Parse rhs of select! arms using match-arm rules

futures-macro/Cargo.toml

@@ -18,7 +18,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0.60"
 quote = "1.0"
-syn = { version = "2.0.8", features = ["full"] }
+syn = { version = "2.0.52", features = ["full"] }
 
 [lints]
 workspace = true

futures-macro/src/select.rs

@@ -59,7 +59,7 @@ impl Parse for Select {
 
             // `=> <expr>`
             input.parse::<Token![=>]>()?;
-            let expr = input.parse::<Expr>()?;
+            let expr = Expr::parse_with_earlier_boundary_rule(input)?;
 
             // Commas after the expression are only optional if it's a `Block`
             // or it is the last branch in the `match`.
@@ -229,7 +229,7 @@ fn select_inner(input: TokenStream, random: bool) -> TokenStream {
     let branches = parsed.normal_fut_handlers.into_iter().zip(variant_names.iter()).map(
         |((pat, expr), variant_name)| {
             quote! {
-                #enum_ident::#variant_name(#pat) => { #expr },
+                #enum_ident::#variant_name(#pat) => #expr,
             }
         },
     );

futures/tests/async_await_macros.rs

@@ -57,6 +57,18 @@ fn select() {
     assert!(ran);
 }
 
+#[test]
+fn select_grammar() {
+    // Parsing after `=>` using Expr::parse would parse `{}() = future::ready(())`
+    // as one expression.
+    block_on(async {
+        select! {
+            () = future::pending::<()>() => {}
+            () = future::ready(()) => {}
+        }
+    });
+}
+
 #[test]
 fn select_biased() {
     let (tx1, rx1) = oneshot::channel::<i32>();