code: func (d *ResourceDiff) UpdatedKeys() []string {
  	var s []string
  	for k := range d.updatedKeys {
  		s = append(s, k)
  	}
  	for k := range d.forcedNewKeys {
  		for _, l := range s {
  			if k == l {
  				break
  			}
  		}
  		s = append(s, k)
  	}
  	return s
  }
docs: // UpdatedKeys returns the keys that were updated by this ResourceDiff run.
  // These are the only keys that a diff should be re-calculated for.
  //
  // This is the combined result of both keys for which diff values were updated
  // for or cleared, and also keys that were flagged to be re-diffed as a result
  // of ForceNew.