StackedSessionHandlerPass.php

<?php

namespace Drupal\Core\DependencyInjection\Compiler;

use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Reference;

/**
 * Provides a compiler pass for stacked session save handlers.
 */
class StackedSessionHandlerPass implements CompilerPassInterface {
    
    /**
     * {@inheritdoc}
     */
    public function process(ContainerBuilder $container) {
        if ($container->hasDefinition('session_handler')) {
            return;
        }
        $session_handler_proxies = [];
        $priorities = [];
        foreach ($container->findTaggedServiceIds('session_handler_proxy') as $id => $attributes) {
            $priorities[$id] = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
            $session_handler_proxies[$id] = $container->getDefinition($id);
        }
        array_multisort($priorities, SORT_ASC, $session_handler_proxies);
        $decorated_id = 'session_handler.storage';
        foreach ($session_handler_proxies as $id => $decorator) {
            // Prepend the inner session handler as first constructor argument.
            $arguments = $decorator->getArguments();
            array_unshift($arguments, new Reference($decorated_id));
            $decorator->setArguments($arguments);
            $decorated_id = $id;
        }
        $container->setAlias('session_handler', $decorated_id);
    }

}