class BundleConfigImportValidate

class BundleConfigImportValidate extends ConfigImportValidateEventSubscriberBase {

  /**
   * The config manager.
   *
   * @var \Drupal\Core\Config\ConfigManagerInterface
   */
  protected $configManager;

  /**
   * The entity type manager service.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * Constructs the event subscriber.
   *
   * @param \Drupal\Core\Config\ConfigManagerInterface $config_manager
   *   The config manager.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager service.
   */
  public function __construct(ConfigManagerInterface $config_manager, EntityTypeManagerInterface $entity_type_manager) {
    $this->configManager = $config_manager;
    $this->entityTypeManager = $entity_type_manager;
  }

  /**
   * Ensures bundles that will be deleted are not in use.
   *
   * @param \Drupal\Core\Config\ConfigImporterEvent $event
   *   The config import event.
   */
  public function onConfigImporterValidate(ConfigImporterEvent $event) {
    foreach ($event
      ->getChangelist('delete') as $config_name) {

      // Get the config entity type ID. This also ensure we are dealing with a
      // configuration entity.
      if ($entity_type_id = $this->configManager
        ->getEntityTypeIdByName($config_name)) {
        $entity_type = $this->entityTypeManager
          ->getDefinition($entity_type_id);

        // Does this entity type define a bundle of another entity type.
        if ($bundle_of = $entity_type
          ->getBundleOf()) {

          // Work out if there are entities with this bundle.
          $bundle_of_entity_type = $this->entityTypeManager
            ->getDefinition($bundle_of);
          $bundle_id = ConfigEntityStorage::getIDFromConfigName($config_name, $entity_type
            ->getConfigPrefix());
          $entity_query = $this->entityTypeManager
            ->getStorage($bundle_of)
            ->getQuery();
          $entity_ids = $entity_query
            ->condition($bundle_of_entity_type
            ->getKey('bundle'), $bundle_id)
            ->accessCheck(FALSE)
            ->range(0, 1)
            ->execute();
          if (!empty($entity_ids)) {
            $entity = $this->entityTypeManager
              ->getStorage($entity_type_id)
              ->load($bundle_id);
            $event
              ->getConfigImporter()
              ->logError($this
              ->t('Entities exist of type %entity_type and %bundle_label %bundle. These entities need to be deleted before importing.', [
              '%entity_type' => $bundle_of_entity_type
                ->getLabel(),
              '%bundle_label' => $bundle_of_entity_type
                ->getBundleLabel(),
              '%bundle' => $entity
                ->label(),
            ]));
          }
        }
      }
    }
  }

}