static void fieldsel (LexState *ls, expdesc *v) {
  /* fieldsel -> ['.' | ':'] NAME */
  FuncState *fs = ls->fs;
  expdesc key;
  luaK_exp2anyregup(fs, v);
  luaX_next(ls);  /* skip the dot or colon */
  codename(ls, &key);
  luaK_indexed(fs, v, &key);
}