Use HasToJson when set Reponse/Notification parameters.

pkg/analysis_server/lib/src/protocol.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library protocol;
 
 import 'dart:collection';
 import 'dart:convert' show JsonDecoder;
 
+import 'package:analysis_server/src/collections.dart';
+
 /**
  * An abstract enumeration.
  */
 abstract class Enum2<E extends Enum2> implements Comparable<E> {
   /**
    * The name of this enum constant, as declared in the enum declaration.
    */
   final String name;
 
   /**
@@ skipping 589 matching lines @@
    * Return the value of the result field with the given [name].
    */
   Object getResult(String name) {
     return result[name];
   }
 
   /**
    * Set the value of the result field with the given [name] to the given [value].
    */
   void setResult(String name, Object value) {
-    result[name] = value;
+    result[name] = _toJson(value);
   }
 
   /**
    * Return a table representing the structure of the Json object that will be
    * sent to the client to represent this response.
    */
   Map<String, Object> toJson() {
     Map<String, Object> jsonObject = new HashMap<String, Object>();
     jsonObject[ID] = id;
     if (error != null) {
@@ skipping 233 matching lines @@
   /**
    * Return the value of the parameter with the given [name], or `null` if there
    * is no such parameter associated with this notification.
    */
   Object getParameter(String name) => params[name];
 
   /**
    * Set the value of the parameter with the given [name] to the given [value].
    */
   void setParameter(String name, Object value) {
-    params[name] = value;
+    params[name] = _toJson(value);
   }
 
   /**
    * Return a table representing the structure of the Json object that will be
    * sent to the client to represent this response.
    */
   Map<String, Object> toJson() {
     Map<String, Object> jsonObject = new HashMap<String, Object>();
     jsonObject[EVENT] = event;
     if (!params.isEmpty) {
@@ skipping 26 matching lines @@
   /**
    * The response to be returned as a result of the failure.
    */
   final Response response;
 
   /**
    * Initialize a newly created exception to return the given reponse.
    */
   RequestFailure(this.response);
 }
+
+/**
+ * Returns a JSON presention of [value].
+ */
+_toJson(Object value) {
+  if (value is HasToJson) {
+    return value.toJson();
+  }
+  if (value is Iterable) {
+    return value.map((item) => _toJson(item)).toList();
+  }
+  return value;
+}