code: func (p *printer) MaybeLeadingComments(ptr interface{}) {
  	comments := p.sourceCodeInfo[ptr].GetLeadingComments()
  	// print comments, but insert "//" before each newline.
  	for len(comments) > 0 {
  		var toPrint string
  		if lineEnd := strings.Index(comments, "\n"); lineEnd >= 0 {
  			toPrint = comments[:lineEnd+1] // includes newline
  			comments = comments[lineEnd+1:]
  		} else {
  			// actually this does not happen, because comments always end with
  			// newline, but just in case.
  			toPrint = comments + "\n"
  			comments = ""
  		}
  		p.Printf("//%s", toPrint)
  	}
  }
docs: // MaybeLeadingComments prints leading comments of the descriptor proto
  // if found.