class Broken

class Broken extends PluginBase implements BlockPluginInterface, ContainerFactoryPluginInterface {
  use BlockPluginTrait;
  use CacheableDependencyTrait;
  
  /**
   * The current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $currentUser;
  
  /**
   * Creates a Broken Block instance.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   The current user.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, AccountInterface $current_user) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->currentUser = $current_user;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('current_user'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function build() {
    $build = [];
    if ($this->currentUser
      ->hasPermission('administer blocks')) {
      $build += $this->brokenMessage();
    }
    return $build;
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    return $this->brokenMessage();
  }
  
  /**
   * Generate message with debugging information as to why the block is broken.
   *
   * @return array
   *   Render array containing debug information.
   */
  protected function brokenMessage() {
    $build['message'] = [
      '#markup' => $this->t('This block is broken or missing. You may be missing content or you might need to enable the original module.'),
    ];
    return $build;
  }

}