mcp: introduce options for AddTool

mcp/server.go

@@ -239,7 +239,7 @@ func (s *Server) AddTool(t *Tool, h ToolHandler) {
 		func() bool { s.tools.add(st); return true })
 }
 
-func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*Tool, ToolHandler, error) {
+func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out], schemaOpts *jsonschema.ForOptions) (*Tool, ToolHandler, error) {
 	tt := *t
 
 	// Special handling for an "any" input: treat as an empty object.
@@ -248,7 +248,7 @@ func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*Tool, ToolHan
 	}
 
 	var inputResolved *jsonschema.Resolved
-	if _, err := setSchema[In](&tt.InputSchema, &inputResolved); err != nil {
+	if _, err := setSchema[In](&tt.InputSchema, &inputResolved, schemaOpts); err != nil {
 		return nil, nil, fmt.Errorf("input schema: %w", err)
 	}
 
@@ -263,7 +263,7 @@ func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*Tool, ToolHan
 	)
 	if t.OutputSchema != nil || reflect.TypeFor[Out]() != reflect.TypeFor[any]() {
 		var err error
-		elemZero, err = setSchema[Out](&tt.OutputSchema, &outputResolved)
+		elemZero, err = setSchema[Out](&tt.OutputSchema, &outputResolved, schemaOpts)
 		if err != nil {
 			return nil, nil, fmt.Errorf("output schema: %v", err)
 		}
@@ -366,16 +366,15 @@ func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*Tool, ToolHan
 //
 // TODO(rfindley): we really shouldn't ever return 'null' results. Maybe we
 // should have a jsonschema.Zero(schema) helper?
-func setSchema[T any](sfield *any, rfield **jsonschema.Resolved) (zero any, err error) {
+func setSchema[T any](sfield *any, rfield **jsonschema.Resolved, schemaOpts *jsonschema.ForOptions) (zero any, err error) {
 	var internalSchema *jsonschema.Schema
 	if *sfield == nil {
 		rt := reflect.TypeFor[T]()
 		if rt.Kind() == reflect.Pointer {
 			rt = rt.Elem()
 			zero = reflect.Zero(rt).Interface()
 		}
-		// TODO: we should be able to pass nil opts here.
-		internalSchema, err = jsonschema.ForType(rt, &jsonschema.ForOptions{})
+		internalSchema, err = jsonschema.ForType(rt, schemaOpts)
 		if err == nil {
 			*sfield = internalSchema
 		}
@@ -389,6 +388,20 @@ func setSchema[T any](sfield *any, rfield **jsonschema.Resolved) (zero any, err
 	return zero, err
 }
 
+// AddToolOption is an option for the AddTool function.
+type AddToolOption func(*addToolOptions)
+
+type addToolOptions struct {
+	schemaOpts *jsonschema.ForOptions
+}
+
+// WithSchemaOptions returns an AddToolOption that sets options for schema inference.
+func WithSchemaOptions(opts *jsonschema.ForOptions) AddToolOption {
+	return func(ato *addToolOptions) {
+		ato.schemaOpts = opts
+	}
+}
+
 // AddTool adds a tool and typed tool handler to the server.
 //
 // If the tool's input schema is nil, it is set to the schema inferred from the
@@ -408,8 +421,14 @@ func setSchema[T any](sfield *any, rfield **jsonschema.Resolved) (zero any, err
 // Unlike [Server.AddTool], AddTool does a lot automatically, and forces
 // tools to conform to the MCP spec. See [ToolHandlerFor] for a detailed
 // description of this automatic behavior.
-func AddTool[In, Out any](s *Server, t *Tool, h ToolHandlerFor[In, Out]) {
-	tt, hh, err := toolForErr(t, h)
+func AddTool[In, Out any](s *Server, t *Tool, h ToolHandlerFor[In, Out], opts ...AddToolOption) {
+	o := addToolOptions{
+		schemaOpts: &jsonschema.ForOptions{},
+	}
+	for _, opt := range opts {
+		opt(&o)
+	}
+	tt, hh, err := toolForErr(t, h, o.schemaOpts)
 	if err != nil {
 		panic(fmt.Sprintf("AddTool: tool %q: %v", t.Name, err))
 	}

mcp/server_test.go

@@ -562,7 +562,7 @@ func testToolForSchema[In, Out any](t *testing.T, tool *Tool, in string, out Out
 	th := func(context.Context, *CallToolRequest, In) (*CallToolResult, Out, error) {
 		return nil, out, nil
 	}
-	gott, goth, err := toolForErr(tool, th)
+	gott, goth, err := toolForErr(tool, th, &jsonschema.ForOptions{})
 	if err != nil {
 		t.Fatal(err)
 	}