CommentTypeDeleteForm::buildForm

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

public function buildForm(array $form, FormStateInterface $form_state) {
  $comments = $this->queryFactory->get('comment')->condition('comment_type', $this->entity->id())->execute();
  $entity_type = $this->entity->getTargetEntityTypeId();
  $caption = '';
  foreach (array_keys($this->commentManager->getFields($entity_type)) as $field_name) {
    /** @var \Drupal\field\FieldStorageConfigInterface $field_storage */
    if (($field_storage = FieldStorageConfig::loadByName($entity_type, $field_name)) && $field_storage->getSetting('comment_type') == $this->entity->id() && !$field_storage->isDeleted()) {
      $caption .= '<p>' . $this->t('%label is used by the %field field on your site. You can not remove this comment type until you have removed the field.', array(
        '%label' => $this->entity->label(),
        '%field' => $field_storage->label(),
      )) . '</p>';
    }
  }

  if (!empty($comments)) {
    $caption .= '<p>' . $this->formatPlural(count($comments), '%label is used by 1 comment on your site. You can not remove this comment type until you have removed all of the %label comments.', '%label is used by @count comments on your site. You may not remove %label until you have removed all of the %label comments.', array('%label' => $this->entity->label())) . '</p>';
  }
  if ($caption) {
    $form['description'] = array('#markup' => $caption);
    return $form;
  }
  else {
    return parent::buildForm($form, $form_state);
  }
}