func addPrevious(sh *shell.Shell, h string, c string) (string, error) {
cur, err := sh.ResolvePath(c)
if err != nil {
log.Fatalf("could not resolve current version: %s", err)
}
prev, err := sh.ResolvePath(c + "/previous")
if err == nil {
h, err = sh.PatchLink(h, "previous", prev, true)
if err != nil {
return "", err
}
}
if h != cur {
h, err = sh.PatchLink(h, "previous", cur, true)
if err != nil {
return "", err
}
}
return h, nil
}
