Function lua_setupvalue

3rd/lua-5.4.3/src/lapi.c:1390–1406

LUA_API const char *lua_setupvalue (lua_State *L, int funcindex, int n) {
  const char *name;
  TValue *val = NULL;  /* to avoid warnings */
  GCObject *owner = NULL;  /* to avoid warnings */
  TValue *fi;
  lua_lock(L);
  fi = index2value(L, funcindex);
  api_checknelems(L, 1);
  name = aux_upvalue(fi, n, &val, &owner);
  if (name) {
    L->top--;
    setobj(L, val, s2v(L->top));
    luaC_barrier(L, owner, val);
  }
  lua_unlock(L);
  return name;
}


static UpVal **getupvalref (lua_State *L, int fidx, int n, LClosure **pf) {