fix(macros): accept const paths and concat! in tool/prompt descriptions

crates/rmcp-macros/src/prompt.rs

@@ -1,5 +1,5 @@
 use darling::{FromMeta, ast::NestedMeta};
-use proc_macro2::{Span, TokenStream};
+use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
 use syn::{Expr, Ident, ImplItemFn, ReturnType};
 
@@ -12,8 +12,10 @@ pub struct PromptAttribute {
     pub name: Option<String>,
     /// Human readable title of prompt
     pub title: Option<String>,
-    /// Optional description of what the prompt does
-    pub description: Option<String>,
+    /// Optional description of what the prompt does. A string literal, an
+    /// expression that evaluates to a `&'static str` (such as a `const` path
+    /// or `concat!`), or a `#[doc]` attribute on the function.
+    pub description: Option<darling::util::PreservedStrExpr>,
     /// Arguments that can be passed to the prompt
     pub arguments: Option<Expr>,
     /// Optional icons for the prompt
@@ -104,11 +106,8 @@ pub fn prompt(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream>
     };
 
     let name = attribute.name.unwrap_or_else(|| fn_ident.to_string());
-    let description = if let Some(s) = attribute.description {
-        Some(Expr::Lit(syn::ExprLit {
-            attrs: Vec::new(),
-            lit: syn::Lit::Str(syn::LitStr::new(&s, Span::call_site())),
-        }))
+    let description = if let Some(description) = attribute.description {
+        Some(description.into())
     } else {
         fn_item.attrs.iter().try_fold(None, extract_doc_line)?
     };

crates/rmcp-macros/src/tool.rs

@@ -1,7 +1,7 @@
 use darling::{FromMeta, ast::NestedMeta};
-use proc_macro2::{Span, TokenStream};
+use proc_macro2::TokenStream;
 use quote::{ToTokens, format_ident, quote};
-use syn::{Expr, Ident, ImplItemFn, LitStr, ReturnType, parse_quote};
+use syn::{Expr, Ident, ImplItemFn, ReturnType, parse_quote};
 
 use crate::common::extract_doc_line;
 
@@ -65,7 +65,10 @@ pub struct ToolAttribute {
     pub name: Option<String>,
     /// Human readable title of tool
     pub title: Option<String>,
-    pub description: Option<String>,
+    /// The description of the tool. A string literal, an expression that
+    /// evaluates to a `&'static str` (such as a `const` path or `concat!`),
+    /// or a `#[doc]` attribute on the function.
+    pub description: Option<darling::util::PreservedStrExpr>,
     /// A JSON Schema object defining the expected parameters for the tool
     pub input_schema: Option<Expr>,
     /// An optional JSON Schema object defining the structure of the tool's output
@@ -255,13 +258,9 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
         }
     });
 
-    let description_expr = if let Some(s) = attribute.description {
-        Some(Expr::Lit(syn::ExprLit {
-            attrs: Vec::new(),
-            lit: syn::Lit::Str(LitStr::new(&s, Span::call_site())),
-        }))
-    } else {
-        fn_item.attrs.iter().try_fold(None, extract_doc_line)?
+    let description_expr = match attribute.description {
+        Some(description) => Some(description.into()),
+        None => fn_item.attrs.iter().try_fold(None, extract_doc_line)?,
     };
     let resolved_tool_attr = ResolvedToolAttribute {
         name: attribute.name.unwrap_or_else(|| fn_ident.to_string()),

crates/rmcp/tests/test_prompt_macros.rs

@@ -73,8 +73,15 @@ impl Server {
             "This is a prompt with no parameters.".to_string(),
         )]
     }
+
+    #[prompt(description = CONST_PROMPT_DESCRIPTION)]
+    async fn const_description_prompt(&self) -> Vec<PromptMessage> {
+        vec![]
+    }
 }
 
+const CONST_PROMPT_DESCRIPTION: &str = "Prompt description from a const";
+
 // define generic service trait
 pub trait DataService: Send + Sync + 'static {
     fn get_context(&self) -> String;
@@ -155,6 +162,16 @@ async fn test_prompt_macros_with_empty_param() {
     );
 }
 
+#[test]
+fn test_prompt_description_accepts_const_expr() {
+    // tests https://github.com/modelcontextprotocol/rust-sdk/issues/1175
+    let prompt = Server::const_description_prompt_prompt_attr();
+    assert_eq!(
+        prompt.description.as_deref(),
+        Some(CONST_PROMPT_DESCRIPTION)
+    );
+}
+
 #[tokio::test]
 async fn test_prompt_macros_with_generics() {
     let mock_service = MockDataService;

crates/rmcp/tests/test_tool_macros.rs

@@ -61,6 +61,24 @@ impl Server {
 
     #[tool]
     async fn empty_param(&self) {}
+
+    #[tool(description = CONST_TOOL_DESCRIPTION)]
+    async fn const_description_tool(&self) {}
+
+    #[tool(description = concat!("part-a-", "part-b"))]
+    async fn concat_description_tool(&self) {}
+}
+
+const CONST_TOOL_DESCRIPTION: &str = "Description from a const";
+
+#[test]
+fn test_description_accepts_const_and_concat_exprs() {
+    // tests https://github.com/modelcontextprotocol/rust-sdk/issues/1175
+    let tool = Server::const_description_tool_tool_attr();
+    assert_eq!(tool.description.as_deref(), Some(CONST_TOOL_DESCRIPTION));
+
+    let tool = Server::concat_description_tool_tool_attr();
+    assert_eq!(tool.description.as_deref(), Some("part-a-part-b"));
 }
 
 /// Generic service trait.