GeezerVison

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@encukou

The current code covers all combinations of plain_names & names_with_default being NULL and non-NULL. Removing one of the cases breaks that, leaving no hint about why this would fall through to the empty posargs case.
If it was me, I'd replace the branch with something like:

// With the current grammar, we never get here.
// When that changes, remove the assert, and test thoroughly.
assert(0);
*posargs = plain_names;

I'd replace the branch with something like:

I agree, that's better. Should I resubmit?

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This looks good to me, thanks!
I see you've marked it as draft, do you still want to make changes?

Thanks! I meant to wrap this up over the weekend, but forgot. I will do it this week.

@encukou I split the changes into two commits, one to improve coverage and the other to reorganize the if-else structure.

Thanks!

For the future: please avoid force-pushing to CPython -- when reviewed commits disappear, the review needs to be restarted. (In this commit it's not a problem, as it's just a few lines.)
Reorganizing the commits doesn't help, since all PRs are squashed when merging.

Thanks again for your help and guidance through the whole process.