middleware::from_fn() vs middleware::from_fn_with_state() is a bit misleading

[mqudsi]

Going by the names, one would be forgiven for thinking the difference between axum::middleware::from_fn() and axum::middleware::from_fn_with_state() is that one supports taking state (presumably at a performance cost?) and the other doesn't.

I learned the hard way that no extractor is supported, so even for handlers that don't need state but use any extractor (e.g. CookieJar), you need to call middleware::from_fn_with_state(state.clone(), ...), needlessly cloning the state you're not going to access (and don't even take as a parameter).

e.g. this doesn't compile:

    struct AppState;
    async fn takes_cookies(
        cookies: axum_extra::extract::SignedCookieJar,
        request: axum::extract::Request,
        next: axum::middleware::Next,
    ) -> Response {
        todo!();
    }
    let app = Router::new()
        .route_layer(axum::middleware::from_fn(takes_cookies))
        .with_state(AppState{});

but this will:

    struct AppState;
    async fn takes_cookies(
        cookies: axum_extra::extract::SignedCookieJar,
        request: axum::extract::Request,
        next: axum::middleware::Next,
    ) -> Response {
        todo!();
    }
    let app = Router::new()
        .route_layer(axum::middleware::from_fn_with_state(AppState{}, takes_cookies))
        .with_state(AppState{});

Is this intentional and is there perhaps a better name than from_fn_with_state() that conveys the actual difference?

What's the best way to avoid cloning the app state here (can't just use () as the app state because the generic bounds won't line up any longer)?

[jplatte]

from_fn certainly allows extractors, just not ones that rely on state like SignedCookieJar.