preg_match param-out is a list, and phpstan kind of agrees, but not enough

Bug report

The $match param-out in preg_match($pattern, $string, $match) is always a list (unless named capture groups). Phpstan kind of knows that:

Dumped type: array{0?: string, 1?: non-falsy-string, 2?: numeric-string}

But that's not exactly a list, so it complains when I return that when a list<string> is expected.

I think it's impossible to get a $match where 0 and 2 are set, but 1 is not. And other non-list combinations. PregMatchParameterOutTypeExtension and RegexArrayShapeMatcher should know that.

Code snippet that reproduces the problem

https://phpstan.org/r/5efc781a-6381-4d1b-ac96-cd96f373ece4

Expected output

This exact example is fine, because Phpstan doesn't complain about the return value, but without the if breakout, it does complain, and that's wrong IMO. Even without knowing the preg_match return value, we know that $match is a list.

Unless I am mistaken, and it IS possible to get a non-list array. But I don't think so. See Playground example too. Without the breakout if, Phpstan complains, even though an empty array is a perfectly valid list<string>. And after the if $match is a known list?? something is off here.

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@staabm

/cc @staabm Is this true? If yes you can set the ConstantArrayType isList constructor argument. Also you can check what list{...} resolves to in TypeNodeResolver. It might be that, or it might be intersection with AccessoryArrayListType.

I need to double check. It at least depends on $flags I guess

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This wasn't actually fixed, it's exposed after phpstan/phpstan-src#4399 again

@rudiedirkx

@rudiedirkx After the latest push in 2.2.x, PHPStan now reports different result with your code snippet:

@@ @@
- 8: Dumped type: array{0?: string, 1?: non-falsy-string, 2?: numeric-string}
-10: Dumped type: array{string, non-falsy-string, numeric-string}
+ 8: Dumped type: list{0?: string, 1?: non-falsy-string, 2?: numeric-string}
+10: Dumped type: array{non-falsy-string, non-falsy-string, numeric-string}

Full report

Line	Error
8	`Dumped type: list{0?: string, 1?: non-falsy-string, 2?: numeric-string}`
10	`Dumped type: array{non-falsy-string, non-falsy-string, numeric-string}`

Closed via merging phpstan/phpstan-src#5209

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.

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preg_match param-out is a list, and phpstan kind of agrees, but not enough #12397

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preg_match param-out is a list, and phpstan kind of agrees, but not enough #12397

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Did PHPStan help you today? Did it make you happy in any way?

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ondrejmirtes commented on Jan 8, 2025

staabm commented on Jan 8, 2025

github-actions commented on Apr 25, 2025

ondrejmirtes commented on Feb 27, 2026

phpstan-bot commented on Feb 27, 2026

phpstan-bot commented on Mar 12, 2026

github-actions commented on Apr 13, 2026

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