use DrupalblockEntityBlock;

/**
 * Implements hook_preprocess_region().
 */
function MYTHEME_preprocess_region(&$variables) {
  if ($variables['region'] == 'one_page') {
    $blocs_menu = array();
    foreach ($variables['elements'] as $key => $values) {
      if (substr($key, 0, 1) == '#') {
        continue;
      }
      $bloc_object = Block::load($key);
      if (is_object($bloc_object)) {
        $bloc_settings = $bloc_object->get('settings');
        if ($bloc_settings['label_display']) {
          $blocs_menu[] = array(
              'id' => $key,
              'label' => $bloc_settings['label'],
          );
        }
      }
    }
    if (count($blocs_menu)) {
      $variables['region_menu'] = $blocs_menu;
    }
  }
}

{%- if region_menu -%}
<nav class="page-nav-anchor">
  <ul>
{%- for menu in region_menu -%}
  <li><a rel="scroll" href="#block-{{ menu['id'] }}">{{ menu['label'] }}</a></li>
{%- endfor -%}
  </ul>
</nav>
{%- endif -%}