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Keep optional groups optional within a matched regex alternation branch - #6596
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When building the tagged union for a single top-level alternation, the groups of the matched branch were forced non-optional, which also dropped their own optional quantifiers, e.g. `(?:-(?P<bar>\d+))?`. Such a group is now only forced out of the alternation's optionality. With PREG_UNMATCHED_AS_NULL on PHP 7.2 and 7.3, an unmatched group followed by a matched one is reported as null, not as an empty string. Only the trailing unmatched groups are omitted there. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01KjXHtRyzsYF9xktijyaRBr
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Closes phpstan/phpstan#15297
The reported errors show up when the analysed PHP version is below 7.4 (e.g. PHP 7.2/7.3 on the playground). Two inaccuracies in
RegexArrayShapeMatchercaused them:forceNonOptional()-ed, which also dropped its own optional quantifier, e.g.(?:-(?P<bar1>[0-9]+))?. PHP omits such a trailing unmatched group (withoutPREG_UNMATCHED_AS_NULL, or on 7.2/7.3), but PHPStan inferredbar1: numeric-stringas always present. The matched branch's groups are now only forced out of the alternation's optionality: they remain optional when they, or a parent within the same branch, are optionally quantified.PREG_UNMATCHED_AS_NULLon PHP 7.2 and 7.3 was modelled as no flag at all, i.e.''for unmatched groups. Those versions already report an unmatched group followed by a matched one asnull; only trailing unmatched groups are omitted. Verified against php:7.2-cli and php:7.3-cli.On PHP 7.3 the reproducer now reports one remaining error which is a true positive: when
foo1isnullthe second branch matched, so$matches["foo2"]always exists and?? ""is dead. PHP 7.4+ was and remains error-free.Tests:
nsrt/bug-15297.php– flag-less shapes (also(?:(a))?(b)|(c), previously inferred as always'a')Bug15297Php73Test– PHP 7.3 shapes withPREG_UNMATCHED_AS_NULLNullCoalesceRulePhp73Test– the playground reproducer verbatim on PHP 7.3🤖 Generated with Claude Code
https://claude.ai/code/session_01KjXHtRyzsYF9xktijyaRBr