TypeAliasType does not recognize type parameter after use of Concatenate and cannot be subscripted

[Daraan]

Bug report

Bug description:

After using Concatenate to recursively replace a ParamSpec of a TypeAliasType, another subscription with a type param is possible but the type param is not recognized.

In the last part the following code (C2T = C2[T] # <--- should create a generic), however it's parameters are empty and it cannot be subscripted further:

Consider the following code sample, also availiable on pyright playground

from typing import TypeAliasType, Concatenate, ParamSpec, Any, TypeVar
from collections.abc import Callable

# (**P) -> str
type C[**P] = Callable[P, str]

T = TypeVar("T")
P2 = ParamSpec("P2")

# (int, **P2) -> str
C2 = C[Concatenate[int, P2]]

# OK
# (T) -> str
C1T = C[T]
# (str) -> str
C1_str = C1T[str]

# -------- 

# (int, T) -> str
C2T = C2[T] # <--- does not create a generic
print(C2T.__parameters__) # <-- is empty
# () 

# (int, str) -> str
C2_str = C2T[str] # <-- cannot be subscripted
# TypeError: C[(<class 'int'>, ~T)] is not a generic class

CPython versions tested on:

3.13

Operating systems tested on:

Linux

[tomasr8]

I think this will be fixed by this PR #124512
When I run your example on that branch, I get non-empty __parameters__:

>>> C2T = C2[T]
>>> C2T.__parameters__
(~T,)

[Eclips4]

Thanks for the investigation, Tomas.
So I guess we can close this as a duplicate of #124445?

[Daraan]

It's definitely similar, I'll close it and will check it later again. Thanks for checking!