code: func getSourceLines(file string) [][]byte {
  	fileSources.Lock()
  	defer fileSources.Unlock()
  	if fileSources.lines == nil {
  		fileSources.lines = map[string][][]byte{}
  	}
  	if lines, ok := fileSources.lines[file]; ok {
  		return lines
  	}
  	text, _ := ioutil.ReadFile(file)
  	fileSources.lines[file] = bytes.Split(text, []byte{'\n'})
  	return fileSources.lines[file]
  }
docs: // Reads souce file lines from disk if not cached already.