Responder trait derivation for actix-web

[zizhengtai]

I'm experimenting with askama and actix-web, and noticed the Responder trait derivation sometimes doesn't work. Here is an example project:

Cargo.toml:

[package]
name = "try-askama"
version = "0.1.0"
authors = ["Z"]
edition = "2018"

[dependencies]
actix-web = "0.7"
askama = { version = "0.7", features = ["with-actix-web"] }

src/main.rs:

use actix_web::{App, HttpRequest};
use askama::Template;

#[derive(Template)]
#[template(ext = "html", source = "Hello, {{ name }}!")]
struct HelloTemplate {
    name: &'static str,
}

fn index(_: &HttpRequest) -> HelloTemplate {  // <-- Compiles
// fn index(_: &HttpRequest) -> impl Template { // <-- DOESN'T compile
    HelloTemplate { name: "John" }
}

fn main() {
    App::new().resource("/", |r| r.get().f(index));
}

If I try to make the handler return impl Template (or anything like Result<impl Template>, Box<Future<impl Template, Error>>, etc.), I get this error:

error[E0277]: the trait bound `impl askama::Template: actix_web::handler::Responder` is not satisfied
  --> src/main.rs:15:42
   |
15 |     App::new().resource("/", |r| r.get().f(index));
   |                                          ^ the trait `actix_web::handler::Responder` is not implemented for `impl askama::Template`

[zzau13]

The correct type of return for this case is actix_web::Responder .

use actix_web::{App, HttpRequest, Responder};
use askama::Template;

#[derive(Template)]
#[template(ext = "html", source = "Hello, {{ name }}!")]
struct HelloTemplate {
    name: &'static str,
}


fn index(_: &HttpRequest) -> impl Responder { 
    HelloTemplate { name: "John" }
}

fn main() {
    App::new().resource("/", |r| r.get().f(index));
}

As you can see in the documentation, the correct trait for generate responses for clients is Responder.

@djc Can close it?

[djc]

@botika good call! @zizhengtai does that work for you?

[zizhengtai]

Thanks @botika @djc, this should work for me.