Overview::buildForm

public Overview::buildForm(array $form, FormStateInterface $form_state)

public function buildForm(array $form, FormStateInterface $form_state) {
  $forum_config = $this->config('forum.settings');
  $vid = $forum_config->get('vocabulary');
  $vocabulary = $this->entityManager->getStorage('taxonomy_vocabulary')->load($vid);
  if (!$vocabulary) {
    throw new NotFoundHttpException();
  }

  // Build base taxonomy term overview.
  $form = parent::buildForm($form, $form_state, $vocabulary);

  foreach (Element::children($form['terms']) as $key) {
    if (isset($form['terms'][$key]['#term'])) {
      $term = $form['terms'][$key]['#term'];
      $form['terms'][$key]['term']['#url'] = Url::fromRoute('forum.page', ['taxonomy_term' => $term->id()]);
      unset($form['terms'][$key]['operations']['#links']['delete']);
      $route_parameters = $form['terms'][$key]['operations']['#links']['edit']['url']->getRouteParameters();
      if (!empty($term->forum_container->value)) {
        $form['terms'][$key]['operations']['#links']['edit']['title'] = $this->t('edit container');
        $form['terms'][$key]['operations']['#links']['edit']['url'] = Url::fromRoute('entity.taxonomy_term.forum_edit_container_form', $route_parameters);
      }
      else {
        $form['terms'][$key]['operations']['#links']['edit']['title'] = $this->t('edit forum');
        $form['terms'][$key]['operations']['#links']['edit']['url'] = Url::fromRoute('entity.taxonomy_term.forum_edit_form', $route_parameters);
      }
      // We don't want the redirect from the link so we can redirect the
      // delete action.
      unset($form['terms'][$key]['operations']['#links']['edit']['query']['destination']);
    }
  }

  // Remove the alphabetical reset.
  unset($form['actions']['reset_alphabetical']);

  // Use the existing taxonomy overview submit handler.
  $form['terms']['#empty'] = $this->t('No containers or forums available. <a href=":container">Add container</a> or <a href=":forum">Add forum</a>.', array(
    ':container' => $this->url('forum.add_container'),
    ':forum' => $this->url('forum.add_forum')
  ));
  return $form;
}