Using export_service in project.did file

Hi there,
I would like to use the export_service macro, as defined in my rust library, which I compile to my WASM module.

use candid::export_service;

#[ic_cdk_macros::query(name = "__get_candid_interface_tmp_hack")]
fn export_candid() -> String {

Now what do I set into my project.did file?

I have tried setting

service :{
"export_candid": () -> (text) query;

but that seems to not work, as the canister method cannot be deployed called:

The Replica returned an error: code 3, message: "IC0302: Canister r7inp-6aaaa-aaaaa-aaabq-cai has no query method 'export_candid'"

Any suggestions? Thanks in advance!

This thread provides examples of export_service: