gh-87106: Fix inspect.signature.bind handling of positional-only arguments with **kwargs

[jacobtylerwalls]

gh-87106
Closes#87106

If a function signature has a variadic keyword argument (like **kwargs), then providing a keyword with the same name as a positional-only argument will still succeed, and become available on kwargs.

Before
inspect.signature(f).bind(pos_only='val') might either:

• raise TypeError unnecessarily if the positional-only arg had a default
• raise TypeError with a different flavor of error message than runtime (runtime mentions the missing positional arg, but bind() mentioned the name collision, which wasn't the problem)

Now
These are fixed.

Prior related work
#16800

[sobolevn]

Thanks!

[jacobtylerwalls]

👋 @sobolevn would you be interested to take another look?

[sobolevn]

I agree with the fix in general. However, there are still some things to polish and improve :)

Thanks a lot for your work!

[jacobtylerwalls]

Thanks for your suggestions, @sobolevn. Should I move some of the new cases to test_signature_bind_posonly_kwargs()?

[sobolevn]

@serhiy-storchaka do you have any additional feedback?

[serhiy-storchaka]

LGTM.

[miss-islington-app]

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

[miss-islington-app]

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

[bedevere-app]

GH-118984 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-118985 is a backport of this pull request to the 3.13 branch.