traverseForVisitor.php

<?php

private function traverseForVisitor(Twig_NodeVisitorInterface $visitor, Twig_Node $node)
{
    $node = $visitor->enterNode($node, $this->env);

    $level = 0;
    /** @var Twig_Node[] $parents */
    $parents = [$node];
    $iterator = $node->getIterator();
    /** @var ArrayIterator[] $stack */
    $stack = [$iterator];

    while_true:
    if ($iterator->valid()) {
        $current = $visitor->enterNode($iterator->current(), $this->env);
        $level++;
        $parents[$level] = $current;
        $stack[$level] = $iterator = $current->getIterator();

        goto while_true;
    } elseif ($level > 0) {
        $level--;
        $iterator = $stack[$level];
        if (false !== $current = $visitor->leaveNode($iterator->current(), $this->env)) {
            $parents[$level]->setNode($iterator->key(), $current);
        } else {
            $parents[$level]->removeNode($iterator->key());
        }
        $iterator->next();

        goto while_true;
    }
    return $visitor->leaveNode($node, $this->env);
}