Crash in luabridge::Stack<int>::get

[liuaifu]

The type of the value at index -1 is double.

auto is_int = luabridge::Stack<int>::isInstance(L, -1);    // true
auto value = luabridge::Stack<int>::get(L, -1);            // crash

I'm using Lua v5.4.4 and LuaBridge v2.7.207 on Windows 10.

[dmitry-t]

This is not clearly stated in the documentation but Lua 5.3 and 5.4 are unsupported.
At least without any 5.3 and 5.4 tests we cannot proof they are supported.

[stefanfrings]

I can reproduce the issue in my environment as well.

• most recent LuaBridge
• Lua 5.4.2
• g++ 10.3.0 on Windows 10 with msys2

lua_State* lua = luaL_newstate();

luabridge::Stack<double>::push(lua, 23.24);

// returns true
std::cout << luabridge::Stack<int>::isInstance(lua, -1) << std::endl;
std::cout << luabridge::Stack<unsigned int>::isInstance(lua, -1) << std::endl;
std::cout << luabridge::Stack<float>::isInstance(lua, -1) << std::endl;
std::cout << luabridge::Stack<double>::isInstance(lua, -1) << std::endl;

// returns false
std::cout << luabridge::Stack<char>::isInstance(lua, -1) << std::endl;
std::cout << luabridge::Stack<std::optional<int>>::isInstance(lua, -1) << std::endl;
std::cout << luabridge::Stack<std::string>::isInstance(lua, -1) << std::endl;

lua_close(lua);

The return value of isInstance shall only be true if get can be executed successful. It is somehow related to the issue #251 (comment).

Unfortunately the issue can't be solved because the affected isInstance functions make use of lua_type which can't distinguish between different number types. The check for all affected types is as following.
return lua_type(L, index) == LUA_TNUMBER;

This issue applies to different Lua versions. I've explicitly checked Lua 5.2 and 5.4.

https://www.lua.org/manual/5.2/manual.html
https://www.lua.org/manual/5.4/manual.html

The issue can be solved with Lua 5.2+. There are the functions lua_tointegerx and lua_tonumberx available.

[dmitry-t]

So I've checked the behavior.
The isInstance<int>() returns true while it should return false.
The Stack<int>::get() crash would basically be expected if it returned false.

[dmitry-t]

Please take a look at the #292.
An interesting fact that in Lua 5.1 and Lua 5.2 we cannot quickly check if the value on the stack is integer, however a float value is successfully converted into an integer.
This is what I mentioned earlier: if isInstance says true, then get should work.

[kunitoki]

You can support integers across all lua versions, see https://github.com/kunitoki/LuaBridge3/blob/master/Source/LuaBridge/detail/LuaHelpers.h#L90

[kunitoki]

Stack::get cannot be safely called from C++ as it's raising lua_error (it calls the lua panic handler which will throw with exceptions on but will std::abort without exceptions, which is not acceptable). Because of that we would need to use a safe get method not calling lua_error but returning something like c++23 std::expected (which in turn can be handled to call lua_error only when invoked from lua).