Break circular dependencies in EntityReferenceRevisionsFieldItemList::hasAffectingChanges()

We found an issue with EntityReferenceRevisionsFieldItemList::hasAffectingChanges()

We have a structur like this:

Node A -> Paragraph -> Node B -> Paragraph -> Node C -> Paragraph -> Node B

As you can see there is a circular dependency between Node B and Node C. So when we try to save Node A we get stuck in a infinite loop due to hasAffectingChanges() calling hasTranslationChanges() which in return calls hasAffectingChanges().

Closes #3039442

src/EntityReferenceRevisionsFieldItemList.php

@@ -15,6 +15,12 @@ use Drupal\Core\Field\EntityReferenceFieldItemListInterface;
  */
 class EntityReferenceRevisionsFieldItemList extends EntityReferenceFieldItemList implements EntityReferenceFieldItemListInterface {
 
+  /**
+   * Static cache that remembers if an entity has affecting changes or not.
+   * This is needed to break a circular dependencies.
+   */
+  static $cache = [];
+
   /**
    * {@inheritdoc}
    */
@@ -108,19 +114,36 @@ class EntityReferenceRevisionsFieldItemList extends EntityReferenceFieldItemList
    * {@inheritdoc}
    */
   public function hasAffectingChanges(FieldItemListInterface $original_items, $langcode) {
+    // Create a cache key based on entity type, entity id, and langcode.
+    $cache_key = "{$this->getEntity()->getEntityTypeId()}:{$this->getEntity()->id()}:$langcode";
+
+    // If entity exists in cache, return cached value.
+    if (isset(self::$cache[$cache_key])) {
+      return self::$cache[$cache_key];
+    }
+
+    // Set cached value to FALSE until proven otherwise.
+    self::$cache[$cache_key] = FALSE;
+
     // If there are fewer items, then it is a change.
     if (count($this) < count($original_items)) {
+      // We were wrong, the entity has been changed. Update cached value to TRUE and return.
+      self::$cache[$cache_key] = TRUE;
       return TRUE;
     }
 
     foreach ($this as $delta => $item) {
       // If this is a different entity, then it is an affecting change.
       if (!$original_items->offsetExists($delta) || $item->target_id != $original_items[$delta]->target_id) {
+        // We were wrong, the entity has been changed. Update cached value to TRUE and return.
+        self::$cache[$cache_key] = TRUE;
         return TRUE;
       }
       // If it is the same entity, only consider it as having affecting changes
       // if the target entity itself has changes.
       if ($item->entity && $item->entity->hasTranslation($langcode) && $item->entity->getTranslation($langcode)->hasTranslationChanges()) {
+        // We were wrong, the entity has been changed. Update cached value to TRUE and return.
+        self::$cache[$cache_key] = TRUE;
         return TRUE;
       }
     }
@@ -128,4 +151,11 @@ class EntityReferenceRevisionsFieldItemList extends EntityReferenceFieldItemList
     return FALSE;
   }
 
+  /**
+   * {@inheritdoc }
+   */
+  public function postSave($update) {
+    // Reset static cache to break circuclar dependency after completing a save.
+    self::$cache = [];
+  }
 }