FormErrorHandler::displayErrorMessages

protected FormErrorHandler::displayErrorMessages(array $form, FormStateInterface $form_state)

protected function displayErrorMessages(array $form, FormStateInterface $form_state) {
  $error_links = [];
  $errors = $form_state->getErrors();
  // Loop through all form errors and check if we need to display a link.
  foreach ($errors as $name => $error) {
    $form_element = FormElementHelper::getElementByName($name, $form);
    $title = FormElementHelper::getElementTitle($form_element);

    // Only show links to erroneous elements that are visible.
    $is_visible_element = Element::isVisibleElement($form_element);
    // Only show links for elements that have a title themselves or have
    // children with a title.
    $has_title = !empty($title);
    // Only show links for elements with an ID.
    $has_id = !empty($form_element['#id']);

    // Do not show links to elements with suppressed messages. Most often
    // their parent element is used for inline errors.
    if (!empty($form_element['#error_no_message'])) {
      unset($errors[$name]);
    }
    elseif ($is_visible_element && $has_title && $has_id) {
      $error_links[] = $this->l($title, Url::fromRoute('<none>', [], ['fragment' => $form_element['#id'], 'external' => TRUE]));
      unset($errors[$name]);
    }
  }

  // Set normal error messages for all remaining errors.
  foreach ($errors as $error) {
    $this->drupalSetMessage($error, 'error');
  }

  if (!empty($error_links)) {
    $render_array = [
      [
        '#markup' => $this->formatPlural(count($error_links), '1 error has been found: ', '@count errors have been found: '),
      ],
      [
        '#theme' => 'item_list',
        '#items' => $error_links,
        '#context' => ['list_style' => 'comma-list'],
      ],
    ];
    $message = $this->renderer->renderPlain($render_array);
    $this->drupalSetMessage($message, 'error');
  }
}