class Overview

class Overview extends OverviewTerms {

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'forum_overview';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state, VocabularyInterface $taxonomy_vocabulary = NULL) {
    $forum_config = $this
      ->config('forum.settings');
    $vid = $forum_config
      ->get('vocabulary');
    $vocabulary = $this->entityTypeManager
      ->getStorage('taxonomy_vocabulary')
      ->load($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'])) {

        /** @var \Drupal\taxonomy\TermInterface $term */
        $term = $form['terms'][$key]['#term'];
        $form['terms'][$key]['term']['#url'] = Url::fromRoute('forum.page', [
          'taxonomy_term' => $term
            ->id(),
        ]);
        if (!empty($term->forum_container->value)) {
          $title = $this
            ->t('edit container');
          $url = Url::fromRoute('entity.taxonomy_term.forum_edit_container_form', [
            'taxonomy_term' => $term
              ->id(),
          ]);
        }
        else {
          $title = $this
            ->t('edit forum');
          $url = Url::fromRoute('entity.taxonomy_term.forum_edit_form', [
            'taxonomy_term' => $term
              ->id(),
          ]);
        }

        // Re-create the operations column and add only the edit link.
        $form['terms'][$key]['operations'] = [
          '#type' => 'operations',
          '#links' => [
            'edit' => [
              'title' => $title,
              'url' => $url,
            ],
          ],
        ];
      }
    }

    // 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>.', [
      ':container' => Url::fromRoute('forum.add_container')
        ->toString(),
      ':forum' => Url::fromRoute('forum.add_forum')
        ->toString(),
    ]);
    return $form;
  }

}