Namely, await isn't a matter of just inserting some compiler-defined behavior at a specific point. It requires rewriting the control flow of the surrounding function. The await! macro did this by invoking a magical unstable keyword `yield`, but even that still has to be done within the current function (e.g. the implementation of await! must be a macro, not a function).
I mean, that just means the compiler needs to ignore the `Future::await()` function scope and rewrite the context above. It's already being magical. A slight indirection in implementation would be worth the pedagogical clarity, I think.
Namely, await isn't a matter of just inserting some compiler-defined behavior at a specific point. It requires rewriting the control flow of the surrounding function. The await! macro did this by invoking a magical unstable keyword `yield`, but even that still has to be done within the current function (e.g. the implementation of await! must be a macro, not a function).