class MenuLinkEditForm

class MenuLinkEditForm extends FormBase {
  
  /**
   * The class resolver.
   *
   * @var \Drupal\Core\DependencyInjection\ClassResolverInterface
   */
  protected $classResolver;
  
  /**
   * Constructs a MenuLinkEditForm object.
   *
   * @param \Drupal\Core\DependencyInjection\ClassResolverInterface $class_resolver
   *   The class resolver.
   */
  public function __construct(ClassResolverInterface $class_resolver) {
    $this->classResolver = $class_resolver;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('class_resolver'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'menu_link_edit';
  }
  
  /**
   * {@inheritdoc}
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param \Drupal\Core\Menu\MenuLinkInterface $menu_link_plugin
   *   The plugin instance to use for this form.
   */
  public function buildForm(array $form, FormStateInterface $form_state, MenuLinkInterface $menu_link_plugin = NULL) {
    $form['menu_link_id'] = [
      '#type' => 'value',
      '#value' => $menu_link_plugin->getPluginId(),
    ];
    $class_name = $menu_link_plugin->getFormClass();
    $form['#plugin_form'] = $this->classResolver
      ->getInstanceFromDefinition($class_name);
    $form['#plugin_form']->setMenuLinkInstance($menu_link_plugin);
    $form += $form['#plugin_form']->buildConfigurationForm($form, $form_state);
    $form['actions'] = [
      '#type' => 'actions',
    ];
    $form['actions']['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Save'),
      '#button_type' => 'primary',
    ];
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    $form['#plugin_form']->validateConfigurationForm($form, $form_state);
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $link = $form['#plugin_form']->submitConfigurationForm($form, $form_state);
    $this->messenger()
      ->addStatus($this->t('The menu link has been saved.'));
    $form_state->setRedirect('entity.menu.edit_form', [
      'menu' => $link->getMenuName(),
    ]);
  }

}