NodeTypeDeleteConfirm::buildForm

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

public function buildForm(array $form, FormStateInterface $form_state) {
  $num_nodes = $this->queryFactory->get('node')
    ->condition('type', $this->entity->id())
    ->count()
    ->execute();
  if ($num_nodes) {
    $caption = '<p>' . $this->formatPlural($num_nodes, '%type is used by 1 piece of content on your site. You can not remove this content type until you have removed all of the %type content.', '%type is used by @count pieces of content on your site. You may not remove %type until you have removed all of the %type content.', array('%type' => $this->entity->label())) . '</p>';
    $form['#title'] = $this->getQuestion();
    $form['description'] = array('#markup' => $caption);
    return $form;
  }

  return parent::buildForm($form, $form_state);
}