3200888: set 'is previewing' on entity edit form routes

Closes #3200888

src/Plugin/PreviewDetector/RenderedEntityPreviewDetector.php

@@ -6,6 +6,7 @@ use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityPublishedInterface;
 use Drupal\entity_reference_preview\PreviewDetectorPluginBase;
 use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\Routing\Route;
 
 /**
  * Plugin implementation of the preview_detector.
@@ -26,8 +27,9 @@ class RenderedEntityPreviewDetector extends PreviewDetectorPluginBase {
     if (!$entity) {
       return FALSE;
     }
-    // This should be the same logic used to show or hide the entity tab Latest.
-    return $this->entityIsPreviewing($entity);
+    $route = $request->attributes->get('_route_object');
+    return $this->routeIsPreviewing($route, $entity->getEntityTypeId()) ||
+      $this->entityIsPreviewing($entity);
   }
 
   /**
@@ -55,6 +57,22 @@ class RenderedEntityPreviewDetector extends PreviewDetectorPluginBase {
     return reset($publishable_entity_params);
   }
 
+  /**
+   * Checks the route for "load latest revision" parameter flag.
+   *
+   * @param \Symfony\Component\Routing\Route $route
+   *   The route for the current request.
+   * @param string $entity_type_id
+   *   The ID of entity type for the route parameter.
+   *
+   * @return bool
+   *   TRUE if the route is for a preview.
+   */
+  private function routeIsPreviewing(Route $route, string $entity_type_id): bool {
+    $route_params = $route->getOption('parameters');
+    return $route_params[$entity_type_id]['load_latest_revision'] ?? FALSE;
+  }
+
   /**
    * The entity preview function.
    *