[RFC] Lifetime bound check for parameters of coroutines

Clang Frontend
19

Hi Utkarsh,
I also tested another footgun, namely lambda-captures with a coroutine lambda. Your analysis does not yet detect the buggy pattern below:

        int z = 10;

        auto k = [z]() -> co_future<int> {
            using namespace std::chrono_literals;
            co_await seastar::sleep(1s);
            co_return z;
        }();

        auto z_is_garbage = co_await std::move(k);

Here, the lambda object (including its captures) is already dead after the first co_await, so the capture z will be garbage when it is returned.

One possible fix is to store the lambda itself in the coroutine frame (before invoking)

        int z = 10;

        auto lamb = [z]() -> co_future<int> {
            using namespace std::chrono_literals;
            co_await seastar::sleep(1s);
            co_return z;
        };

        auto k = lamb();

        auto equal_to_z = co_await std::move(k);

Would you see any way to extend your lifetime analysis so that it can detect this footgun pattern with coroutine-lambdas ?