Notice: Only variables should be passed by reference in PHP 7.1

Problem/Motivation

The following Notice is thrown when migration field_collections in PHP 7.1

Only variables should be passed by reference File \field_collection\field_collection.migrate.inc, line 97

Proposed resolution

In field_collection_item_add() in field_collection.pages.inc we have closely parallel code:

  $result = entity_load($entity_type, array($entity_id));
  $entity = reset($result);
  if (!$entity) {

Model the relevant lines of migrate code on what's in field_collection_item_add().

Further detail: the problem here is in core's entity_load(), which should have returned a single entity but in Drupal 7 returned an array of entities. This was fixed for D8 in #1160566: entity_load() is actually entity_load_multiple(). To partially address this issue, the Entity API module introduced entity_load_single(). Since Entity API is a dependency of Field Collection, we can use it here--in fact, we already are using it, later in this same method. However, the current code sets the $reset argument to TRUE, and entity_load_single() does not pass that argument when it calls entity_load(), meaning that the default, FALSE, will apply. Therefore, we can't use entity_load_single() here.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet