class FieldListOptions

class FieldListOptions extends OptionsProviderBase implements ContainerInjectionInterface {
  
  /**
   * The entity field manager service.
   *
   * @var \Drupal\Core\Entity\EntityFieldManagerInterface
   */
  protected $entityFieldManager;
  
  /**
   * Constructs a FieldListOptions object.
   *
   * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
   *   The entity field manager service.
   */
  public function __construct(EntityFieldManagerInterface $entity_field_manager) {
    $this->entityFieldManager = $entity_field_manager;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('entity_field.manager'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function getPossibleOptions(AccountInterface $account = NULL) {
    $options = [];
    // Load all the fields in the system.
    $fields = $this->entityFieldManager
      ->getFieldMap();
    // Add each field to our options array.
    foreach ($fields as $entity_fields) {
      foreach ($entity_fields as $field_name => $field) {
        $options[$field_name] = $field_name . ' (' . $field['type'] . ')';
      }
    }
    // Sort the result by value for ease of locating and selecting.
    asort($options);
    return $options;
  }

}