You can always pass the async executor to the sync code and spawn async coroutines into it. And you can keep it in a global context as well to avoid parameters.

You can always pass the async executor to the sync code and spawn async coroutines into it. And you can keep it in a global context as well to avoid parameters. E.g. there is `Handle::current()` for exactly this purpose in Tokio. Function coloring is just a theoretical disadvantage - people like to bring it up in discussions, but it almost never matters in practice, and it is even not universally considered a bad thing. I actually like to see in the signature if a function I'm calling into can suspend for an arbitrary amount of time.