Coroutine final_suspend is not noexcept

[joemmett]

The final_suspend() functions and await_suspend() functions of the enclosed awaitable class are not noexcept in coroutine_support.ipp. The co_await expression for the final suspend point is required to be non-throwing by the standard.

The current implementation resumes the continuation (if there is one) in await_suspend(), so this is not necessarily quite just as simple as making it noexcept. Having await_suspend() return the continuation handle instead of directly resuming it would make it easier to make this noexcept.

[ned14]

Nice catch, thanks!

[ned14]

Can you look, and ideally, test f913c7e to see if it solves this? I don't have a compiler to hand able to test this code, so this patchset is pure guesswork.

[joemmett]

Thanks! I tried it out with a development branch build of MSVC and it's currently failing the coroutine test because lazy_await is directly using await_suspend and await_resume instead of co_awaiting it, so there is no compiler-generated resume of the returned handle. This trips the assertion that result_set has been set.

This could be solved with something like:

  auto lazy_await = [](auto t) {
#if OUTCOME_HAVE_NOOP_COROUTINE
    t.await_suspend({}).resume();
#else
    t.await_suspend({});
#endif
    return t.await_resume();
  };

[ned14]

Ok, fixed as you suggest. Thanks for your help in fixing this!