Axum in combination with serde

This was one that bit me recently. I am using axum to develop my backend for a project I a developing. It takes json input from a post request and automatically deserializes it to a desired struct. However, I was getting this bizarre error message that took me a good amount of time to figure out. It turns out I just forgot to derive Deserialize on the struct. Extremely unintuitive.

use std::net::SocketAddr;
use axum::{Router, response::IntoResponse, routing::post, Json};
use serde::Deserialize;

#[tokio::main]
async fn main() {
    let app = Router::new()
        .route("/test", post(test));

    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}

// #[derive(Deserialize)] Without this the error is caused
struct Test {}

async fn test(
    Json(_): Json<Test>
) {}

The resulting error is:

error[E0277]: the trait bound `fn(Json<Test>) -> impl Future<Output = impl IntoResponse> {test}: Handler<_, _>` is not satisfied
   --> src/main.rs:9:30
    |
9   |         .route("/test", post(test));
    |                         ---- ^^^^ the trait `Handler<_, _>` is not implemented for `fn(Json<Test>) -> impl Future<Output = impl IntoResponse> {test}`
    |                         |
    |                         required by a bound introduced by this call
    |
    = help: the trait `Handler<T, ReqBody>` is implemented for `Layered<S, T>`
note: required by a bound in `post`
   --> /home/ford/.cargo/registry/src/github.com-1ecc6299db9ec823/axum-0.5.11/src/routing/method_routing.rs:400:1
    |
400 | top_level_handler_fn!(post, POST);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `post`
    = note: this error originates in the macro `top_level_handler_fn` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0277`.
warning: `atest` (bin "atest") generated 1 warning
error: could not compile `atest` due to previous error; 1 warning emitted

weiznich / rust-foundation-community-grant

Axum in combination with serde #2