trait PluginFormTrait in Search API 8

trait PluginFormTrait {

  /**
   * Form validation handler.
   *
   * @param array $form
   *   An associative array containing the structure of the plugin form as built
   *   by static::buildConfigurationForm().
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the complete form.
   *
   * @see \Drupal\Core\Plugin\PluginFormInterface::validateConfigurationForm()
   */
  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
  }

  /**
   * Form submission handler.
   *
   * @param array $form
   *   An associative array containing the structure of the plugin form as built
   *   by static::buildConfigurationForm().
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the complete form.
   *
   * @see \Drupal\Core\Plugin\PluginFormInterface::submitConfigurationForm()
   */
  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {

    // @todo Clean this up once we depend on Drupal 9.0+.
    if ($this instanceof ConfigurableInterface || $this instanceof DrupalConfigurablePluginInterface) {
      $this
        ->setConfiguration($form_state
        ->getValues());
    }
  }

}