Only rewrite async closure for rust version before 1.85.0 (#3831)

* use_prepared_state with unit type is unlikely usage

---------

Co-authored-by: Matt "Siyuan" Yan <mattsy1999@gmail.com>

Author: Madoshakalaka

packages/yew-macro/Cargo.toml

@@ -22,10 +22,10 @@ quote = "1"
 syn = { version = "2", features = ["full", "extra-traits", "visit-mut"] }
 once_cell = "1"
 prettyplease = "0.2"
+rustversion = "1"
 
 # testing
 [dev-dependencies]
-rustversion = "1"
 trybuild = "1"
 yew = { path = "../yew" }
 

packages/yew-macro/src/use_prepared_state.rs

@@ -58,8 +58,8 @@ impl Parse for PreparedState {
 }
 
 impl PreparedState {
-    // Async closure is not stable, so we rewrite it to closure + async block
-    #[cfg(not(nightly_yew))]
+    // Async closure was not stable, so we rewrite it to closure + async block
+    #[rustversion::before(1.85)]
     pub fn rewrite_to_closure_with_async_block(&self) -> ExprClosure {
         use proc_macro2::Span;
         use syn::parse_quote;
@@ -95,7 +95,7 @@ impl PreparedState {
         closure
     }
 
-    #[cfg(nightly_yew)]
+    #[rustversion::since(1.85)]
     pub fn rewrite_to_closure_with_async_block(&self) -> ExprClosure {
         self.closure.clone()
     }

packages/yew/src/functional/hooks/use_prepared_state/mod.rs

@@ -47,7 +47,7 @@ pub use feat_ssr::*;
 /// # { todo!() }
 /// ```
 ///
-/// The first argument can also be an [async closure](https://github.com/rust-lang/rust/issues/62290).
+/// The first argument can also be an async closure
 ///
 /// `let state = use_prepared_state!(async |deps| -> ReturnType { ... }, deps)?;`
 ///
@@ -85,10 +85,6 @@ pub use feat_ssr::*;
 /// You MUST denote the return type of the closure with `|deps| -> ReturnType { ... }`. This
 /// type is used during client side rendering to deserialize the state prepared on the server
 /// side.
-///
-/// Whilst async closure is an unstable feature, the procedural macro will rewrite this to a
-/// closure that returns an async block automatically. You can use this hook with async closure
-/// in stable Rust.
 pub use use_prepared_state_macro as use_prepared_state;
 // With SSR.
 #[doc(hidden)]

tools/benchmark-ssr/src/main.rs

@@ -141,8 +141,9 @@ async fn bench_concurrent_task() -> Duration {
 
     #[function_component]
     fn Comp() -> HtmlResult {
-        let _state = use_prepared_state!((), async move |_| -> () {
+        let _state = use_prepared_state!((), async move |_| -> usize {
             sleep(Duration::from_secs(1)).await;
+            42
         })?;
 
         Ok(Html::default())