Generic cached return value cannot be converted to declared value even when they are the same type

[jzazo]

Describe the bug
I declare a generic return type, and I have a provider of that same return type, but cached. Mypy does not declare an error but Pyright raises one. If I remove the caching no error is reported.

I raised this issue in pyright's repo. @erictraut stated that cache method does not maintain the signature of the function it's decorating. This other issue might be related.

Code

from abc import abstractmethod
from functools import cache
from typing import Any, Generic, Protocol, TypeVar

from typing_extensions import NamedTuple

T = TypeVar("T")
T_co = TypeVar("T_co", covariant=True)

class ServiceId(NamedTuple, Generic[T]):
    id: str

class Provider(Protocol[T_co]):
    @abstractmethod
    def __call__(self) -> T_co:
        ...

class Servicer:
    _d: dict[str, Any]

    @cache  # commenting this line removes the error
    def get_service(self, service_id: ServiceId[T]) -> T:
        return self._d[service_id.id]

    def get_provider(self, service_id: ServiceId[T]) -> Provider[T]:
        return lambda: self.get_service(service_id)  # Expression of type "() -> T@get_service" cannot be assigned to return type "Provider[T@get_provider]"

[srittau]

Looks to be a duplicate of #11280.