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From: "lemourin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99575] New: [coroutines] unexpected move when co_awaiting a
 nonmoveable object
Date: Sat, 13 Mar 2021 13:37:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99575

            Bug ID: 99575
           Summary: [coroutines] unexpected move when co_awaiting a
                    nonmoveable object
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lemourin at gmail dot com
  Target Milestone: ---

```
#if __has_include(<coroutine>)
#include <coroutine>
namespace stdx {
using std::coroutine_handle;
using std::noop_coroutine;
using std::suspend_always;
using std::suspend_never;
}  // namespace stdx
#elif __has_include(<experimental/coroutine>)
#include <experimental/coroutine>
namespace stdx {
using std::experimental::coroutine_handle;
using std::experimental::noop_coroutine;
using std::experimental::suspend_always;
using std::experimental::suspend_never;
}  // namespace stdx
#else
#error "coroutines unsupported"
#endif

class Task {
 public:
  struct promise_type {
    Task get_return_object() { return Task{}; }
    stdx::suspend_always initial_suspend() { return {}; }
    stdx::suspend_always final_suspend() noexcept { return {}; }
    void unhandled_exception() {}
    void return_void() {}
  };

  bool await_ready() const { return false; }
  void await_suspend(stdx::coroutine_handle<void> continuation) {}
  void await_resume() {}
};

class NonMoveableTask {
 public:
  NonMoveableTask() =3D default;
  NonMoveableTask(const NonMoveableTask&) =3D delete;
  NonMoveableTask(NonMoveableTask&&) =3D delete;

  NonMoveableTask& operator=3D(const NonMoveableTask&) =3D delete;
  NonMoveableTask& operator=3D(NonMoveableTask&& other) =3D delete;

  bool await_ready() const { return false; }
  void await_suspend(stdx::coroutine_handle<void>) {}
  void await_resume() {}
};

Task Foo(NonMoveableTask* task) { co_await* task; }

int main() {}
```

The above code snippet does not compile with gcc with the following error l=
og:
`
move.cc: In function =E2=80=98Task Foo(NonMoveableTask*)=E2=80=99:
move.cc:50:45: error: use of deleted function
=E2=80=98NonMoveableTask::NonMoveableTask(NonMoveableTask&&)=E2=80=99
   50 | Task Foo(NonMoveableTask* task) { co_await* task; }
      |                                             ^~~~
move.cc:40:3: note: declared here
   40 |   NonMoveableTask(NonMoveableTask&&) =3D delete;
      |   ^~~~~~~~~~~~~~~
make: *** [<builtin>: move] Error 1
`

clang and msvc accept it. If the move constructor is available code compiled
with gcc uses it and leaves `task` in a moved from state.=