func main() {
	r, err := git.PlainClone("/tmp/foo", false, &git.CloneOptions{
		URL:      "https://github.com/go-git/go-git",
		Progress: os.Stdout,
	})
	if err != nil {
		log.Println(err.Error())
		return
	}
	// SUCCESS
	h, err := r.ResolveRevision("cded5b6")
	if err != nil {
		log.Println("ResolveRevision", err)
		return
	}
	log.Println(h)
	r, err = git.PlainOpen("/tmp/foo")
	if err != nil {
		log.Println(err.Error())
		return
	}
	// FAILED：reference not found
	h, err = r.ResolveRevision("cded5b6")
	if err != nil {
		log.Println("ResolveRevision", err)
		return
	}
	log.Println(h)
}