Embed variable within macro

Question

I'm working with Rust and Rocket. At some point I can create a catcher to capture errors with:

#[catch(403)]
pub fn default_catcher() -> String {
  return String::from("something interesting");
}

As you can imagine the macro #[catch(403)] is capturing errors 403. Would it be possible to pass a constant to the macro? Something like:

const STATUS_CUSTOM_AUTHENTICATION_ERROR: u16 = 403;

#[catch(`${STATUS_CUSTOM_AUTHENTICATION_ERROR}`)]
...

Answer 1

Not with the macro.

If you want, you can write the boilerplate manually (please don't). The name of the static is important (it's how Rocket finds it):

// This is your function.
pub fn default_catcher() -> String {
    String::from("something interesting")
}

pub fn rocket_catch_fn_default_catcher(req: &rocket::Request) -> rocket::Result<'_> {
    let response = rocket::Responder::respond_to(default_catcher(), req)?;
    rocket::Response::build()
        .status(rocket::http::Status::new(
            STATUS_CUSTOM_AUTHENTICATION_ERROR,
            "some reason (e.g. `Forbidden` for 403)",
        ))
        .merge(response)
        .ok()
}
#[allow(non_upper_case_globals)]
pub static static_rocket_catch_info_for_default_catcher: rocket::StaticCatchInfo =
    rocket::StaticCatchInfo {
        code: 403u16,
        handler: rocket_catch_fn_default_catcher,
    };

Keep in mind that these are implementation details and can change at any moment.