gh-118814: Fix the TypeVar constructor when name is passed by keyword

[serhiy-storchaka]

Fix _PyArg_UnpackKeywordsWithVararg for the case when argument for positional-or-keyword parameter is passed by keyword. There was only one such case in the stdlib -- the TypeVar constructor.

• Issue: TypeVar with bad arguments segfault/misbehavior #118814

[picnixz]

I think I also tried that approach but got a segfault with the example I showed. Could you check whether I may have missed something (or did something incorrect?):

vararg_with_many_args

    a: object
    b: object
    c: object
    d: object
    *args: object
    e: bool
    f: bool = False
    g: bool = False

and test:

• Calling ac_tester.vararg_with_many_args(1, 2, 3, 4, e=5)
• Calling ac_tester.vararg_with_many_args(1, 2, 3, 4, e=5, f=6)

[serhiy-storchaka]

Oh, yes. There are several more bugs in Argument Clinic.

[serhiy-storchaka]

But they are only Argument Clinic bugs and not related to this issue.

[miss-islington-app]

Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @serhiy-storchaka, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 540fcc62f5da982b79504221cac01bfab8b73ba1 3.13

[miss-islington-app]

Sorry, @serhiy-storchaka, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 540fcc62f5da982b79504221cac01bfab8b73ba1 3.12

[bedevere-app]

GH-122806 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-122807 is a backport of this pull request to the 3.12 branch.

[erlend-aasland]

Thanks for fixing this!