I’d go further and say it’s not possible to fully implement async/await without compiler help.
I got really far with stateful, back in 2016 [1]. Stateful was an attempt to write a coroutine library in a proc macro, which generated state machines, as opposed to using os primitives like green threading. This was back before the rust community really started working in this space. I ended up extracting the type system from rustc to do much of the analysis, but it ultimately failed due to how difficult it was to output rust code that respected the borrow checker rules. I also didn’t have anything like the pinning system, so I couldn’t catch move issues either.
It was a much better idea to just implement this in the compiler.
I got really far with stateful, back in 2016 [1]. Stateful was an attempt to write a coroutine library in a proc macro, which generated state machines, as opposed to using os primitives like green threading. This was back before the rust community really started working in this space. I ended up extracting the type system from rustc to do much of the analysis, but it ultimately failed due to how difficult it was to output rust code that respected the borrow checker rules. I also didn’t have anything like the pinning system, so I couldn’t catch move issues either.
It was a much better idea to just implement this in the compiler.
[1]: http://erickt.github.io/blog/2016/01/27/stateful-in-progress...