class InstallerServiceProvider

class InstallerServiceProvider extends NormalInstallerServiceProvider implements ServiceProviderInterface, ServiceModifierInterface {
  
  /**
   * {@inheritdoc}
   */
  public function register(ContainerBuilder $container) {
    // Inject the special configuration storage for the installer.
    // This special implementation MUST NOT be used anywhere else than the early
    // installer environment.
    $container->register('config.storage', 'Drupal\\Core\\Config\\InstallStorage');
    // Replace services with in-memory implementations.
    $container->register('keyvalue', 'Drupal\\Core\\KeyValueStore\\KeyValueMemoryFactory');
    $container->register('keyvalue.expirable', 'Drupal\\Core\\KeyValueStore\\KeyValueNullExpirableFactory');
    // Replace services with no-op implementations.
    $container->register('url_generator', 'Drupal\\Core\\Routing\\NullGenerator')
      ->addArgument(new Reference('request_stack'));
    $container->register('path_processor_manager', 'Drupal\\Core\\PathProcessor\\NullPathProcessorManager');
    $container->register('router.dumper', 'Drupal\\Core\\Routing\\NullMatcherDumper');
    // Replace the route builder with an empty implementation.
    // @todo Convert installer steps into routes; add an installer.routing.yml.
    $definition = $container->getDefinition('router.builder');
    $definition->setClass('Drupal\\Core\\Installer\\InstallerRouteBuilder')
      ->setLazy(FALSE);
    parent::register($container);
  }
  
  /**
   * {@inheritdoc}
   */
  public function alter(ContainerBuilder $container) {
    // Disable Twig cache (php storage does not exist yet).
    $twig_config = $container->getParameter('twig.config');
    $twig_config['cache'] = FALSE;
    $container->setParameter('twig.config', $twig_config);
    // No service may persist when the early installer kernel is rebooted into
    // the production environment.
    // @todo The DrupalKernel reboot performed by drupal_install_system() is
    //   actually not a "regular" reboot (like ModuleInstaller::install()), so
    //   services are not actually persisted.
    foreach ($container->findTaggedServiceIds('persist') as $id => $tags) {
      $definition = $container->getDefinition($id);
      $definition->clearTag('persist');
    }
  }

}