code: func (fd *finder) findAllGoFiles(dir string) ([]string, error) {
  	var err error
  	var names []string
  	oncer.Do(fd.key("findAllGoFiles", dir), func() {
  		plog.Debug(fd, "findAllGoFiles", "dir", dir)
  
  		callback := func(path string, do *godirwalk.Dirent) error {
  			ext := filepath.Ext(path)
  			if ext != ".go" {
  				return nil
  			}
  			names = append(names, path)
  			return nil
  		}
  		err = godirwalk.Walk(dir, &godirwalk.Options{
  			FollowSymbolicLinks: true,
  			Callback:            callback,
  		})
  	})
  
  	return names, err
  }
docs: // findAllGoFiles *.go files for a given diretory