number_format() Support rounding negative places

[marc-mabe]

This PR adds support for rounding negative $decimals in number_format().

Previously negative $decimals got silently ignored and the number got rounded to zero decimal places.
With this change, when $decimals is negative, $num is rounded to $decimals significant digits before the decimal point.

This is matching the behavior for the $precision argument of round().

The previous behavior wasn't documented or tested at all.

[jorgsowa]

Hey @marc-mab

Nice change! I am not sure what's the exact process of merging code, but shouldn't this improvement be documented in changelog somehow? It's for sure BC breaking change.

[marc-mabe]

Hi @jorgsowa, yes, it should be documented somehow but I'm not sure either about the process. Was hoping to get some reviews first and then what needs to be done for documenting it.

About BC break I think this is extremely low and as the previous behavior wasn't documented or tested I would classify that into undefined behavior.

I hope this little change doesn't need an RFC.

[iluuu1994]

It makes sense to match the behavior with round. You can send a mail to the internals mailing list and ask for feedback. Generally, there's an unwritten rule that without objection after a couple of weeks, a small behavioral change is acceptable. Just make sure to explicitly mention that. E.g. if there are no objections, Ilija has agreed to merge this for master. We will of course document this accordingly.

[bukka]

I don't have an objection against this change. Just test needs improving.

[marc-mabe]

@bukka Thanks for your review ... I have reverted the modified test file and added a new one testing multiple cases on the $decimals param.

[marc-mabe]

@bukka @iluuu1994 The two failing tests seems to be very much unrelated to this change. As I don't have the permissions to restart tests should I commit a dummy change or how is the way forward?

[iluuu1994]

@marc-mabe No worries, CI doesn't need to be green if it's obviously unrelated.

how is the way forward?

There hasn't been any feedback so I think we can merge this change for PHP 8.3. I'll do so in the coming days.

[bukka]

I meged it so #11584 can get rebased and reviewed in time.