fix(model): deprecate ServerInfo and ClientInfo aliases (#1156)

* fix(model): deprecate ServerInfo and ClientInfo aliases

Those names collide with the protocol's serverInfo/clientInfo fields,
which are only Implementation identity. Prefer InitializeResult and
InitializeRequestParams. Handler trait signatures, the tool_handler
macro output, tests, examples and docs now use the canonical types; the
aliases remain as deprecated shims for the rest of 3.x.

Fixes #1082

* fix(model): keep public signatures on the deprecated aliases

The public API check compares rendered signatures, and rustdoc records a
type alias by the name it was written with. Respelling
`ServerHandler::get_info`, `ClientHandler::get_info`,
`DiscoverResult::from_server_info` and `impl ClientHandler for ClientInfo`
onto `InitializeResult`/`InitializeRequestParams` therefore reads as
changed public items even though the aliases resolve to those exact types
and nothing downstream breaks.

Put those four signatures back on the aliases so the published API is
byte-identical, and note why at the alias definitions. The deprecation
still steers new code, and the macro output, tests, examples and docs
keep using the canonical names.

* fix(model): migrate leftover ClientInfo test sites

Two tests landed on main after the alias deprecation and still named
ClientInfo. Clippy -D warnings and the no-local feature test job both
failed on them.

Author: teddytennant

README.md

@@ -99,10 +99,10 @@ Use [`ClientServiceExt::serve_with_lifecycle`](crates/rmcp/src/service/client.rs
 select another lifecycle explicitly:
 
 ```rust, ignore
-use rmcp::{ClientInfo, ClientLifecycleMode, ClientServiceExt, ProtocolVersion};
+use rmcp::{ClientLifecycleMode, ClientServiceExt, InitializeRequestParams, ProtocolVersion};
 
 // Start directly with server/discover and include client metadata on every request.
-let client = ClientInfo::default()
+let client = InitializeRequestParams::default()
     .serve_with_lifecycle(
         transport,
         ClientLifecycleMode::Discover {
@@ -113,7 +113,7 @@ let client = ClientInfo::default()
 
 // Or probe the discover lifecycle and fall back when a legacy server reports
 // that server/discover is not implemented or does not respond within 10 seconds.
-let client = ClientInfo::default()
+let client = InitializeRequestParams::default()
     .serve_with_lifecycle(
         transport,
         ClientLifecycleMode::Auto {
@@ -369,8 +369,8 @@ use serde_json::json;
 struct MyServer;
 
 impl ServerHandler for MyServer {
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(
+    fn get_info(&self) -> InitializeResult {
+        InitializeResult::new(
             ServerCapabilities::builder()
                 .enable_resources()
                 .build(),
@@ -582,8 +582,8 @@ impl MyServer {
 
 #[prompt_handler]
 impl ServerHandler for MyServer {
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(ServerCapabilities::builder().enable_prompts().build())
+    fn get_info(&self) -> InitializeResult {
+        InitializeResult::new(ServerCapabilities::builder().enable_prompts().build())
     }
 }
 ```
@@ -934,8 +934,8 @@ Enable the logging capability, handle level changes from the client, and send lo
 use rmcp::{ServerHandler, model::*, service::RequestContext};
 
 impl ServerHandler for MyServer {
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(
+    fn get_info(&self) -> InitializeResult {
+        InitializeResult::new(
             ServerCapabilities::builder()
                 .enable_logging()
                 .build(),
@@ -1007,8 +1007,8 @@ Enable the completions capability and implement the `complete()` handler. Use `r
 use rmcp::{ErrorData as McpError, ServerHandler, model::*, service::RequestContext, RoleServer};
 
 impl ServerHandler for MyServer {
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(
+    fn get_info(&self) -> InitializeResult {
+        InitializeResult::new(
             ServerCapabilities::builder()
                 .enable_completions()
                 .enable_prompts()
@@ -1253,8 +1253,8 @@ use rmcp::{
 };
 
 impl ServerHandler for MyServer {
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(
+    fn get_info(&self) -> InitializeResult {
+        InitializeResult::new(
             ServerCapabilities::builder()
                 .enable_tools()
                 .enable_tool_list_changed()
@@ -1584,7 +1584,7 @@ use rmcp::transport::StreamableHttpClientTransport;
 
 // Defaults are stateless-friendly.
 let transport = StreamableHttpClientTransport::from_uri("http://localhost:8000/mcp");
-let client = ClientInfo::default().serve(transport).await?;
+let client = InitializeRequestParams::default().serve(transport).await?;
 ```
 
 **Example:** [`examples/servers/src/counter_streamhttp.rs`](examples/servers/src/counter_streamhttp.rs) (server), [`examples/clients/src/streamable_http.rs`](examples/clients/src/streamable_http.rs) (client)
@@ -1638,7 +1638,7 @@ server example). The client transport connects with a single URI:
 use rmcp::transport::StreamableHttpClientTransport;
 
 let transport = StreamableHttpClientTransport::from_uri("http://localhost:8000/mcp");
-let client = ClientInfo::default().serve(transport).await?;
+let client = InitializeRequestParams::default().serve(transport).await?;
 ```
 
 The client allows up to 16 ordinary http POSTs at once. Configure this with
@@ -1742,10 +1742,10 @@ knows what the other supports. Declare yours with the `ServerCapabilities`
 builder in `get_info()`:
 
 ```rust,ignore
-use rmcp::model::{ServerCapabilities, ServerInfo};
+use rmcp::model::{InitializeResult, ServerCapabilities};
 
-fn get_info(&self) -> ServerInfo {
-    ServerInfo::new(
+fn get_info(&self) -> InitializeResult {
+    InitializeResult::new(
         ServerCapabilities::builder()
             .enable_tools()
             .enable_prompts()

conformance/src/bin/client.rs

@@ -74,8 +74,8 @@ impl ClientHandler for BasicClientHandler {}
 struct ElicitationDefaultsClientHandler;
 
 impl ClientHandler for ElicitationDefaultsClientHandler {
-    fn get_info(&self) -> ClientInfo {
-        let mut info = ClientInfo::default();
+    fn get_info(&self) -> InitializeRequestParams {
+        let mut info = InitializeRequestParams::default();
         info.capabilities.elicitation = Some(
             ElicitationCapability::new()
                 .with_form(FormElicitationCapability::new().with_schema_validation(true)),
@@ -163,8 +163,8 @@ impl ClientHandler for ElicitationDefaultsClientHandler {
 struct FullClientHandler;
 
 impl ClientHandler for FullClientHandler {
-    fn get_info(&self) -> ClientInfo {
-        let mut info = ClientInfo::default();
+    fn get_info(&self) -> InitializeRequestParams {
+        let mut info = InitializeRequestParams::default();
         info.capabilities.elicitation = Some(
             ElicitationCapability::new()
                 .with_form(FormElicitationCapability::new().with_schema_validation(true)),

conformance/src/bin/server.rs

@@ -704,8 +704,8 @@ impl ServerHandler for ConformanceServer {
         (name == "test_custom_header").then(custom_header_tool)
     }
 
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(
+    fn get_info(&self) -> InitializeResult {
+        InitializeResult::new(
             ServerCapabilities::builder()
                 .enable_prompts()
                 .enable_prompts_list_changed()

crates/rmcp-macros/src/lib.rs

@@ -217,8 +217,8 @@ pub fn tool_router(attr: TokenStream, input: TokenStream) -> TokenStream {
 /// ```rust,ignore
 /// #[tool_handler]
 /// impl ServerHandler for MyToolHandler {
-///     fn get_info(&self) -> ServerInfo {
-///         ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
+///     fn get_info(&self) -> InitializeResult {
+///         InitializeResult::new(ServerCapabilities::builder().enable_tools().build())
 ///     }
 /// }
 /// ```

crates/rmcp-macros/src/tool_handler.rs

@@ -116,7 +116,7 @@ pub(crate) enum CallerCapability {
     Prompts,
 }
 
-/// Build a `get_info()` method that returns `ServerInfo` with the appropriate capabilities.
+/// Build a `get_info()` method that returns `InitializeResult` with the appropriate capabilities.
 ///
 /// The caller declares its own capability via `caller`. Sibling handler attributes
 /// (`prompt_handler`, `tool_handler`) are detected automatically
@@ -157,8 +157,8 @@ pub(crate) fn build_get_info(
     }
 
     syn::parse2::<ImplItem>(quote! {
-        fn get_info(&self) -> rmcp::model::ServerInfo {
-            rmcp::model::ServerInfo::new(
+        fn get_info(&self) -> rmcp::model::InitializeResult {
+            rmcp::model::InitializeResult::new(
                 rmcp::model::ServerCapabilities::builder()
                     #(#capability_calls)*
                     .build()

crates/rmcp/src/handler/client.rs

@@ -275,7 +275,7 @@ macro_rules! client_handler_methods {
         }
 
         fn get_info(&self) -> ClientInfo {
-            ClientInfo::default()
+            InitializeRequestParams::default()
         }
     };
 }

crates/rmcp/src/handler/server.rs

@@ -601,7 +601,7 @@ macro_rules! server_handler_methods {
         }
 
         fn get_info(&self) -> ServerInfo {
-            ServerInfo::default()
+            InitializeResult::default()
         }
 
         /// SEP-2663 `tasks/get`: return the current [`DetailedTask`] state.

crates/rmcp/src/model.rs

@@ -1119,7 +1119,26 @@ impl InitializeResult {
     }
 }
 
+/// Full server initialize payload (`InitializeResult`).
+///
+/// Prefer [`InitializeResult`]. The name collides with the protocol's
+/// `serverInfo` field, which is only the [`Implementation`] identity (#1082).
+//
+// The signatures this crate publishes (`ServerHandler::get_info`,
+// `DiscoverResult::from_server_info`, and the `ClientInfo` equivalents below)
+// keep spelling the alias. It resolves to the same type, so the spelling makes
+// no difference to callers, but rustdoc records the name as written and the
+// public API check treats a respelling as a changed item. Moving those
+// signatures onto the canonical names is a documented API change and belongs in
+// the next major release.
+#[deprecated(note = "use `InitializeResult` instead")]
 pub type ServerInfo = InitializeResult;
+
+/// Full client initialize params (`InitializeRequestParams`).
+///
+/// Prefer [`InitializeRequestParams`]. The name collides with the protocol's
+/// `clientInfo` field, which is only the [`Implementation`] identity (#1082).
+#[deprecated(note = "use `InitializeRequestParams` instead")]
 pub type ClientInfo = InitializeRequestParams;
 
 /// Information negotiated about a server peer.
@@ -1284,7 +1303,7 @@ impl DiscoverResult {
         supported_versions: Vec<ProtocolVersion>,
         server_info: ServerInfo,
     ) -> Self {
-        let ServerInfo {
+        let InitializeResult {
             capabilities,
             server_info,
             instructions,
@@ -1332,9 +1351,9 @@ impl ServerPeerInfo {
 }
 
 #[allow(clippy::derivable_impls)]
-impl Default for ServerInfo {
+impl Default for InitializeResult {
     fn default() -> Self {
-        ServerInfo {
+        InitializeResult {
             protocol_version: ProtocolVersion::default(),
             capabilities: ServerCapabilities::default(),
             server_info: Implementation::from_build_env(),
@@ -1345,9 +1364,9 @@ impl Default for ServerInfo {
 }
 
 #[allow(clippy::derivable_impls)]
-impl Default for ClientInfo {
+impl Default for InitializeRequestParams {
     fn default() -> Self {
-        ClientInfo {
+        InitializeRequestParams {
             meta: None,
             protocol_version: ProtocolVersion::default(),
             capabilities: ClientCapabilities::default(),

crates/rmcp/src/service/client.rs

@@ -13,13 +13,13 @@ use crate::{
     model::{
         ArgumentInfo, CacheScope, CallToolRequest, CallToolRequestParams, CallToolResponse,
         CallToolResult, CancelTaskParams, CancelTaskRequest, CancelledNotification,
-        CancelledNotificationParam, ClientInfo, ClientJsonRpcMessage, ClientNotification,
-        ClientRequest, ClientResult, CompleteRequest, CompleteRequestParams, CompleteResult,
-        CompletionContext, CompletionInfo, DEFAULT_MRTR_MAX_ROUNDS, DiscoverRequest,
-        DiscoverRequestParams, DiscoverResult, ErrorData, GetExtensions, GetMeta, GetPromptRequest,
+        CancelledNotificationParam, ClientJsonRpcMessage, ClientNotification, ClientRequest,
+        ClientResult, CompleteRequest, CompleteRequestParams, CompleteResult, CompletionContext,
+        CompletionInfo, DEFAULT_MRTR_MAX_ROUNDS, DiscoverRequest, DiscoverRequestParams,
+        DiscoverResult, ErrorData, GetExtensions, GetMeta, GetPromptRequest,
         GetPromptRequestParams, GetPromptResponse, GetPromptResult, GetTaskParams, GetTaskRequest,
-        GetTaskResult, InitializeRequest, InitializedNotification, InputRequest,
-        InputRequiredResult, InputResponses, JsonRpcResponse, ListPromptsRequest,
+        GetTaskResult, InitializeRequest, InitializeRequestParams, InitializedNotification,
+        InputRequest, InputRequiredResult, InputResponses, JsonRpcResponse, ListPromptsRequest,
         ListPromptsResult, ListResourceTemplatesRequest, ListResourceTemplatesResult,
         ListResourcesRequest, ListResourcesResult, ListToolsRequest, ListToolsResult,
         NumberOrString, PaginatedRequestParams, ProgressNotification, ProgressNotificationParam,
@@ -266,7 +266,7 @@ impl ServiceRole for RoleClient {
     type PeerReq = ServerRequest;
     type PeerResp = ServerResult;
     type PeerNot = ServerNotification;
-    type Info = ClientInfo;
+    type Info = InitializeRequestParams;
     type PeerInfo = ServerPeerInfo;
     type InitializeError = ClientInitializeError;
     const IS_CLIENT: bool = true;
@@ -870,7 +870,7 @@ async fn legacy_startup<S, T>(
     transport: &mut T,
     id_provider: &Arc<AtomicU32RequestIdProvider>,
     peer: &Peer<RoleClient>,
-    client_info: ClientInfo,
+    client_info: InitializeRequestParams,
 ) -> Result<(), ClientInitializeError>
 where
     S: Service<RoleClient>,
@@ -919,7 +919,7 @@ async fn discover_startup<S, T>(
     transport: &mut T,
     id_provider: &Arc<AtomicU32RequestIdProvider>,
     peer: &Peer<RoleClient>,
-    client_info: &ClientInfo,
+    client_info: &InitializeRequestParams,
     preferred_versions: Vec<ProtocolVersion>,
 ) -> Result<DiscoverOutcome, ClientInitializeError>
 where

crates/rmcp/src/service/server.rs

@@ -13,14 +13,15 @@ use super::*;
 use crate::model::{ElicitRequest, ElicitRequestParams, ElicitResult, ElicitationAction};
 use crate::{
     model::{
-        CancelledNotification, CancelledNotificationParam, ClientInfo, ClientJsonRpcMessage,
+        CancelledNotification, CancelledNotificationParam, ClientJsonRpcMessage,
         ClientNotification, ClientRequest, ClientResult, CreateMessageRequest,
-        CreateMessageRequestParams, CreateMessageResult, EmptyResult, ErrorData, ListRootsRequest,
-        ListRootsResult, LoggingMessageNotification, LoggingMessageNotificationParam,
-        ProgressNotification, ProgressNotificationParam, PromptListChangedNotification,
-        ProtocolVersion, ResourceListChangedNotification, ResourceUpdatedNotification,
-        ResourceUpdatedNotificationParam, ServerInfo, ServerNotification, ServerRequest,
-        ServerResult, SubscriptionFilter, SubscriptionsAcknowledgedNotification,
+        CreateMessageRequestParams, CreateMessageResult, EmptyResult, ErrorData,
+        InitializeRequestParams, InitializeResult, ListRootsRequest, ListRootsResult,
+        LoggingMessageNotification, LoggingMessageNotificationParam, ProgressNotification,
+        ProgressNotificationParam, PromptListChangedNotification, ProtocolVersion,
+        ResourceListChangedNotification, ResourceUpdatedNotification,
+        ResourceUpdatedNotificationParam, ServerNotification, ServerRequest, ServerResult,
+        SubscriptionFilter, SubscriptionsAcknowledgedNotification,
         SubscriptionsAcknowledgedNotificationParams, ToolListChangedNotification,
     },
     transport::DynamicTransportError,
@@ -37,8 +38,8 @@ impl ServiceRole for RoleServer {
     type PeerReq = ClientRequest;
     type PeerResp = ClientResult;
     type PeerNot = ClientNotification;
-    type Info = ServerInfo;
-    type PeerInfo = ClientInfo;
+    type Info = InitializeResult;
+    type PeerInfo = InitializeRequestParams;
 
     type InitializeError = ServerInitializeError;
     const IS_CLIENT: bool = false;