ForumNodeBreadcrumbBuilder.php

<?php

namespace Drupal\forum\Breadcrumb;

use Drupal\Core\Link;
use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Breadcrumb builder for forum nodes.
 */
class ForumNodeBreadcrumbBuilder extends ForumBreadcrumbBuilderBase {
  
  /**
   * {@inheritdoc}
   */
  public function applies(RouteMatchInterface $route_match) {
    return $route_match->getRouteName() == 'entity.node.canonical' && $route_match->getParameter('node') && $this->forumManager
      ->checkNodeType($route_match->getParameter('node'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function build(RouteMatchInterface $route_match) {
    $breadcrumb = parent::build($route_match);
    $breadcrumb->addCacheContexts([
      'route',
    ]);
    $parents = $this->termStorage
      ->loadAllParents($route_match->getParameter('node')->forum_tid);
    if ($parents) {
      $parents = array_reverse($parents);
      foreach ($parents as $parent) {
        $breadcrumb->addCacheableDependency($parent);
        $breadcrumb->addLink(Link::createFromRoute($parent->label(), 'forum.page', [
          'taxonomy_term' => $parent->id(),
        ]));
      }
    }
    return $breadcrumb;
  }

}