`xcpp::clear_output` does not clear exception messages

[AntoinePrv]

I am unsure how to reproduce this without xwidgets.

Minimal example (Can be tried here).

• Change value to 0, 1, 2, 3, everything going as planned;
• Set value to 33, an exception message is shown;
• Change value to 0, the exception message is not cleared.
• Change value to 1, the message for 0 is cleared, the exception message is not cleared.

#include <iostream>
#include <stdexcept>
#include <xwidgets/xall.hpp>
#include <xcpp/xdisplay.hpp>


auto num = xw::number<std::uint32_t>();
auto out = xw::output();

XOBSERVE(num, value, [&](const auto& s) {
    auto g = out.guard();
    xcpp::clear_output();
    if(s.value() == 33){
        throw std::runtime_error("Exception");
    }

    std::cout << "Value: " << s.value() << std::endl;
});

xcpp::display(num);
xcpp::display(out);

[anutosh491]

I'll try this out soon. Haven't had any problems with xcpp::clear_output just yet !

[anutosh491]

cc @AntoinePrv

Yes, xcpp::clear_output() can’t reliably clear that comm-level error banner. It clears the cell output area (stream/display outputs associated with the cell execution). The bad message … Message type: comm_msg is emitted because the comm handler hit an exception/unregistered comm, and that’s not part of the same output stream that clear_output controls.

So probably can put something like this to use I guess !

#include <iostream>
#include <stdexcept>
#include <xwidgets/xall.hpp>
#include <xcpp/xdisplay.hpp>

auto num = xw::number<std::uint32_t>();
auto out = xw::output();

XOBSERVE(num, value, [&](const auto& s) {
    auto g = out.guard();

    xcpp::clear_output();

    try {
        if (s.value() == 33) throw std::runtime_error("Exception");
        std::cout << "Value: " << s.value() << std::endl;
    } catch (const std::exception& e) {
        std::cout << "Caught: " << e.what() << std::endl;
    }
});

xcpp::display(num);
xcpp::display(out);