Allow `NotRequired[]` to be passed as a `TypeVar`

I just found myself wanting to do the following:

from typing import TypedDict, NotRequired, Generic, TypeVar, Union, Never

_T = TypeVar('_T')

Foo = Union['FooSub1[_T]', 'FooSub2[_T]', 'FooSub3[_T]']

class BaseFoo(TypedDict, Generic[_T]):
    bar: _T

class FooSub1(BaseFoo[_T]):
    sub1: str

class FooSub2(BaseFoo[_T]):
    sub2: str

class FooSub3(BaseFoo[_T]):
    sub3: str

def foo(foo_with_bar: Foo[int]):
    reveal_type(foo_with_bar) # Type of "foo_with_bar" is "FooSub1[int] | FooSub2[int] | FooSub3[int]"

def bar(foo_without_bar: Foo[NotRequired[Never]]): # error: "NotRequired" is not allowed in this context
    pass

Mypy and Pyright both disallow NotRequired to be passed as a TypeVar. However the only way to avoid doing that would require me to duplicate all subclass definitions, which I am not willing to do because I have more than a dozen and so much duplication would make the code less maintainable.

Commencez par le reproducteur de l’issue et comparez les règles actuelles de NotRequired et TypeVar dans mypy et Pyright, les deux checkers nommés dans le rapport. Aucun fichier ni test n’est identifié ; le travail serait terminé lorsqu’une conception des règles de typage et un comportement correspondant des checkers seraient convenus, sans dupliquer les sous-classes de TypedDict.