code: func goFilesIn(dir string) ([]string, error) {
  	pkg, err := build.ImportDir(dir, 0)
  	if err != nil {
  		return nil, fmt.Errorf("cannot process directory %s: %s", dir, err)
  	}
  	var names []string
  	names = append(names, pkg.GoFiles...)
  	names = append(names, pkg.CgoFiles...)
  	names = prefixDirectory(dir, names)
  	return names, nil
  }
docs: // goFilesIn lists .go files in dir.