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From: "victor.burckel at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/101243] New: Coroutine lambda capture is destroyed twice
Date: Mon, 28 Jun 2021 13:37:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101243

            Bug ID: 101243
           Summary: Coroutine lambda capture is destroyed twice
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: victor.burckel at gmail dot com
  Target Milestone: ---

In a corourtine expecting a std::function<void()> parameter, passing a
temporary lambda with a capture results in the capture being destroyed twic=
e:
See it on gldbolt, gcc vs clang outputs
https://godbolt.org/z/jx9Yh5cqM

#include <fmt/core.h>

#include <coroutine>
#include <functional>

#ifdef __clang__
namespace std::experimental {
using std::coroutine_handle;
using std::coroutine_traits;
}  // namespace std::experimental
#endif

struct task {
  struct promise_type;
  using handle_type =3D std::coroutine_handle<promise_type>;

  struct promise_type {
    auto initial_suspend() noexcept { return std::suspend_always{}; }
    auto final_suspend() noexcept { return std::suspend_always{}; }
    void return_void() noexcept {}
    task get_return_object() noexcept {
      return task{handle_type::from_promise(*this)};
    }
    void unhandled_exception() noexcept {}
  };

  task(handle_type h) : h{h} {}
  ~task() {
    if (h) {
      fmt::print("destroying coroutine\n");
      h.destroy();
      fmt::print("coroutine destroyed\n");
    }
  }

  bool await_ready() const noexcept { return false; }
  bool await_suspend(std::coroutine_handle<>) noexcept {
    h.resume();
    return true;
  }
  void await_resume() noexcept {}

  void resume() { h.resume(); }

  handle_type h;
};

struct S {
  S() { fmt::print("S::S()\n"); }
  S(const S&) { fmt::print("S::S(const S&)\n"); }
  S(S&&) { fmt::print("S::S(S&&)\n"); }
  ~S() { fmt::print("S::~S()\n"); }
};

task g(std::function<void()>) {
  fmt::print("in g()\n");
  co_return;
}

task f() {
  fmt::print("calling g()\n");
  co_await g([s=3DS{}] {});
  fmt::print("g called\n");
}

int main() {
  auto task =3D f();
  fmt::print("resuming f\n");
  task.resume();
  fmt::print("resuming f\n");
  task.resume();
}

Gcc outputs:
resuming f
calling g()
S::S()
S::S(S&&)
in g()
resuming f
destroying coroutine
S::~S()
coroutine destroyed
S::~S()
S::~S()
g called
destroying coroutine
coroutine destroyed

While clang outputs:
resuming f
calling g()
S::S()
S::S(S&&)
in g()
resuming f
destroying coroutine
S::~S()
coroutine destroyed
S::~S()
g called
destroying coroutine
coroutine destroyed=