The method \TYPO3\CMS\Core\Utility\ArrayUtility::filterRecursive declares its $callback argument as of type callable, but uses it as a \Closure via $callback(...).

Current State¶

public static function filterRecursive(array $array, callable $callback = null): array
// ... 
    foreach ($array as $key => $value) {
// ...
        if (!$callback($value)) { // <--- used as a \Closure, but declared as a callable
            unset($array[$key]);
        }
    }
// ...
}

• $callback argument declaration in line 848
• $callback argument usage in line 859

Possible Strategies¶

We could ...

1. either change the filterRecursive-methods signature to ..., \Closure $callback..., or ...
2. we fix the use of the $callback argument in the method-body.

I decided to go for the latter (2.) and fix the use of the $callback argument in the method-body, as it seems to be quite common in the core to use callable type, instead of \Closure. The fixed line will then contain a call_user_func($callback, $value)-function call.

Proposed Solution¶

public static function filterRecursive(array $array, callable $callback = null): array
// ... 
    foreach ($array as $key => $value) {
// ...
        if (!call_user_func($callback, $value)) { // <--- now used and declared as a callable
            unset($array[$key]);
        }
    }
// ...
}

Conclusion¶

Fixing the use of $callback in the static \TYPO3\CMS\Core\Utility\ArrayUtility::filterRecursive method, won't harm existing installations. Adding an appropriate unit-test ensures the correct behaviour.

Therefore I'll create a PR to fix this issue with the proposed solution and I'll add an appropriate test to \TYPO3\CMS\Core\Tests\Unit\Utility\ArrayUtilityTest too.

A quick search over the core-sources did not reveal any other misuses of callable-types as closure. But do not bet on me, as I just took 5 minutes to identify potential candidates.