The header <coroutine> defines the primary template coroutine_traits
such that if ArgTypes is a parameter pack of types and if the
qualified-id R::promise_type is valid and denotes a type, then
coroutine_traits<R,ArgTypes...> has the following publicly accessible
member:
using promise_type = typename R::promise_type;
this should not prevent more specialised cases and the following
code should be accepted, but is currently rejected with:
'error: coroutine return type ‘void’ is not a class'
This is because the check for non-class-ness of the return value was
in the wrong place; it needs to be carried out in a SFINAE context.
The following patch removes the restriction in the traits template
instantiation and allows for the case that the ramp function could
return void.
The <coroutine> header is amended to implement the required
functionality.
gcc/cp/ChangeLog:
2020-04-28 Iain Sandoe <iain@sandoe.co.uk>
PR c++/94759
* coroutines.cc (coro_promise_type_found_p): Do not
exclude non-classes here (this needs to be handled in the
coroutine header).
(morph_fn_to_coro): Allow for the case where the coroutine
returns void.
-f () /* { dg-error {'operator new' is provided by 'std::__n4861::coroutine_traits<coro1>::promise_type' \{aka 'coro1::promise_type'\} but is not usable with the function signature 'coro1 f\(\)'} } */
+f () /* { dg-error {'operator new' is provided by 'std::__n4861::__coroutine_traits_impl<coro1, void>::promise_type' \{aka 'coro1::promise_type'\} but is not usable with the function signature 'coro1 f\(\)'} } */
-f () /* { dg-error {'operator delete' is provided by 'std::__n4861::coroutine_traits<coro1>::promise_type' \{aka 'coro1::promise_type'\} but is not usable with the function signature 'coro1 f\(\)'} } */
+f () /* { dg-error {'operator delete' is provided by 'std::__n4861::__coroutine_traits_impl<coro1, void>::promise_type' \{aka 'coro1::promise_type'\} but is not usable with the function signature 'coro1 f\(\)'} } */
-f () /* { dg-error {'coro1::promise_type::get_return_object_on_allocation_failure\(\)\(\)' is provided by 'std::__n4861::coroutine_traits<coro1>::promise_type' \{aka 'coro1::promise_type'\} but 'operator new' is not marked 'throw\(\)' or 'noexcept'} } */
+f () /* { dg-error {'coro1::promise_type::get_return_object_on_allocation_failure\(\)\(\)' is provided by 'std::__n4861::__coroutine_traits_impl<coro1, void>::promise_type' \{aka 'coro1::promise_type'\} but 'operator new' is not marked 'throw\(\)' or 'noexcept'} } */