feat: support Axum extractors with state other than () (#1275)

This requires state to be provided via context using a special handler, but allows for extractors that use this state, rather than only `()`, as previously.

integrations/axum/src/lib.rs

@@ -1276,18 +1276,24 @@ impl ExtractorHelper {
         }
     }
 
-    pub async fn extract<F, T, U>(&self, f: F) -> Result<U, T::Rejection>
+    pub async fn extract<F, T, U, S>(
+        &self,
+        f: F,
+        s: S,
+    ) -> Result<U, T::Rejection>
     where
-        F: Extractor<T, U>,
-        T: std::fmt::Debug + Send + FromRequestParts<()> + 'static,
+        S: Sized,
+        F: Extractor<T, U, S>,
+        T: std::fmt::Debug + Send + FromRequestParts<S> + 'static,
         T::Rejection: std::fmt::Debug + Send + 'static,
     {
         let mut parts = self.parts.lock().await;
-        let data = T::from_request_parts(&mut parts, &()).await?;
+        let data = T::from_request_parts(&mut parts, &s).await?;
         Ok(f.call(data).await)
     }
 }
 
+/// Getting ExtractorHelper from a request will return an ExtractorHelper whose state is ().
 impl<B> From<Request<B>> for ExtractorHelper {
     fn from(req: Request<B>) -> Self {
         // TODO provide body for extractors there, too?
@@ -1324,34 +1330,71 @@ impl<B> From<Request<B>> for ExtractorHelper {
 #[tracing::instrument(level = "trace", fields(error), skip_all)]
 pub async fn extract<T, U>(
     cx: Scope,
-    f: impl Extractor<T, U>,
+    f: impl Extractor<T, U, ()>,
 ) -> Result<U, T::Rejection>
 where
     T: std::fmt::Debug + Send + FromRequestParts<()> + 'static,
     T::Rejection: std::fmt::Debug + Send + 'static,
+{
+    extract_with_state(cx, (), f).await
+}
+
+/// A helper to make it easier to use Axum extractors in server functions. This takes
+/// a handler function and state as its arguments. The handler rules similar to Axum
+/// [handlers](https://docs.rs/axum/latest/axum/extract/index.html#intro): it is an async function
+/// whose arguments are “extractors.”
+///
+/// ```rust,ignore
+/// #[server(QueryExtract, "/api")]
+/// pub async fn query_extract(cx: Scope) -> Result<String, ServerFnError> {
+///     use axum::{extract::Query, http::Method};
+///     use leptos_axum::extract;
+///     let state: ServerState = use_context::<crate::ServerState>(cx)
+///          .ok_or(ServerFnError::ServerError("No server state".to_string()))?;
+///
+///     extract_with_state(cx, state, |method: Method, res: Query<MyQuery>| async move {
+///             format!("{method:?} and {}", res.q)
+///         },
+///     )
+///     .await
+///     .map_err(|e| ServerFnError::ServerError("Could not extract method and query...".to_string()))
+/// }
+/// ```
+#[tracing::instrument(level = "trace", fields(error), skip_all)]
+pub async fn extract_with_state<T, U, S>(
+    cx: Scope,
+    state: S,
+    f: impl Extractor<T, U, S>,
+) -> Result<U, T::Rejection>
+where
+    S: Sized,
+    T: std::fmt::Debug + Send + FromRequestParts<S> + 'static,
+    T::Rejection: std::fmt::Debug + Send + 'static,
 {
     use_context::<ExtractorHelper>(cx)
         .expect(
             "should have had ExtractorHelper provided by the leptos_axum \
              integration",
         )
-        .extract(f)
+        .extract(f, state)
         .await
 }
 
-pub trait Extractor<T, U>
+pub trait Extractor<T, U, S>
 where
-    T: FromRequestParts<()>,
+    S: Sized,
+    T: FromRequestParts<S>,
 {
     fn call(self, args: T) -> Pin<Box<dyn Future<Output = U>>>;
 }
 
 macro_rules! factory_tuple ({ $($param:ident)* } => {
-    impl<Func, Fut, U, $($param,)*> Extractor<($($param,)*), U> for Func
+    impl<Func, Fut, U, S, $($param,)*> Extractor<($($param,)*), U, S> for Func
     where
-        $($param: FromRequestParts<()> + Send,)*
+        $($param: FromRequestParts<S> + Send,)*
         Func: FnOnce($($param),*) -> Fut + 'static,
         Fut: Future<Output = U> + 'static,
+        S: Sized + Send + Sync,
     {
         #[inline]
         #[allow(non_snake_case)]