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@ 2021-01-16T23:05:34Z

<?php

function is_cyclic(array &$array, int $maxDepth = -1)
{
    if ($maxDepth === 0) {
        throw new Exception('Maximum nesting level exceeded.');
    }
    
    $lastKey = array_key_last($array);
    if ($lastKey === null) {
        // Array is empty
        return false;
    }
    static $marker;
    if ($marker === null) {
        $marker = new stdClass();
    }
    if ($array[$lastKey] === $marker) {
        return true;
    }
    $array[] = $marker;
    foreach ($array as &$item) {
        if (is_array($item) && is_cyclic($item, $maxDepth - 1)) {
            array_pop($array);
            return true;
        }
    }
    array_pop($array);
    return false;
}

function craft_bomb() {
    $array = [1, [2, 3]];
    $array[1][1] = &$array;
    return $array;
}

$bomb = craft_bomb();
var_export(is_cyclic($bomb, 10));

Output for 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.31, 8.2.0 - 8.2.26, 8.3.0 - 8.3.15, 8.4.1 - 8.4.2: Fatal error: Uncaught Exception: Maximum nesting level exceeded. in /in/Nl7PZ:6 Stack trace: #0 /in/Nl7PZ(23): is_cyclic(Array, 0) #1 /in/Nl7PZ(23): is_cyclic(Array, 1) #2 /in/Nl7PZ(23): is_cyclic(Array, 2) #3 /in/Nl7PZ(23): is_cyclic(Array, 3) #4 /in/Nl7PZ(23): is_cyclic(Array, 4) #5 /in/Nl7PZ(23): is_cyclic(Array, 5) #6 /in/Nl7PZ(23): is_cyclic(Array, 6) #7 /in/Nl7PZ(23): is_cyclic(Array, 7) #8 /in/Nl7PZ(23): is_cyclic(Array, 8) #9 /in/Nl7PZ(23): is_cyclic(Array, 9) #10 /in/Nl7PZ(39): is_cyclic(Array, 10) #11 {main} thrown in /in/Nl7PZ on line 6
Process exited with code 255.

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