In the analysis server API, change RequestError.code to an enum.

pkg/analysis_server/lib/src/generated_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.
 //
 // This file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analysis_server/spec/generate_files".
 
 part of protocol;
 /**
@@ skipping 5649 matching lines @@
   @override
   String toString() => "ElementKind.$name";
 
   String toJson() => name;
 }
 
 /**
  * Error
  *
  * {
- *   "code": String
+ *   "code": RequestErrorCode
  *   "message": String
  *   "data": optional object
  * }
  */
 class Error {
   /**
    * A code that uniquely identifies the error that occurred.
    */
-  String code;
+  RequestErrorCode code;
 
   /**
    * A short description of the error.
    */
   String message;
 
   /**
    * Additional data related to the error. This field is omitted if there is no
    * additional data available.
    */
   Object data;
 
   Error(this.code, this.message, {this.data});
 
   factory Error.fromJson(JsonDecoder jsonDecoder, String jsonPath, Object json) {
     if (json == null) {
       json = {};
     }
     if (json is Map) {
-      String code;
+      RequestErrorCode code;
       if (json.containsKey("code")) {
-        code = jsonDecoder._decodeString(jsonPath + ".code", json["code"]);
+        code = new RequestErrorCode.fromJson(jsonDecoder, jsonPath + ".code", json["code"]);
       } else {
         throw jsonDecoder.missingKey(jsonPath, "code");
       }
       String message;
       if (json.containsKey("message")) {
         message = jsonDecoder._decodeString(jsonPath + ".message", json["message"]);
       } else {
         throw jsonDecoder.missingKey(jsonPath, "message");
       }
       Object data;
       if (json.containsKey("data")) {
         data = json["data"];
       }
       return new Error(code, message, data: data);
     } else {
       throw jsonDecoder.mismatch(jsonPath, "Error");
     }
   }
 
   Map<String, dynamic> toJson() {
     Map<String, dynamic> result = {};
-    result["code"] = code;
+    result["code"] = code.toJson();
     result["message"] = message;
     if (data != null) {
       result["data"] = data;
     }
     return result;
   }
 
   @override
   String toString() => JSON.encode(toJson());
 
@@ skipping 2341 matching lines @@
 
   @override
   int get hashCode {
     int hash = 0;
     hash = _JenkinsSmiHash.combine(hash, 114870849);
     return _JenkinsSmiHash.finish(hash);
   }
 }
 
 /**
+ * RequestErrorCode
+ *
+ * enum {
+ *   GET_ERRORS_ERROR
+ *   INVALID_PARAMETER
+ *   INVALID_REQUEST
+ *   SERVER_ALREADY_STARTED
+ *   UNANALYZED_PRIORITY_FILES
+ *   UNKNOWN_REQUEST
+ *   UNSUPPORTED_FEATURE
+ * }
+ */
+class RequestErrorCode {
+  /**
+   * An error occurred during the processing of an "analysis.getErrors"
+   * request.
+   */
+  static const GET_ERRORS_ERROR = const RequestErrorCode._("GET_ERRORS_ERROR");
+
+  /**
+   * One of the method parameters was invalid.
+   */
+  static const INVALID_PARAMETER = const RequestErrorCode._("INVALID_PARAMETER");
+
+  /**
+   * A malformed request was received.
+   */
+  static const INVALID_REQUEST = const RequestErrorCode._("INVALID_REQUEST");
+
+  /**
+   * The analysis server has already been started (and hence won't accept new
+   * connections).
+   */
+  static const SERVER_ALREADY_STARTED = const RequestErrorCode._("SERVER_ALREADY_STARTED");
+
+  /**
+   * An "analysis.setPriorityFiles" request includes one or more files that are
+   * not being analyzed.
+   */
+  static const UNANALYZED_PRIORITY_FILES = const RequestErrorCode._("UNANALYZED_PRIORITY_FILES");
+
+  /**
+   * A request was received which the analysis server does not recognize, or
+   * cannot handle in its current configuation.
+   */
+  static const UNKNOWN_REQUEST = const RequestErrorCode._("UNKNOWN_REQUEST");
+
+  /**
+   * The analysis server was requested to perform an action which is not
+   * supported.
+   */
+  static const UNSUPPORTED_FEATURE = const RequestErrorCode._("UNSUPPORTED_FEATURE");
+
+  final String name;
+
+  const RequestErrorCode._(this.name);
+
+  factory RequestErrorCode(String name) {
+    switch (name) {
+      case "GET_ERRORS_ERROR":
+        return GET_ERRORS_ERROR;
+      case "INVALID_PARAMETER":
+        return INVALID_PARAMETER;
+      case "INVALID_REQUEST":
+        return INVALID_REQUEST;
+      case "SERVER_ALREADY_STARTED":
+        return SERVER_ALREADY_STARTED;
+      case "UNANALYZED_PRIORITY_FILES":
+        return UNANALYZED_PRIORITY_FILES;
+      case "UNKNOWN_REQUEST":
+        return UNKNOWN_REQUEST;
+      case "UNSUPPORTED_FEATURE":
+        return UNSUPPORTED_FEATURE;
+    }
+    throw new Exception('Illegal enum value: $name');
+  }
+
+  factory RequestErrorCode.fromJson(JsonDecoder jsonDecoder, String jsonPath, Object json) {
+    if (json is String) {
+      try {
+        return new RequestErrorCode(json);
+      } catch(_) {
+        // Fall through
+      }
+    }
+    throw jsonDecoder.mismatch(jsonPath, "RequestErrorCode");
+  }
+
+  @override
+  String toString() => "RequestErrorCode.$name";
+
+  String toJson() => name;
+}
+
+/**
  * SearchResult
  *
  * {
  *   "location": Location
  *   "kind": SearchResultKind
  *   "isPotential": bool
  *   "path": List<Element>
  * }
  */
 class SearchResult {
@@ skipping 1585 matching lines @@
     return false;
   }
 
   @override
   int get hashCode {
     int hash = 0;
     hash = _JenkinsSmiHash.combine(hash, newName.hashCode);
     return _JenkinsSmiHash.finish(hash);
   }
 }