text: /*
   * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
   * or more contributor license agreements. Licensed under the Elastic License;
   * you may not use this file except in compliance with the Elastic License.
   */
  
  export function getFieldNames(names, arg) {
    if (arg.args != null) {
      return names.concat(arg.args.reduce(getFieldNames, []));
    }
  
    if (typeof arg === 'string') {
      return names.concat(arg);
    }
  
    return names;
  }
  