overload + decorator to transform callable into class protocol w/ attribute does not see the attribute #18715

from __future__ import annotations
from typing import overload, Callable, TypeVar, Protocol
from typing_extensions import ParamSpec, reveal_type

P = ParamSpec("P")
R = TypeVar("R", covariant=True)

class WithExtra(Protocol[P, R]):
    extra: str
    def __call__(self, *args: P.args, **kwargs: P.kwargs) -> R: ...

def add_extra(func: Callable[P, R]) -> WithExtra[P, R]:
    func.extra = "added"  # type: ignore
    return func  # type: ignore

@overload
@add_extra
def foo(x: int) -> str: ...

@overload
@add_extra
def foo(x: str) -> str: ...

@add_extra
def foo(x: int | str) -> str:
    return str(x)

assert foo.extra  # type: ignore[attr-defined]
reveal_type(foo)  # Revealed type is "Overload(def (x: builtins.int) -> builtins.str, def (x: builtins.str) -> builtins.str)"