Error reporting on File in dart:io

runtime/bin/file.dart

 // Copyright (c) 2012, 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.
 
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
   static final READ = const FileMode(0);
@@ skipping 347 matching lines @@
 
   /**
    * Sets the handler that gets called when errors occur when
    * operating on this file.
    */
   void set onError(void handler(String error));
 }
 
 
 class FileIOException implements Exception {
-  const FileIOException([String this.message = ""]);
-  String toString() => "FileIOException: $message";
+  const FileIOException([String this.message = "",
+                         OSError this.osError = null]);
+  String toString() {
+    StringBuffer sb = new StringBuffer();
+    sb.add("FileIOException");
+    if (message != null) {
+      sb.add(": $message");
+      if (osError != null) {
+        sb.add(" (${osError.toString()})");
+      }
+    } else if (osError != null) {
+      sb.add(": ${osError.toString()}");
+    }
+    return sb.toString();
+  }
   final String message;
+  final OSError osError;
 }