code: func BuilderIDLink(b, project string) string {
  	parts := strings.Split(b, "/")
  	if len(parts) != 3 {
  		return InvalidBuilderIDURL
  	}
  
  	switch source := parts[0]; source {
  	case "buildbot":
  		return fmt.Sprintf("/buildbot/%s/%s", parts[1], parts[2])
  	case "buildbucket":
  		return fmt.Sprintf("/p/%s/builders/%s/%s", project, parts[1], parts[2])
  	default:
  		return InvalidBuilderIDURL
  	}
  }
docs: // BuilderIDLink gets a builder link from builder ID and project.
  // Depends on routes.go.