Suppose I have two coroutines, coroutine_a and coroutine_b. In coroutine_a it calls:

co_await awaiter_a;

The awaiter_a::await_suspend returns a coroutine handler of coroutine_b. As a result, coroutine_b is resumed. Then, in coroutine_b, it calls:

co_await awaiter_b;

The awaiter_b::await_suspend returns void. As a result, control should be returned to its caller/resumer coroutine_a. What will happen when control is returned to coroutine_a?

I think there are two options:

1. coroutine_a returns to its caller.
2. coroutine_a stays suspended until someone resumes it.

Which one is correct? Or is it something else?