Generic with ParamSpec and Concatenate substitutions behave incorrectly

[Daraan]

The following code displays some incorrect behavior, but different parts do not work in certain ranges of 3.8-3.11.3

• 3.8 & 3.9 substitution of Concatenate
• 3.10 does not correctly collect type parameters
• < 3.11.3 wrong substitution behavior; type parameter not removed

from typing import Generic, TypeVar
from typing_extensions import ParamSpec, Concatenate
P = ParamSpec('P')
T = TypeVar("T")

class CLS(Generic[P]): ...

Y = CLS[T] # or with a ParamSpec
# 3.10
Y[str]  # raises TypeError is not a generic class

# 3.8 & 3.9
G9 = CLS[Concatenate[T, P]]
H9 = G9[int, [T]] # should be ok; but TypeError
H9[str]  # should also work

# 3.11.0
G8 = CLS[Concatenate[T, ...]]
H1 = G8[int]
H1[str]  # for python 3.11.0-3 this still has a parameter and does not raise a TypeError

This is a variant of #126 but with generics which require different fixes. There are multiple flavors of this issue depending on the version parameters are not recognized or not substituted correctly.

For a more comprehensive list check the skipped tests of #491 here

---

It's possible that some substitutions with Concatenate worked prior to #479 and caused a regression here, but I am not yet certain.

---

Fixes come with

• Fix Concatenate and Generic with ParamSpec substitution #489

[jeertmans]

Not sure if this is directly related, but Python 3.11 added support for ellipsis ... as last parameter in Concatenate. In Python 3.10, this was not possible (only ParamSpec was allowed).

It seems that typing_extensions provides a 3.10-compatible version of Concatenate when Python < 3.11, which means I cannot use Concatenate[Foo, ...] unless my library's minimal supported Python version is 3.11.

In other words, I was planning to do that:

if sys.version_info >= (3, 11):
    from typing import Concatenate
else:
    from typing_extension import Concatenate

Bar = Concatenate[Foo, ...]

but this doesn't work

[Daraan]

Not sure if this is directly related, but Python 3.11 added support for ellipsis ... as last parameter in Concatenate. In Python 3.10, this was not possible (only ParamSpec was allowed).

The issue in question for this problem is #110 to address this problem for 3.10. A few weeks ago we added #481 to main which solves this problem, but note that there is no release yet.

[jeertmans]

Oh, thanks for pointing to the correct issue :-)

Not sure if this is directly related, but Python 3.11 added support for ellipsis ... as last parameter in Concatenate. In Python 3.10, this was not possible (only ParamSpec was allowed).

The issue in question for this problem is #110 to address this problem for 3.10. A few weeks ago we added #481 to main which solves this problem, but note that there is no release yet.