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From: "fchelnokov at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/103963] New: Coroutine return type must not be copy- or
 move-constructible
Date: Mon, 10 Jan 2022 14:44:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103963

            Bug ID: 103963
           Summary: Coroutine return type must not be copy- or
                    move-constructible
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

This is a valid program:
```
#include <coroutine>

class task {
public:
    class task_promise {
    public:
        task get_return_object() { return
task{handle_type::from_promise(*this)}; }
        auto initial_suspend() { return std::suspend_always{}; }
        auto final_suspend() noexcept { return std::suspend_never{}; }
        void return_void() {}
        void unhandled_exception() {}
    };
    using handle_type =3D std::coroutine_handle<task_promise>;
    handle_type handle;

    auto await_ready() { return false; }
    auto await_suspend(handle_type) { return handle; }
    void await_resume() { handle.resume(); }

    using promise_type =3D task_promise;
    task(handle_type h) : handle(h) {}
    task(const task&) =3D delete;
    task& operator=3D(const task&) =3D delete;
    task(task&&) =3D delete;
    task& operator=3D(task&&) =3D delete;
};

int main() {
    task f =3D []() -> task { co_return; }();
    task g =3D [&f]() -> task { co_await f; }();
    g.handle.resume();
}
```

The code is accepted in MSVC, but not in GCC.

GCC 11.2 complains on the missing move-constructor:
error: use of deleted function 'task::task(task&&)'

and GCC trunk - on the missing copy-constructor:
error: use of deleted function 'task::task(const task&)'

Demo: https://gcc.godbolt.org/z/1c7fajqn8

Related discussion: https://stackoverflow.com/q/70641924/7325599=