Rocket & async with regular main()

I decided to give Rocket on the master branch a test, and was pleasantly surprised that async:ifying our Rocket test app was very easy. However, there's just one thing that I'm unclear on -- how does one go about manually initializing everything in a regular fn main() (rather than use the [#launch] fn rocket() -> rocket::Rocket.

... or more generically; given a project that uses proc macros, how can one inspect the resulting output?

If they don't mention it on the documentation, you can use cargo expand to see the code generated by the macro.