Sentinel and enum type merge issues with generic #22334

from typing_extensions import sentinel

Undefined = sentinel("Undefined")

def none_if_undefined[_T](value: _T | Undefined) -> _T | None:
    return None if value is Undefined else value

def func() -> None:
    device_id: str | Undefined | None = Undefined
    device_id = none_if_undefined(device_id)  # <-- error
    reveal_type(device_id)

test.py:10: error: Argument 1 to "none_if_undefined" has incompatible type "str | Undefined | None"; expected "str | Undefined"  [arg-type]
test.py:11: note: Revealed type is "str | Undefined | None"

def func() -> None:
    device_id: str | Undefined | None = Undefined
    x = none_if_undefined(device_id)
    reveal_type(x)
    device_id = x
    reveal_type(device_id)

test.py:11: note: Revealed type is "str | None"
test.py:13: note: Revealed type is "str | None"

from enum import Enum
from typing import Literal

class E(Enum):
    SPECIAL = 1

def none_if_special[_T](value: _T | Literal[E.SPECIAL]) -> _T | None:
    return None if value is E.SPECIAL else value

def func() -> None:
    device_id: str | Literal[E.SPECIAL] | None = E.SPECIAL
    device_id = none_if_special(device_id)  # <-- error
    reveal_type(device_id)

test.py:12: error: Argument 1 to "none_if_special" has incompatible type "str | Literal[E.SPECIAL] | None"; expected "str | Literal[E.SPECIAL]"  [arg-type]
test.py:13: note: Revealed type is "str | Literal[test7.E.SPECIAL] | None"

def none_if_int[_T](value: _T | int) -> _T | None:
    return None if isinstance(value, int) else value

def func() -> None:
    device_id: str | int | None = 42
    device_id = none_if_int(device_id)
    reveal_type(device_id)