fix: generate simple {} schema for tools with no parameters (#425)

Author: DaleSeo

crates/rmcp-macros/src/tool.rs

@@ -186,9 +186,9 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
                 rmcp::handler::server::common::cached_schema_for_type::<#params_ty>()
             })?
         } else {
-            // if not found, use the default EmptyObject schema
+            // if not found, use a simple empty JSON object
             syn::parse2::<Expr>(quote! {
-                rmcp::handler::server::common::cached_schema_for_type::<rmcp::model::EmptyObject>()
+                std::sync::Arc::new(serde_json::Map::new())
             })?
         }
     };

crates/rmcp/tests/test_tool_macros.rs

@@ -110,7 +110,7 @@ async fn test_tool_macros() {
 async fn test_tool_macros_with_empty_param() {
     let _attr = Server::empty_param_tool_attr();
     println!("{_attr:?}");
-    assert_eq!(_attr.input_schema.get("type").unwrap(), "object");
+    assert!(_attr.input_schema.get("type").is_none());
     assert!(_attr.input_schema.get("properties").is_none());
 }