https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110171
Bug ID: 110171
Summary: [[nodiscard]] of await_resume ignored when discarding
result of co_await expression
Product: gcc
Version: 11.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: lukaslang.bugtracker at outlook dot com
Target Milestone: ---
(Note: The example & bug is very similar to this here:
https://developercommunity.visualstudio.com/t/nodiscard-not-honored-by-co_await/1500944)
It seems that discarding the `co_await`ed result of an awaitable with
`[[nodiscard]]` `await_resume` doesn't lead to the expected warning
([Godbolt](https://godbolt.org/z/o47EdzMj8)):
```
#include <coroutine>
struct must_check_result
{
bool await_ready() { return false; }
void await_suspend(std::coroutine_handle<>) {}
[[nodiscard]] bool await_resume() { return {}; }
};
struct task {};
namespace std
{
template<typename... Args>
struct coroutine_traits<task, Args...>
{
struct promise_type
{
task get_return_object() { return {}; }
suspend_always initial_suspend() noexcept { return {}; }
suspend_always final_suspend() noexcept { return {}; }
void return_void() {}
void unhandled_exception() {}
};
};
}
task example()
{
co_await must_check_result(); // no warning even though await_ready is
marked [[nodiscard]]
must_check_result().await_resume();
}
```
