Gets cannot find `__req` & '__data' in this scope errors

rkt-macro-test

#![feature(proc_macro_hygiene, decl_macro)]

#[macro_use]
extern crate rocket;

macro_rules! index {
    ($type:ty) => {
        #[get("/")]
        fn index(thing: rocket::State<$type>) -> String {
            format!("Thing: {}", *thing)
        }
    }
}

index!(i32);

fn main() {
    rocket::ignite().manage::<i32>(42).mount("/", routes![index]).launch();
}