Widgets / formatters should return unwrapped $elements

Similar : #2151699: Move #access responsibility from formatters/widgets to EntityViewDisplay/EntityFormDisplay

Cool!

1. +++ b/core/modules/entity/lib/Drupal/entity/Entity/EntityViewDisplay.php
   @@ -231,7 +231,7 @@ public function buildMultiple(array $entities) {
   -          $build[$key] += $formatter->view($items);
   +          $build[$key] += array($field_name => $formatter->view($items));
   

   Minor: it would be slightly clearer to do
   $build[$key][$field_name] = $formatter->view();

2. +++ b/core/modules/field/field.attach.inc
   +++ b/core/modules/field/field.attach.inc
   @@ -91,20 +91,13 @@ function field_invoke_method($method, $target_function, EntityInterface $entity,
   
   @@ -91,20 +91,13 @@ function field_invoke_method($method, $target_function, EntityInterface $entity,
        $target = call_user_func($target_function, $field_definition);
    
        if (method_exists($target, $method)) {
   -      $items = $entity->get($field_definition->getName());
   +      $field_name = $field_definition->getName();
   +      $items = $entity->get($field_name);
          $items->filterEmptyItems();
    
          $result = $target->$method($items, $a, $b);
   -
          if (isset($result)) {
   -        // For methods with array results, we merge results together.
   -        // For methods with scalar results, we collect results in an array.
   -        if (is_array($result)) {
   -          $return = array_merge($return, $result);
   -        }
   -        else {
   -          $return[] = $result;
   -        }
   +        $return[$field_name] = $result;
   

   Hah - true, a bit tedious.
   That function is going away in #2095195: Remove deprecated field_attach_form_*() anyway, at which point it's going to be up to EntityFormDisplay to add the $field_name key (like EntityViewDisplay does here)

Once 1. above is changed, this is RTBC IMO.

Thanks !