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QCoro::detail::QCoroSignal is not a copy-constructible class (it contains std::unique_ptr), but when calling co_await, gcc tried to make a copy of coroSignal either when evaluating the expression after `co_await`, or when passing the result of the expression to `Task<T>::await_transform()`. This is despite Task::await_transform() having an overload that accepts reference or an lvalue reference to the object. I do believe this might be a regression in gcc 11.3, since it worked in gcc 11.2 and it works with clang as well. The C++ standard does not specify any constraints regarding how the result of the expression after the co_await keyword should be passed to `await_transform`. As a workaround, we co_await a temporary QCoroSignal, which gcc seems to correctly pass down as a lvalue reference, so no issues with copying. Explictly `std::move()`ing `coroSignal` to `co_await` would also work, but it's weird. I haven't confirmed whether this is a bug yet, as I first need to put together a small reproducer case.
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QCoro::detail::QCoroSignal is not a copy-constructible class
(it contains std::unique_ptr), but when calling co_await,
gcc tried to make a copy of coroSignal either when evaluating
the expression after
co_await, or when passing the result ofthe expression to
Task<T>::await_transform(). This is despiteTask::await_transform() having an overload that accepts reference
or an lvalue reference to the object.
I do believe this might be a regression in gcc 11.3, since it worked
in gcc 11.2 and it works with clang as well. The C++ standard does
not specify any constraints regarding how the result of the expression
after the co_await keyword should be passed to
await_transform.As a workaround, we co_await a temporary QCoroSignal, which gcc seems
to correctly pass down as a lvalue reference, so no issues with copying.
Explictly
std::move()ingcoroSignaltoco_awaitwould also work,but it's weird.
I haven't confirmed whether this is a bug yet, as I first need to put
together a small reproducer case.