Automatic Candid Generation in Rust: Exploring the ic_cdk v0.10.0 Update

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So, yesterday I upgraded Juno to the latest release of ic_cdk and discovered that the automatic generation of the Candid declarations needed an update. In this post, I will walk you through the process of migrating your project.

Update: On September 18th, 2023, a new version of the ic_cdk v0.11.0 has been released, and this article has been updated accordingly.

Previous Workaround

If you have previously relied on automatic type generation, chances are you used the export_service crate and the workaround involving generating and writing the did files to the file system through a test by running cargo test .

I covered this approach in a previous blog post earlier this year, but to summarize, your code most probably looked like the following:

use ic_cdk_macros::{query, update};
use ic_cdk::export::candid::{candid_method};
use ic_cdk::export::candid::{export_service};

// Your code
​
#[candid_method(query)]
#[query]
fn hello(name: String) -> String {
    format!("Hello, {}!", name)
}
​
#[candid_method(update)]
#[update]
fn world(name: String) -> String {
    format!("World, {}!", name)
}

// The workaround to generate did files automatically

fn export_candid() -> String {
    export_service!()…