menu_link_highlight-8.x-1.x-dev/menu_link_highlight.module

<?php

use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_BASE_FORM_ID_alter().
 */
function menu_link_highlight_form_menu_link_content_form_alter(array &$form, FormStateInterface $form_state, $form_id) {
  $account = \Drupal::currentUser();

  if (!$account->hasPermission('highlight menu links')) {
    return;
  }

  $menu_link = $form_state->getFormObject()->getEntity();
  $menu_link_options = $menu_link->link ? $menu_link->link->first()->options : [];

  $form['options']['highlight'] = [
    '#type' => 'checkbox',
    '#title' => t('Highlight'),
    '#default_value' => isset($menu_link_options['highlight']) ? $menu_link_options['highlight'] : FALSE,
  ];

  $form['actions']['submit']['#submit'][] = 'menu_link_highlight_menu_link_content_form_submit';
}

/**
 * Submit function for menu add / edit form.
 */
function menu_link_highlight_menu_link_content_form_submit($form, FormStateInterface $form_state) {
  /** @var \Drupal\menu_link_content\Form\MenuLinkContentForm $form_object */
  $form_object = $form_state->getFormObject();
  $menu_link = $form_object->getEntity();

  if (!$menu_link->link) {
    return;
  }

  $menu_link_options = $menu_link->link->first()->options ?: [];
  $highlight = $form_state->getValue('highlight');

  if (isset($highlight) && $highlight == TRUE) {
    $menu_link_options['highlight'] = TRUE;
  }

  $menu_link->link->first()->options = $menu_link_options;
  $menu_link->save();
}

/**
 * Implements template_preprocess_menu().
 */
function menu_link_highlight_preprocess_menu(&$variables) {

  foreach ($variables['items'] as $item) {
    /** @var \Drupal\Core\Menu\MenuLinkDefault $menu_link */

    $menu_link = $item['original_link'];
    $options = $menu_link->getOptions();

    if (isset($options['highlight']) && $options['highlight'] == TRUE) {
      $item['attributes']->setAttribute('class', 'ml-highlight');
    }
  }
}