chore(transport): document and test Send async rustc bug

Signed-off-by: Roman Volosatovs <[email protected]>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "wrpc"
-version = "0.2.0"
+version = "0.2.1"
 description = "WebAssembly component-native RPC framework based on WIT"
 
 authors.workspace = true
@@ -109,6 +109,7 @@ quote = { version = "1", default-features = false }
 rcgen = { version = "0.13", default-features = false }
 reqwest = { version = "0.11", default-features = false }
 rustls = { version = "0.23", default-features = false }
+send-future = { version = "0.1", default-features = false }
 serde = { version = "1", default-features = false }
 serde_json = { version = "1", default-features = false }
 syn = { version = "2", default-features = false, features = ["printing"] }

crates/transport/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "wrpc-transport"
-version = "0.26.1"
+version = "0.26.2"
 description = "wRPC core transport functionality"
 
 authors.workspace = true
@@ -24,6 +24,7 @@ tokio = { workspace = true, features = ["macros", "rt"] }
 tokio-stream = { workspace = true }
 tokio-util = { workspace = true, features = ["codec", "io"] }
 tracing = { workspace = true, features = ["attributes"] }
+send-future = { workspace = true }
 wasm-tokio = { workspace = true, features = ["tracing"] }
 
 [dev-dependencies]

crates/transport/src/lib.rs

@@ -7,6 +7,7 @@ mod value;
 
 #[cfg(feature = "frame")]
 pub use frame::{Decoder as FrameDecoder, Encoder as FrameEncoder, FrameRef};
+pub use send_future::SendFuture;
 pub use value::*;
 
 use core::future::Future;
@@ -48,6 +49,45 @@ pub trait Invoke: Send + Sync + 'static {
     type Incoming: AsyncRead + Index<Self::Incoming> + Send + Sync + Unpin + 'static;
 
     /// Invoke function `func` on instance `instance`
+    ///
+    /// Note, that compilation of code calling methods on [`Invoke`] implementations within [`Send`] async functions
+    /// may fail with hard-to-debug errors due to a compiler bug:
+    /// [https://github.com/rust-lang/rust/issues/96865](https://github.com/rust-lang/rust/issues/96865)
+    ///
+    /// The following fails to compile with rustc 1.78.0:
+    ///
+    /// ```compile_fail
+    /// use core::future::Future;
+    ///
+    /// fn invoke_send<T>() -> impl Future<Output = anyhow::Result<(T::Outgoing, T::Incoming)>> + Send
+    /// where
+    ///     T: wrpc_transport::Invoke<Context = ()> + Default,
+    /// {
+    ///     async { T::default().invoke((), "compiler-bug", "free", "since".into(), [[Some(2024)].as_slice(); 0]).await }
+    /// }
+    /// ```
+    ///
+    /// ```text
+    /// async { T::default().invoke((), "compiler-bug", "free", "since".into(), [[Some(2024)].as_slice(); 0]).await }
+    /// |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `AsRef` is not general enough
+    ///  |
+    ///  = note: `[&'0 [Option<usize>]; 0]` must implement `AsRef<[&'1 [Option<usize>]]>`, for any two lifetimes `'0` and `'1`...
+    ///  = note: ...but it actually implements `AsRef<[&[Option<usize>]]>`
+    /// ```
+    ///
+    /// The fix is to call [`send`](SendFuture::send) provided by [`send_future::SendFuture`], re-exported by this crate, on the future before awaiting:
+    /// ```
+    /// use core::future::Future;
+    /// use wrpc_transport::SendFuture as _;
+    ///
+    /// fn invoke_send<T>() -> impl Future<Output = anyhow::Result<(T::Outgoing, T::Incoming)>> + Send
+    /// where
+    ///     T: wrpc_transport::Invoke<Context = ()> + Default,
+    /// {
+    ///     async { T::default().invoke((), "compiler-bug", "free", "since".into(), [[Some(2024)].as_slice(); 0]).send().await }
+    /// }
+    /// ```
+
     fn invoke<P>(
         &self,
         cx: Self::Context,
@@ -325,6 +365,36 @@ mod tests {
 
     use super::*;
 
+    fn invoke_values_send<T>() -> impl Future<
+        Output = anyhow::Result<(
+            Pin<
+                Box<
+                    dyn Stream<Item = Vec<Pin<Box<dyn Future<Output = String> + Send + Sync>>>>
+                        + Send
+                        + Sync,
+                >,
+            >,
+        )>,
+    > + Send
+    where
+        T: Invoke<Context = ()> + Default,
+    {
+        async {
+            let wrpc = T::default();
+            let ((r0,), _) = wrpc
+                .invoke_values(
+                    (),
+                    "wrpc-test:integration/async",
+                    "with-streams",
+                    (),
+                    [[None].as_slice()],
+                )
+                .send()
+                .await?;
+            Ok(r0)
+        }
+    }
+
     async fn call_invoke<T: Invoke>(
         i: &T,
         cx: T::Context,
@@ -333,7 +403,7 @@ mod tests {
         i.invoke(cx, "foo", "bar", Bytes::default(), &paths).await
     }
 
-    pub async fn call_invoke_async<T>(
+    async fn call_invoke_async<T>(
     ) -> anyhow::Result<(Pin<Box<dyn Stream<Item = Bytes> + Send + Sync>>,)>
     where
         T: Invoke<Context = ()> + Default,