(🐞) Error when using new union syntax and TypeVar in generic TypeAlias

[KotlinIsland]

Originally spotted by @Eldar1205

from typing import *
T = TypeVar("T")

A: TypeAlias = Union[T, int] 
B: TypeAlias = T | int  # error

[JelleZijlstra]

This isn't an error; it creates a generic alias.

[KotlinIsland]

from typing import *
T = TypeVar("T")

A: TypeAlias = list[T]  # no error

def foo(a: A) -> A: ...

reveal_type(foo([1]))  # list[Any]

Well something seems broken

[KotlinIsland]

Also these forms are then inconsistent:

A: TypeAlias = T | None  # error
B: TypeAlias = T  # error

[JelleZijlstra]

Your first example produces main.py:6: error: Missing type parameters for generic type "A" with --disallow-any-generics. Agree that the T | None case should be accepted.

[KotlinIsland]

@JelleZijlstra Fair enough, thanks for explaining. I've updated the title and OP, want to reopen it?

[AlexWaygood]

Agree that the T | None case should be accepted.

That one's a PEP 604 bug; it works fine with typing.Union. https://mypy-play.net/?mypy=latest&python=3.10&gist=440bf42209bcc85bd6faa7b03b7e23d7

And it's already been reported in a different issue, lemme just find it

[AlexWaygood]

Here: #12211