fix: use cfg-gated Send+Sync supertraits to avoid semver break (#757)

crates/rmcp/src/handler/server.rs

@@ -4,8 +4,7 @@ use crate::{
     error::ErrorData as McpError,
     model::{TaskSupport, *},
     service::{
-        MaybeSend, MaybeSendFuture, NotificationContext, RequestContext, RoleServer, Service,
+        MaybeSendFuture, NotificationContext, RequestContext, RoleServer, Service, ServiceRole,
-        ServiceRole,
     },
 };
 
@@ -161,12 +160,8 @@ impl<H: ServerHandler> Service<RoleServer> for H {
     }
 }
 
-#[allow(unused_variables)]
+macro_rules! server_handler_methods {
-#[allow(
+    () => {
-    private_bounds,
-    reason = "MaybeSend is a sealed conditional Send + Sync alias"
-)]
-pub trait ServerHandler: Sized + MaybeSend + 'static {
         fn enqueue_task(
             &self,
             _request: CallToolRequestParams,
@@ -233,8 +228,9 @@ pub trait ServerHandler: Sized + MaybeSend + 'static {
             &self,
             request: Option<PaginatedRequestParams>,
             context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ListResourceTemplatesResult, McpError>> + MaybeSendFuture + '_
+        ) -> impl Future<Output = Result<ListResourceTemplatesResult, McpError>>
-    {
+               + MaybeSendFuture
+               + '_ {
             std::future::ready(Ok(ListResourceTemplatesResult::default()))
         }
         fn read_resource(
@@ -258,7 +254,9 @@ pub trait ServerHandler: Sized + MaybeSend + 'static {
             request: UnsubscribeRequestParams,
             context: RequestContext<RoleServer>,
         ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
-        std::future::ready(Err(McpError::method_not_found::<UnsubscribeRequestMethod>()))
+            std::future::ready(Err(
+                McpError::method_not_found::<UnsubscribeRequestMethod>(),
+            ))
         }
         fn call_tool(
             &self,
@@ -369,6 +367,19 @@ pub trait ServerHandler: Sized + MaybeSend + 'static {
             let _ = (request, context);
             std::future::ready(Err(McpError::method_not_found::<CancelTaskMethod>()))
         }
+    };
+}
+
+#[allow(unused_variables)]
+#[cfg(not(feature = "local"))]
+pub trait ServerHandler: Sized + Send + Sync + 'static {
+    server_handler_methods!();
+}
+
+#[allow(unused_variables)]
+#[cfg(feature = "local")]
+pub trait ServerHandler: Sized + 'static {
+    server_handler_methods!();
 }
 
 macro_rules! impl_server_handler_for_wrapper {

crates/rmcp/src/service.rs

@@ -128,11 +128,23 @@ pub type RxJsonRpcMessage<R> = JsonRpcMessage<
     <R as ServiceRole>::PeerNot,
 >;
 
-#[allow(
+#[cfg(not(feature = "local"))]
-    private_bounds,
+pub trait Service<R: ServiceRole>: Send + Sync + 'static {
-    reason = "MaybeSend is a sealed conditional Send + Sync alias"
+    fn handle_request(
-)]
+        &self,
-pub trait Service<R: ServiceRole>: MaybeSend + 'static {
+        request: R::PeerReq,
+        context: RequestContext<R>,
+    ) -> impl Future<Output = Result<R::Resp, McpError>> + MaybeSendFuture + '_;
+    fn handle_notification(
+        &self,
+        notification: R::PeerNot,
+        context: NotificationContext<R>,
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_;
+    fn get_info(&self) -> R::Info;
+}
+
+#[cfg(feature = "local")]
+pub trait Service<R: ServiceRole>: 'static {
     fn handle_request(
         &self,
         request: R::PeerReq,
@@ -197,11 +209,23 @@ impl<R: ServiceRole> Service<R> for Box<dyn DynService<R>> {
     }
 }
 
-#[allow(
+#[cfg(not(feature = "local"))]
-    private_bounds,
+pub trait DynService<R: ServiceRole>: Send + Sync {
-    reason = "MaybeSend is a sealed conditional Send + Sync alias"
+    fn handle_request(
-)]
+        &self,
-pub trait DynService<R: ServiceRole>: MaybeSend {
+        request: R::PeerReq,
+        context: RequestContext<R>,
+    ) -> MaybeBoxFuture<'_, Result<R::Resp, McpError>>;
+    fn handle_notification(
+        &self,
+        notification: R::PeerNot,
+        context: NotificationContext<R>,
+    ) -> MaybeBoxFuture<'_, Result<(), McpError>>;
+    fn get_info(&self) -> R::Info;
+}
+
+#[cfg(feature = "local")]
+pub trait DynService<R: ServiceRole> {
     fn handle_request(
         &self,
         request: R::PeerReq,