Automatically generate Candid from Rust on the IC

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Update July 22nd, 2023: There is now a better way to automatically generate Candid from Rust. Check out my new blog post about that subject!

The ability to auto-generate the Candid declaration from Rust code on the Internet Computer is expected to become available in the second quarter of 2023.

In the meantime, a workaround can be used to generate these types, which I notably use in my open-source Blockchain-as-a-Service project, Juno.

Here’s how you can implement the workaround yourself.

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1. Annotate

Because this solution involves a workaround, the first step is to annotate the public methods that need to be exported to Candid types.

To do this, use the candid_method macro of the Candid crate, specifying the export type and, if necessary, the query type. The default is update.

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

#[candid_method(query)]
#[query]
fn hello(name: String) -> String {…