Quoted type aliases not understood

[sterliakov]

Summary

Check the following code:

from typing import TypeAlias

Foo: TypeAlias = "int | str"
Bar: TypeAlias = int | str

x: Foo = 0  # Fails
y: Bar = 0  # OK

Output of uvx ty check a.py --output-format concise (without any config files, in a fresh mktemp -d with the above snippet cat'd into a.py):

error[invalid-type-form] a.py:6:4: Variable of type `Literal["int | str"]` is not allowed in a type expression
Found 1 diagnostic

playground link

As per the spec, quotes should be ignored in the RHS, it is not a literal definition:)

This isn't a toy problem - quoted RHS is the most convenient way to define a recursive alias (at least prior to PEP695, but I'd personally use this on 3.12+ too) or make it dependent on TYPE_CHECKING-only imports.

Foo: TypeAlias = "int | Iterable[Foo]"

Version

0.0.1-alpha.14

[sharkdp]

Thank you for reporting this. We do not support typing.TypeAlias yet, see #544. Once we do, it will also (automatically) support stringified annotations.

Stringified annotations are already supported in other places where type expressions are expected: https://play.ty.dev/5dbc7ee3-7b68-4498-9424-224baad866a1

type IntOrStr = "int | str"

def _(x: "int | str", y: IntOrStr):
    reveal_type(x)  # int | str
    reveal_type(y)  # int | str

    x = 1
    y = 1

[carljm]

Confirmed that this will be fixed by astral-sh/ruff#21394