False positive on non existing array offset if array is used as foreach key

[HonzaMatosik]

Bug report

If array is used as foreach key, phpstan reports $context["_key"] as non existing offset, but it is defined (tested on PHP 8.1).

Also related: Offset can exist (if $context["value"] is not empty) outside of forech scope, so calling unset should be safe.

Code snippet that reproduces the problem

<?php declare(strict_types = 1);

$context = [
    'values' => [1, 2, 3],
];
foreach ($context['values'] as $context["_key"] => $context["value"]) {
    echo sprintf("Key: %s, Value: %s\n", $context["_key"], $context["value"]);
}

unset($context["_key"]);

https://phpstan.org/r/6a63cb67-ecf7-484b-87b3-283595ddd3ef

Expected output

No errors

Did PHPStan help you today?

Yes! It makes my code safer and more reliable every day since 2016.

[staabm]

Oh wow. Never considerd writing code like that. feels too magic for my feelings.

Is this just a theoretical problem, or do you really have it like that?

if you write explicitly what you want todo it works like expected https://phpstan.org/r/276f7192-826b-431b-97bc-bf3babbe8e24

[herndlm]

TIL: loops can assign array offsets :O

update: look at that, while we're surprised by the magic here, @rvanvelzen is already fixing it. impressive! ;)

[HonzaMatosik]

@staabm

Oh wow. Never considerd writing code like that. feels too magic for my feelings.

I totally agree. 😅

Is this just a theoretical problem, or do you really have it like that?

It's more of a practical problem, but it isn't blocking as multiple workarounds works. Specifically I'm writing phpstan extension for Twig, and this is basically how Twig foreach loop looks after compilation.

[github-actions]

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.