code: func hasGopathPrefix(file, gopath string) (hasGopathPrefix bool, prefixLen int) {
  	gopathWorkspaces := filepath.SplitList(gopath)
  	for _, gopathWorkspace := range gopathWorkspaces {
  		gopathWorkspace = filepath.Clean(gopathWorkspace)
  		if strings.HasPrefix(file, gopathWorkspace) {
  			return true, len(gopathWorkspace)
  		}
  	}
  	return false, 0
  }
docs: // hasGopathPrefix returns true and the length of the matched GOPATH workspace,
  // iff file has a prefix that matches one of the GOPATH workspaces.