class ShortcutForm

class ShortcutForm extends ContentEntityForm {
  
  /**
   * The entity being used by this form.
   *
   * @var \Drupal\shortcut\ShortcutInterface
   */
  protected $entity;
  
  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {
    $form = parent::form($form, $form_state);
    $form['#attached']['library'][] = 'core/drupal.form';
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function save(array $form, FormStateInterface $form_state) {
    $entity = $this->entity;
    $status = $entity->save();
    $url = $entity->getUrl();
    // There's an edge case where a user can have permission to
    // 'link to any content', but has no right to access the linked page. So we
    // check the access before showing the link.
    if ($url->access()) {
      $view_link = Link::fromTextAndUrl($entity->getTitle(), $url)
        ->toString();
    }
    else {
      $view_link = $entity->getTitle();
    }
    if ($status == SAVED_UPDATED) {
      $message = $this->t('The shortcut %link has been updated.', [
        '%link' => $view_link,
      ]);
    }
    else {
      $message = $this->t('Added a shortcut for %title.', [
        '%title' => $view_link,
      ]);
    }
    $this->messenger()
      ->addStatus($message);
    $form_state->setRedirect('entity.shortcut_set.customize_form', [
      'shortcut_set' => $entity->bundle(),
    ]);
  }

}