Handle publication status of entities that have a published flag.

Handle publication status of viable entities.

Closes #3478179

modules/rdf_sync_published/src/EventSubscriber/RdfSyncPublishedSubscriber.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\rdf_sync_published\EventSubscriber;
+
+use Drupal\Core\Entity\EntityPublishedInterface;
+use Drupal\rdf_sync\Event\RdfSyncEvent;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Listens to the event before syncing the entities.
+ */
+class RdfSyncPublishedSubscriber implements EventSubscriberInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    return [
+      RdfSyncEvent::class => 'filterOutUnpublished',
+    ];
+  }
+
+  /**
+   * Filters out unpublished entities.
+   *
+   * @param \Drupal\rdf_sync\Event\RdfSyncEvent $event
+   *   The event object.
+   */
+  public function filterOutUnpublished(RdfSyncEvent $event): void {
+    $entities = $event->getEntities();
+    // Do not filter out entities that do not implement
+    // EntityPublishedInterface as we cannot determine their publication
+    // status and might filter out entities that should be synced.
+    $entities = array_filter($entities, fn ($entity): bool => !$entity instanceof EntityPublishedInterface || $entity->isPublished());
+    $event->setEntities($entities);
+  }
+
+}