code: func (sis *SegmentInfos) nextSegmentFilename() string {
  	var nextGeneration int64
  	if sis.generation == -1 {
  		nextGeneration = 1
  	} else {
  		nextGeneration = sis.generation + 1
  	}
  	return util.FileNameFromGeneration(util.SEGMENTS, "", nextGeneration)
  }
docs: /* Get the next segments_N filename that will be written. */