add PREG_UNMATCHED_AS_NULL flag to allow distinguish between unmatched subpatterns and empty matches

[nicolas-grekas]

Makes #1303 opt-in, fixing the BC break it introduced.

[Majkl578]

👍 But the name sounds strange - I originally suggested something like PREG_SUBPATTERN_UNMATCHED_NULL or PREG_UNMATCHED_AS_NULL, how about that?

[sgolemon]

Agree with @Majkl578 on name, and I like PREG_UNMATCHED_AS_NULL (but I don't care enough to bikeshed on it)

I see you've updated (essentially reverted from prior commit) the tests dealing with unmatched subpatterns, but would you mind adding a test which uses the constant?

[Fleshgrinder]

I second PREG_UNMATCHED_AS_NULL and think its very important to get the naming right (always).

[nicolas-grekas]

Updated
Tests with the const already exist, see bug61780*.phpt

[sgolemon]

Oh, weird, dunno how I missed the tests before. Anyway, thumbs up from me.

[nicolas-grekas]

Could this be merged please? That'd help us try 7.2 as it removes the BC break. Then if the new part needs improvement, it'll be open to another PR.

[remicollet]

LGTM, will merge it asap

[php-pulls]

Comment on behalf of remi at php.net:

Merged, thanks

[nicolas-grekas]

ping @cmb69 FYI since you wanted to have another behavior when the flag (another one) is passed.
Thanks @remicollet for merging.

[cmb69]

@nicolas-grekas Thanks for the ping. Since others like this PR, it's okay for me to have this behavior. :)