FieldUninstallValidator::validate

public FieldUninstallValidator::validate($module)

public function validate($module) {
  $entity_types = $this->entityManager->getDefinitions();
  $reasons = array();
  foreach ($entity_types as $entity_type) {
    if ($module == $entity_type->getProvider() && $entity_type instanceof ContentEntityTypeInterface && $this->entityManager->getStorage($entity_type->id())->hasData()) {
      $reasons[] = $this->t('There is content for the entity type: @entity_type', array('@entity_type' => $entity_type->getLabel()));
    }
  }
  return $reasons;
}

public function validate($module) {
  $reasons = [];
  if ($field_storages = $this->getFieldStoragesByModule($module)) {
    // Provide an explanation message (only mention pending deletions if there
    // remain no actual, non-deleted fields.)
    $fields_in_use = [];
    foreach ($field_storages as $field_storage) {
      if (!$field_storage->isDeleted()) {
        $fields_in_use[$field_storage->getType()][] = $field_storage->getLabel();
      }
    }
    if (!empty($fields_in_use)) {
      foreach ($fields_in_use as $field_type => $field_storages) {
        $field_type_label = $this->getFieldTypeLabel($field_type);
        $reasons[] = $this->formatPlural(count($fields_in_use[$field_type]), 'The %field_type_label field type is used in the following field: @fields', 'The %field_type_label field type is used in the following fields: @fields', ['%field_type_label' => $field_type_label, '@fields' => implode(', ', $field_storages)]);
      }
    }
    else {
      $reasons[] = $this->t('Fields pending deletion');
    }
  }
  return $reasons;
}