覆盖 require 后调用 `lua_getfield()` 时崩溃答案

【问题标题】：Crashes when calling `lua_getfield()` after overriding the require覆盖 require 后调用 `lua_getfield()` 时崩溃
【发布时间】：2019-01-02 09:06:03
【问题描述】：

这个问题与@Henri_Menke 对此问题的回答有关：How to get preloaded module name in C++

我正在尝试用我自己的版本覆盖 require 函数，以便我可以在 Lua 脚本中获取预加载的模块名称。

这是我的代码：

#include "lua.hpp"

void main()
{
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);
    lua_settop(L, 0);
    luaL_dostring(L, "local require_original = require\n"
                     "function require(name, ...)\n"
                         "current_module = name\n"
                         "require_original(name, ...)\n"
                         "current_module = nil\n"
                     "end\n"); //if I comment out this chunk, it works fine
    luaL_dostring(L, "package.preload['test'] = function ()\n"
                         "local test = {}\n"
                         "print('While loading:', current_module)\n"
                         "function test.update() print('Updated!') end\n"
                         "return test\n"
                     "end\n");
    lua_getglobal(L, "require");
    lua_pushstring(L, "test");
    if (lua_pcall(L, 1, LUA_MULTRET, 0))
    {
        std::cout << "Error: " << lua_tostring(L, -1) << std::endl;
        lua_pop(L, 1);
    }
    int top = lua_gettop(L);
    lua_getfield(L, -1, "update"); //crashes here
    if (lua_isfunction(L, -1))
    {
        lua_pushnil(L);
        if (lua_pcall(L, 1, LUA_MULTRET, 0))
        {
            std::cout << "Error: " << lua_tostring(L, -1) << std::endl;
            lua_pop(L, 1);
        }
    }
    lua_close(L);
}

但是，调用lua_getfield(L, -1, "update"); 时它会崩溃。

当我注释掉 Lua 脚本的第一块时，它不再崩溃（第一个 luaL_dostring）。

如果我使用自己的require 版本，我不明白为什么它会崩溃。

我该如何解决这个问题？

【问题讨论】：

你自定义的require函数需要返回模块。

标签： c++ lua require

【解决方案1】：

我忘记从覆盖的require 函数返回模块表。对此感到抱歉。

#include <iostream>
#include "lua.hpp"

int main() {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);
    lua_settop(L, 0);
    luaL_dostring(L, "local require_original = require\n"
                     "function require(name, ...)\n"
                         "current_module = name\n"
                         "local val = table.pack(require_original(name, ...))\n"
                         "current_module = nil\n"
                         "return table.unpack(val,1,val.n)\n"
                     "end\n"); //if I comment out this chunk, it works fine
    luaL_dostring(L, "package.preload['test'] = function ()\n"
                         "local test = {}\n"
                         "print('While loading:', current_module)\n"
                         "function test.update() print('Updated!') end\n"
                         "return test\n"
                     "end\n");
    lua_getglobal(L, "require");
    lua_pushstring(L, "test");
    if (lua_pcall(L, 1, LUA_MULTRET, 0))
    {
        std::cout << "Error: " << lua_tostring(L, -1) << std::endl;
        lua_pop(L, 1);
    }
    int top = lua_gettop(L);
    lua_getfield(L, -1, "update"); //crashes here
    if (lua_isfunction(L, -1))
    {
        lua_pushnil(L);
        if (lua_pcall(L, 1, LUA_MULTRET, 0))
        {
            std::cout << "Error: " << lua_tostring(L, -1) << std::endl;
            lua_pop(L, 1);
        }
    }
    lua_close(L);
}

$ clang++ -Wall -Wextra -Wpedantic -I /usr/include/lua5.2 test.cpp -llua5.2
test.cpp:28:9: warning: unused variable 'top' [-Wunused-variable]
    int top = lua_gettop(L);
        ^
1 warning generated.
$ ./a.out 
While loading:  test
Updated!

【讨论】：