trait EntityKeysFieldsTrait in Entity API 8.0

trait EntityKeysFieldsTrait {

  /**
   * Returns the base field definitions for entity keys.
   *
   * @param \Drupal\Core\Entity\ContentEntityTypeInterface $entity_type
   *   The entity type.
   *
   * @return \Drupal\Core\Field\BaseFieldDefinition[]
   */
  protected static function entityKeysBaseFieldDefinitions(ContentEntityTypeInterface $entity_type) {
    $fields = [];
    if ($entity_type
      ->hasKey('id')) {
      $fields[$entity_type
        ->getKey('id')] = BaseFieldDefinition::create('integer')
        ->setLabel(t('ID'))
        ->setReadOnly(TRUE)
        ->setSetting('unsigned', TRUE);
    }
    if ($entity_type
      ->hasKey('uuid')) {
      $fields[$entity_type
        ->getKey('uuid')] = BaseFieldDefinition::create('uuid')
        ->setLabel(t('UUID'))
        ->setReadOnly(TRUE);
    }
    if ($entity_type
      ->hasKey('revision')) {
      $fields[$entity_type
        ->getKey('revision')] = BaseFieldDefinition::create('integer')
        ->setLabel(t('Revision ID'))
        ->setReadOnly(TRUE)
        ->setSetting('unsigned', TRUE);
    }
    if ($entity_type
      ->hasKey('langcode')) {
      $fields[$entity_type
        ->getKey('langcode')] = BaseFieldDefinition::create('language')
        ->setLabel(t('Language'))
        ->setTranslatable(TRUE)
        ->setRevisionable(TRUE)
        ->setDisplayOptions('view', [
        'type' => 'hidden',
      ])
        ->setDisplayOptions('form', [
        'type' => 'language_select',
        'weight' => 2,
      ]);
    }
    $bundle_entity_type_id = $entity_type
      ->getBundleEntityType();
    if ($bundle_entity_type_id && $entity_type
      ->hasKey('bundle')) {
      $fields[$entity_type
        ->getKey('bundle')] = BaseFieldDefinition::create('entity_reference')
        ->setLabel(t('Type'))
        ->setSetting('target_type', $bundle_entity_type_id)
        ->setReadOnly(TRUE);
    }
    return $fields;
  }

}