Issue #3366685: Allow callbacks located in *.update_worker.php to be...

Issue #3366685: Allow callbacks located in *.update_worker.php to be discoverable in the context of queue worker

Closes #3366685

src/Plugin/QueueWorker/UpdateWorker.php

@@ -2,7 +2,9 @@
 
 namespace Drupal\update_worker\Plugin\QueueWorker;
 
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\Core\Queue\QueueWorkerBase;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Sends a message with sparkpost.
@@ -13,14 +15,35 @@ use Drupal\Core\Queue\QueueWorkerBase;
  *   cron = {}
  * )
  */
-class UpdateWorker extends QueueWorkerBase {
+class UpdateWorker extends QueueWorkerBase implements ContainerFactoryPluginInterface {
 
   const QUEUE_NAME = 'update_worker';
 
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    $plugin = new static($configuration, $plugin_id, $plugin_definition);
+    $plugin->moduleHandler = $container->get('module_handler');
+    return $plugin;
+  }
+
   /**
    * {@inheritdoc}
    */
   public function processItem($data) {
+    // Load all files with update_worker.php in the name. This is a recommended
+    // location for update worker callbacks to live. The file won't be
+    // autoaded, so it won't affect site's performance until the queue is
+    // executed.
+    $this->moduleHandler->loadAllIncludes('update_worker.php');
     $callback = $data['callback'];
     $arguments = $data['arguments'];
     if (is_callable($callback)) {