parser: Fix 3 corner cases

[drinkcat]

This can wait a bit, e.g. after #7656 and #7675 so they don't have to rebase (I don't think there's any direct logical conflict but maybe some context).

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uucore: parser: num_parser: Parse "0x"/"0b" as PartialMatch

printf treats "0x" as a partial match of 0 and "x".

uucore: parser: num_parser: Ignore empty exponents

Numbers like 123.15e or 123.15e- should return PartialMatch.

Numbers like e, .e are not valid.

Fixes #7685.

uucore: parser: num_parser: Return error if no digit has been parsed

This is mostly important when parsing digits like . and 0x.
where we should return an error.

Fixes #7684.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[drinkcat]

Resolved conflicts.

[sylvestre]

can we have tests in test/by-util/ too ?
thanks
i like having high level integration tests

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[tertsdiepraam]

This seems fine although the Option<BigInt> feels a bit convoluted? I wonder if all this might benefit from not using an iterator but just operating on the slice. I find that to be much easier to reason about usually. I won't mind this being merged though.

[drinkcat]

can we have tests in test/by-util/ too ?

Will do (those end-to-end tests were very useful when doing refactoring...)

This seems fine although the Option<BigInt> feels a bit convoluted?

My first instinct (coming from more "classical" languages) was to carry that information in a boolean (digit_parsed?), and then, digits value would only be considered if digit_parsed is true (and the same for the exponent). But, that's... basically what an Option does?

Happy to hear your suggestions though ,-)

I wonder if all this might benefit from not using an iterator but just operating on the slice. I find that to be much easier to reason about usually. I won't mind this being merged though.

This function badly needs some rethinking/splitting, overall. I can look a bit more into it after this (hopefully we're done with most of the big features/bug fixes work now...)

[drinkcat]

can we have tests in test/by-util/ too ? thanks i like having high level integration tests

Done!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)

[RenjiSann]

Thanks a lot !