Missing message for C++ exceptions in certain lambdas and function objects

[firas-assaad]

Hi!

This might be is related to my last issue #906

For free C++ lambdas that capture variables and throw exceptions, the exception's what() message isn't returned in the sol error. Instead I might get something from the stack. If the lambda doesn't capture anything then everything works as expected.

This doesn't seem to be happen for lambdas registered on user types, but only when they're registered as global Lua functions. The error message returned when the function is wrapped in sol::yielding is slightly different, but the same issue occurs with or without sol::yielding.

I'm using Visual Studio 2019, latest sol single header (revision 82812c5 generated 2020-03-31 04:18:51.740568 UTC).

#define SOL_USING_CXX_LUA 1
#define SOL_ALL_SAFETIES_ON 1
#define SOL_EXCEPTIONS_ALWAYS_UNSAFE 1
#include <sol.hpp>
#include <iostream>
#include <exception>

int main() {
    try {
        sol::state lua;
        lua.open_libraries(sol::lib::base, sol::lib::coroutine);

        int x = 5;
        lua["f"] = [x](const std::string& text) {
            throw std::exception{"expected"};
        };

        sol::string_view code = R"(f("hi"))";
        auto result = lua.safe_script(code);
        if (!result.valid()) {
            sol::error err = result;
            throw std::runtime_error(err.what());
        }
    } catch (std::exception& e) {
        std::cout << "Exception: " << e.what() << "\n";
    }
}

This is what I get:

[sol3] An error occurred and has been passed to an error handler: sol: CRITICAL_EXCEPTION_FAILURE error: hi
Exception: sol: CRITICAL_EXCEPTION_FAILURE error: hi

This is what I expect:

[sol3] An exception occurred: expected
[sol3] An error occurred and has been passed to an error handler: sol: runtime error: expected
stack traceback:
        [C]: in function 'f'
        [string "f("hi")"]:1: in main chunk
Exception: sol: runtime error: expected
stack traceback:
        [C]: in function 'f'
        [string "f("hi")"]:1: in main chunk

I also noticed the same issue when using function objects:

#define SOL_USING_CXX_LUA 1
#define SOL_ALL_SAFETIES_ON 1
#define SOL_EXCEPTIONS_ALWAYS_UNSAFE 1
#include <sol.hpp>
#include <iostream>
#include <exception>

class functor {
public:
    void operator()(const std::string& message) {
        throw std::exception{"expected"};
    }
};

int main() {
    try {
        sol::state lua;
        lua.open_libraries(sol::lib::base, sol::lib::coroutine);

        functor f;
        lua["f"] = f;

        sol::string_view code = R"(f("hi"))";
        auto result = lua.safe_script(code);
        if (!result.valid()) {
            sol::error err = result;
            throw std::runtime_error(err.what());
        }
    } catch (std::exception& e) {
        std::cout << "Exception: " << e.what() << "\n";
    }
}

[ThePhD]

I guess I have to proof the exception code.

For like the 8th time.

Oh booooy....!

[firas-assaad]

Hi, I was investigating a similar error and found that by commenting out the catch(...) in trampoline.hpp I get the expected detailed message. It'll probably break something else, so I'm not sure if this helps in any way.

[ThePhD]

Part of the #1260 fixes now.