[Bug c++/124729] New: [coroutines] await-expressions are split in a brace-init-list

[ddvamp007 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124729

            Bug ID: 124729
           Summary: [coroutines] await-expressions are split in a
                    brace-init-list
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ddvamp007 at gmail dot com
  Target Milestone: ---

https://godbolt.org/z/465n8bx93

When a brace-init-list for array initialization contains await-expressions, its
evaluation is effectively split into two phases: the await-ready and
await-suspend parts of all await-expressions are evaluated first, followed by
the evaluation of the initializers.

#include <coroutine>
#include <iostream>

struct Tag {
  struct promise_type {
    Tag get_return_object() { return {}; }
    std::suspend_never initial_suspend() { return {}; }
    std::suspend_never final_suspend() noexcept { return {}; }
    void return_void() {}
    void unhandled_exception() {}
  };
};

struct S {
  S() { std::cout << " S" << std::endl; }
  ~S() { std::cout << "~S" << std::endl; }
};

struct Awaiter {
  auto await_ready() {
    std::cout << "ready" << std::endl;
    return false;
  }
  auto await_suspend(auto) {
    std::cout << "suspend" << std::endl;
    return false;
  }
  auto await_resume() {
    std::cout << "resume" << std::endl;
    return S{};
  }
};

auto make() {
  std::cout << "make" << std::endl;
  return S{};
}

Tag Coroutine() {
  S arr[] = {co_await Awaiter{},
             make(),
             co_await Awaiter{}};
}

int main() {
  Coroutine();
}

--std=c++2c -O0 -pedantic -Wall -Wextra

Output:
ready
suspend
ready
suspend
resume
 S
make
 S
resume
 S
~S
~S
~S