[php-src] Issue #11397: PCRE: Unmatched capture groups result inconsistency

Issue: https://github.com/php/php-src/issues/11397 Author: mvorisek ### Description Currently, unmatched capture groups are added to the result when they are before matched capture group, but are not added when they are after (ie. unmatched capture group is not followed by any other matched capture group). <br> The docs about "PREG_UNMATCHED_AS_NULL" flag says: > If this flag is passed, unmatched subpatterns are reported as null; otherwise they are reported > as an empty string. So **all** capture groups, even the unmatched at the end, should be always present. <br> The following code: ```php <?php preg_match('/(?<foo>y)?x(?<bar>y)?/', 'x', $matches); print_r($matches); preg_match('/(?<foo>y)?()x(?<bar>y)?/', 'x', $matches); // notice extra "()" print_r($matches); ``` Resulted in this output: ``` Array ( [0] => x ) Array ( [0] => x [foo] => [1] => [2] => ) ``` But I expected this output instead: ``` Array ( [0] => x [foo] => [1] => [2] => [bar] => [3] => ) Array ( [0] => x [foo] => [1] => [2] => [bar] => [3] => ) ``` online repro: https://3v4l.org/ra13Q