private function loadDrush(FileLoader $loader, ContainerBuilder $container, array $config)
    {
        if (isset($config['drush'])) {
            $loader->load('drivers/drush.yml');
            if (!isset($config['drush']['alias']) && !isset($config['drush']['root'])) {
                throw new \RuntimeException('Drush `alias` or `root` path is required for the Drush driver.');
            }
            $config['drush']['alias'] = isset($config['drush']['alias']) ? $config['drush']['alias'] : false;
            $container->setParameter('drupal.driver.drush.alias', $config['drush']['alias']);

            $config['drush']['binary'] = isset($config['drush']['binary']) ? $config['drush']['binary'] : 'drush';
            $container->setParameter('drupal.driver.drush.binary', $config['drush']['binary']);

            $config['drush']['root'] = isset($config['drush']['root']) ? $config['drush']['root'] : false;
            $container->setParameter('drupal.driver.drush.root', $config['drush']['root']);

            // Set global arguments.
            $this->setDrushOptions($container, $config);
        }
    }