Implementation of null-aware operators.

pkg/compiler/lib/src/tree/unparser.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.
 
 part of tree;
 
 String unparse(Node node, {minify: true}) {
   Unparser unparser = new Unparser(minify: minify);
   unparser.unparse(node);
   return unparser.result;
@@ skipping 408 matching lines @@
     visit(node.receiver);
     CascadeReceiver asCascadeReceiver = node.receiver.asCascadeReceiver();
     if (asCascadeReceiver != null) {
       newline();
       indentMore();
       indentMore();
       write(asCascadeReceiver.cascadeOperator.value);
       indentLess();
       indentLess();
     } else if (node.selector.asOperator() == null) {
-      write('.');
+      write(node.isConditional ? '?.' : '.');
     } else if (spacesNeeded) {
       write(' ');
     }
   }
 
   unparseSendArgument(Send node, {bool spacesNeeded: false}) {
     if (node.argumentsNode == null) return;
 
     if(node.isIsNotCheck) {
       Send argNode = node.arguments.head;
@@ skipping 412 matching lines @@
   }
 
   visitStatement(Statement node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitStringNode(StringNode node) {
     throw 'internal error'; // Should not be called.
   }
 }