Missing TypeIs narrowing with covariant generic

Mypy fails to narrow away an Any-specialized covariant generic after TypeIs narrowing to its object specialization:

from typing import Any, Generic, TypeVar
from typing_extensions import TypeIs

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

class Source(Generic[T_co]): ...

def is_source(x: object) -> TypeIs[Source[object]]:
    return False

def f(x: int | Source[Any]) -> None:
    assert not is_source(x)
    reveal_type(x)  # expect int, mypy reveals int | Source[Any]

In contrast this does work correctly with an analogous contravariant type:

from typing import Any, Generic, TypeVar
from typing_extensions import Never, TypeIs

T_contra = TypeVar("T_contra", contravariant=True)

class Sink(Generic[T_contra]): ...

def is_sink(x: object) -> TypeIs[Sink[Never]]:
    return False

def f(x: int | Sink[Any]) -> None:
    assert not is_sink(x)
    reveal_type(x)  # int

(Found in python/typeshed#15931.)

Usa lo snippet Python minimo presente nell’issue come riproduttore, quindi confronta il narrowing covariante di Source[Any] con il caso contravariante funzionante di Sink[Never]. Il lavoro è completato quando reveal_type(x) è int dopo assert not is_source(x), preservando il comportamento esistente di Sink.