"type" and "view-mode" attributes are removed from default output

In version 2, custom elements for entities had "type" and "view-mode" attributes output by default (added by CustomElementsGenerator::getEntityDefaults()), though the "view-mode" attribute was only output in HTML format, and suppressed in JSON format.

In version 3, these are not output by default.

Customizing defaults

To add these attributes back to output:

• Either add them explicitly as fields in a custom elements display,
• Or, when having Layout Builder enabled or you want to keep your custom processor code (i.e. in version 3, your custom elements displays have "Automatic processing" enabled): Add them back in an alter hook:
  

  function MYMODULE_custom_element_entity_alter(CustomElement $custom_element, ContentEntityInterface $entity, string $viewMode) {
    if (!$custom_element->getAttribute('type')) {
      $custom_element->setAttribute('type', $entity->bundle());
    }
    // This was likely not present in JSON output / is only necessary for HTML:
    if (!$custom_element->getAttribute('view-mode')) {
      $element->setAttribute('view-mode', $viewMode);
    }
  }
  

If most of your entities are built through the standard processor code in version 2 (DefaultContentEntityProcessor), there's another way instead of the alter hook above (though its advantages over the alter hook ar unclear):

• Make sure a custom elements display exists with name == the entity type, and "Automatic processing" enabled, for all relevant entities/bundles.
• Add the following class to your module:
  

  namespace Drupal\MY_MODULE\Processor;
  
  use Drupal\custom_elements\CustomElement;
  use Drupal\custom_elements\Processor\DefaultContentEntityProcessor;
  
  class V2DefaultContentEntityProcessor extends DefaultContentEntityProcessor {
  
    public function addtoElement($data, CustomElement $element, $viewMode, $key = '') {
      // Add attributes that were standard in custom_elements v2.
      if ($data->bundle() != $data->getEntityTypeId()) {
        $element->setAttribute('type', $data->bundle());
      }
      // This was likely not present in JSON output / is only necessary for HTML:
      $element->setAttribute('view-mode', $viewMode);
      parent::addtoElement($data, $element, $viewMode, $key);
    }
  
  }
  

• Add in your services.yml file:
  

  services:
    # Override custom_elements default, priority + 1
    MY_MODULE.processor.default_content_entity:
      class: Drupal\MY_MODULE\Processor\V2DefaultContentEntityProcessor
      tags:
        - { name: custom_elements_processor, priority: -99 }