class Custom

class Custom extends FieldPluginBase {
  
  /**
   * {@inheritdoc}
   */
  public function usesGroupBy() {
    return FALSE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function query() {
    // do nothing -- to override the parent query.
  }
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    // Override the alter text option to always alter the text.
    $options['alter']['contains']['alter_text'] = [
      'default' => TRUE,
    ];
    $options['hide_alter_empty'] = [
      'default' => FALSE,
    ];
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    parent::buildOptionsForm($form, $form_state);
    // Remove the checkbox
    unset($form['alter']['alter_text']);
    unset($form['alter']['text']['#states']);
    unset($form['alter']['help']['#states']);
    $form['#pre_render'][] = [
      $this,
      'preRenderCustomForm',
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public static function trustedCallbacks() {
    $callbacks = parent::trustedCallbacks();
    $callbacks[] = 'preRenderCustomForm';
    return $callbacks;
  }
  
  /**
   * {@inheritdoc}
   */
  public function render(ResultRow $values) {
    // Return the text, so the code never thinks the value is empty.
    return ViewsRenderPipelineMarkup::create(Xss::filterAdmin($this->options['alter']['text']));
  }
  
  /**
   * Prerender function to move the textarea to the top of a form.
   *
   * @param array $form
   *   The form build array.
   *
   * @return array
   *   The modified form build array.
   */
  public function preRenderCustomForm($form) {
    $form['text'] = $form['alter']['text'];
    $form['help'] = $form['alter']['help'];
    unset($form['alter']['text']);
    unset($form['alter']['help']);
    return $form;
  }

}