state always need to implement Clone

Fix #2821

Author: yanns

axum/src/extract/state.rs

@@ -22,7 +22,7 @@ use std::{
 /// // here you can put configuration, database connection pools, or whatever
 /// // state you need
 /// //
-/// // see "When states need to implement `Clone`" for more details on why we need
+/// // see "Why states need to implement `Clone`" for more details on why we need
 /// // `#[derive(Clone)]` here.
 /// #[derive(Clone)]
 /// struct AppState {}
@@ -247,14 +247,14 @@ use std::{
 /// }
 /// ```
 ///
-/// # When states need to implement `Clone`
+/// # Why states need to implement `Clone`
 ///
 /// Your top level state type must implement `Clone` to be extractable with `State`:
 ///
 /// ```
 /// use axum::extract::State;
 ///
-/// // no substates, so to extract to `State<AppState>` we must implement `Clone` for `AppState`
+/// // to extract to `State<AppState>` we must implement `Clone` for `AppState`
 /// #[derive(Clone)]
 /// struct AppState {}
 ///
@@ -265,32 +265,6 @@ use std::{
 ///
 /// This works because of [`impl<S> FromRef<S> for S where S: Clone`][`FromRef`].
 ///
-/// This is also true if you're extracting substates, unless you _never_ extract the top level
-/// state itself:
-///
-/// ```
-/// use axum::extract::{State, FromRef};
-///
-/// // we never extract `State<AppState>`, just `State<InnerState>`. So `AppState` doesn't need to
-/// // implement `Clone`
-/// struct AppState {
-///     inner: InnerState,
-/// }
-///
-/// #[derive(Clone)]
-/// struct InnerState {}
-///
-/// impl FromRef<AppState> for InnerState {
-///     fn from_ref(app_state: &AppState) -> InnerState {
-///         app_state.inner.clone()
-///     }
-/// }
-///
-/// async fn api_users(State(inner): State<InnerState>) {
-///     // ...
-/// }
-/// ```
-///
 /// In general however we recommend you implement `Clone` for all your state types to avoid
 /// potential type errors.
 ///