[[object], int]) -> None:
    if isinstance(x, AnyCallable):
        reveal_type(x)  # N: Revealed type is "__main__.AnyCallable"


# test match-case
def test_match_object(x: object) -> None:
    match x:
        case AnyCallable() as fn:
            reveal_type(fn)  # N: Revealed type is "__main__.AnyCallable"

def test_match_impl(x: FnImpl) -> None:
    match x:
        case AnyCallable() as fn:
            reveal_type(fn)  # N: Revealed type is "__main__.AnyCallable"

def test_match_callable(x: Callable[[object], int]) -> None:
    match x:
        case AnyCallable() as fn:
            reveal_type(fn)  # N: Revealed type is "__main__.AnyCallable"

https://mypy-play.net/?mypy=latest&python=3.12&gist=5cb05553fa6674d445906eda99802e90