不能将Lua编译为C++

Question

我试图使用以下CMakeLists.txt (和CMake 3.21)构建Lua5.4.3(编写本文时的最新版本)(忽略目标名为lua_static，尽管它是一个共享库)：

cmake_minimum_required(VERSION 3.16)

project(Lua LANGUAGES CXX)

# make cache variables for install destinations
include(GNUInstallDirs)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)

set(LUA_LIB_SRCS 
    "src/ldblib.c"
    "src/ldebug.c"
    "src/ldo.c"
    "src/ldump.c"
    "src/lfunc.c"
    "src/lgc.c"
    "src/linit.c"
    "src/liolib.c"
    "src/lopcodes.c"
    "src/llex.c"
    "src/lmathlib.c"
    "src/lmem.c"
    "src/loadlib.c"
    "src/lobject.c"
    "src/loslib.c"
    "src/lparser.c"
    "src/lstate.c"
    "src/lstring.c"
    "src/lstrlib.c"
    "src/ltable.c"
    "src/ltablib.c"
    "src/ltm.c"
    "src/lundump.c"
    "src/lutf8lib.c"
    "src/lvm.c"
    "src/lzio.c"
    "src/lapi.c"
    "src/lauxlib.c"
    "src/lbaselib.c"
    "src/lcode.c"
    "src/lcorolib.c"
    "src/lctype.c"
)

set(LUA_HEADERS_INSTALL
    "src/lua.h"
    "src/luaconf.h"
    "src/lualib.h"
    "src/lauxlib.h"
    "src/lua.hpp"
)

# Compile directly as C++.
set_source_files_properties(${LUA_LIB_SRCS} PROPERTIES LANGUAGE CXX )

add_library(lua_static SHARED ${LUA_LIB_SRCS})
set_target_properties(lua_static PROPERTIES LINKER_LANGUAGE CXX)
set_target_properties(lua_static PROPERTIES DEBUG_POSTFIX d)

# make sure __cplusplus is defined when using msvc
if (MSVC)
    target_compile_options(lua_static PRIVATE /TP       # /TP doesn't is somehow stripped or ignored?
                                       /Zc:__cplusplus)
endif ()

target_include_directories(lua_static
                           PUBLIC
                           "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
)

install(TARGETS lua_static
        EXPORT lua_static_targets
        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
        RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
        INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
)

install(FILES ${LUA_HEADERS_INSTALL} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})

install(EXPORT lua_static_targets
        FILE LuaStaticTargets.cmake
        NAMESPACE lua::
        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/lua
)

include(CMakePackageConfigHelpers)

configure_package_config_file(${CMAKE_CURRENT_SOURCE_DIR}/Config.cmake.in
  "${CMAKE_CURRENT_BINARY_DIR}/LuaConfig.cmake"
  INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/lua
)

install(FILES
          "${CMAKE_CURRENT_BINARY_DIR}/LuaConfig.cmake"
        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/lua
)

在使用MSVC进行构建时，定义了__cplusplus，因此，在此之前，我假设所有的事情都能按预期工作。安装之后，我将链接到库，如下所示

cmake_minimum_required(VERSION 3.16)
project(TestProject)

add_executable(Test Main.cpp)

# Lua
find_package(lua REQUIRED PATHS ${CMAKE_CURRENT_LIST_DIR}/lua)
set_target_properties(lua::lua_static PROPERTIES LINKER_LANGUAGE CXX)
target_link_libraries(Test lua::lua_static)

我希望将Lua编译为C++的原因是为了启用异常(而不是longjmp)。因此，为了测试是否会引发异常，我尝试在这个测试程序中调用一个

#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

#include <iostream>

constexpr char* Test_Lua = R"(
function f (x, y)
      unknown()
      return 1/0
en
)";

lua_State* state;

int main(int argc, char* argv[])
{
    state = luaL_newstate();
    luaL_openlibs(state);

    try
    {
        int error = luaL_loadbuffer(state, Test_Lua, strlen(Test_Lua), "Test");
        lua_call(state, 0, LUA_MULTRET); // Should thow, because of the syntax error
    }
    catch (...)
    {
        std::cout << "Exception!" << std::endl;
        goto end;
    }

end:
    lua_close(state);
    return 0;
}

当使用调试器进入lua_call时，我最终会进入ldo.c，其中Visual表示LUAI_THROW不是通过C++ exeption处理来定义的。这是因为没有定义__cplusplus。跳转到前面创建的Lua项目文件中的源文件时，LUAI_THROW被定义为理想的。我可以包含Lua头的事实告诉我，这个库已经编译成了一个C++库。事实上，如果我试图添加extern "C" { ... }，我就会得到链接器错误。

有人能找出问题的原因吗？

编辑：

在深入研究这个问题之后，我意识到所有编译都像C++一样，就是Lua 内部处理通过异常返回错误代码(如luaL_loadbuffer)的函数。这并不意味着我可以抓住并处理它们(这是我最初认为的)。像lua_call这样的函数在不受保护的模式下运行，因此调用恐慌函数(见@bremen_matt's post)。

Answer 1

我对Lua一无所知。别挡道..。

我想你错过了一些关于Lua内部工作的东西。如果我在大约第57行修改ldo.c中的宏，可以读到：

#include <iostream>
#define LUAI_THROW(L,c) (fprintf(stderr, "THROWING\n"), throw(c))
#define LUAI_TRY(L,c,a) \
    try { a } catch(...) { fprintf(stderr, "CAUGHT\n"); if ((c)->status == 0) (c)->status = -1; }

然后，当我运行它时，我看到了输出：

THROWING
CAUGHT
PANIC: unprotected error in call to Lua API (attempt to call a string value)

这意味着Lua在内部试图运行代码片段，捕获异常，然后退出而不引发另一个异常。因此，您作为用户无法捕获此异常。它正在卢阿的体内被消耗掉。

简单地看一看代码，就会发现您可能想使用lua_pcall。似乎p的意思是protected？你可以做一些错误处理吗？无论哪种方式，该函数似乎也不会将错误抛得更高。似乎您必须传递一个用于错误处理的函数。