Qt for WebAssembly and exceptions

jborys

Hi I have been exploring with Qt for WebAssembly to help me learn more about the WebAssembly platform.

One thing that I cannot for the life of me figure out is how to enable exceptions using Qt's infrastructure?

Example project:

# CMakeLists.txt
cmake_minimum_required(VERSION 3.22)
project(learnWebAssembly VERSION 0.1.0)

include(CTest)
enable_testing()

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

find_package(Qt6 6.4.0 REQUIRED COMPONENTS Core Qml Gui CMAKE_FIND_ROOT_PATH_BOTH)

add_compile_options(-fexceptions -sNO_DISABLE_EXCEPTION_CATCHING)
add_link_options(
  "SHELL:-fexceptions"
  "SHELL:-sLLD_REPORT_UNDEFINED"
  "SHELL:-sNO_DISABLE_EXCEPTION_CATCHING"
  "SHELL:-sLIBRARY_DEBUG=1"
  "SHELL:-sSYSCALL_DEBUG=1"
  # "SHELL:-sFS_LOG=1"
  "SHELL:-sSOCKET_DEBUG"
)

qt_add_executable(exceptions_example exceptions-example.cpp)

set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)

// example-exceptions.cpp
#include <stdio.h>

int main() {
  try {
    puts("throw...");
    throw 1;
    puts("(never reached)");
  } catch(...) {
    puts("catch!");
  }
  return 0;
}

When I compile this using CMake I get the error:

Exception catching is disabled, this exception cannot be caught. Compile with -sNO_DISABLE_EXCEPTION_CATCHING or -sEXCEPTION_CATCHING_ALLOWED=[..] to catch.

but when I compile this file according to the webassembly documentation I can catch exceptions according to the docs? https://emscripten.org/docs/porting/exceptions.html?highlight=fexception

Outstanding questions:

If I use a release build of Qt for WebAssembly does that override any of my explicit exception handling flags set at compile time?
Do I need to use a debug build of Qt for WebAssembly then to catch exceptions?

Thanks for taking the time to read this!