Generator local scope resources are not cleaned up after coroutine object going out of scope

[SidneyCogdill]

I would have expected the local scope resources within a generator coroutine to be cleaned up at coroutine object destruction, but it didn't.

cobalt::generator<int> gg()
{
    boost::scope::defer_guard release = [&] { std::println("exiting gg"); };

    co_yield 10;
    co_yield 11;
    co_return 12;
}

cobalt::task<void> t12()
{
    {
        auto gen = gg();
        co_await gen;
    } // <- `gen` out of scope here, `release` should be destructed but it doesn't.
    std::println("gen is out of scope");
}

cobalt::main co_main(int, char **)
{
    {
        co_await t12();
    }
    std::println("t12 is out of scope");
    co_return 0;
}

Expected order:

exiting gg
gen is out of scope
t12 is out of scope

Actual order:

gen is out of scope
t12 is out of scope
exiting gg

This is very surprising (considering that co_await-ing does have proper cancellation support that cleans up the local scope objects) and it has caused a nasty bug that took me hours to diagnose.