Implement override checks.

dart/lib/compiler/implementation/tree/nodes.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.
 
 interface Visitor<R> {
   R visitBlock(Block node);
   R visitBreakStatement(BreakStatement node);
   R visitCascade(Cascade node);
   R visitCascadeReceiver(CascadeReceiver node);
   R visitCaseMatch(CaseMatch node);
@@ skipping 1057 matching lines @@
   /** Bit pattern to easy check what modifiers are present. */
   final int flags;
 
   static final int FLAG_STATIC = 1;
   static final int FLAG_ABSTRACT = FLAG_STATIC << 1;
   static final int FLAG_FINAL = FLAG_ABSTRACT << 1;
   static final int FLAG_VAR = FLAG_FINAL << 1;
   static final int FLAG_CONST = FLAG_VAR << 1;
   static final int FLAG_FACTORY = FLAG_CONST << 1;
 
-  Modifiers(NodeList nodes)
-    : this.nodes = nodes, flags = computeFlags(nodes.nodes);
+  Modifiers(NodeList nodes) : this.withFlags(nodes, computeFlags(nodes.nodes));
 
   Modifiers.empty() : this(new NodeList.empty());
 
+  Modifiers.withFlags(this.nodes, this.flags);
+
   static int computeFlags(Link<Node> nodes) {
     int flags = 0;
     for (; !nodes.isEmpty(); nodes = nodes.tail) {
       String value = nodes.head.asIdentifier().source.stringValue;
       if (value === 'static') flags += FLAG_STATIC;
       else if (value === 'abstract') flags += FLAG_ABSTRACT;
       else if (value === 'final') flags += FLAG_FINAL;
       else if (value === 'var') flags += FLAG_VAR;
       else if (value === 'const') flags += FLAG_CONST;
       else if (value === 'factory') flags += FLAG_FACTORY;
       else throw 'internal error: ${nodes.head}';
     }
     return flags;
   }
 
   Modifiers asModifiers() => this;
   Token getBeginToken() => nodes.getBeginToken();
   Token getEndToken() => nodes.getEndToken();
   accept(Visitor visitor) => visitor.visitModifiers(this);
   visitChildren(Visitor visitor) => nodes.accept(visitor);
 
   bool isStatic() => (flags & FLAG_STATIC) != 0;
   bool isAbstract() => (flags & FLAG_ABSTRACT) != 0;
   bool isFinal() => (flags & FLAG_FINAL) != 0;
   bool isVar() => (flags & FLAG_VAR) != 0;
   bool isConst() => (flags & FLAG_CONST) != 0;
   bool isFactory() => (flags & FLAG_FACTORY) != 0;
+
+  String toString() {
+    LinkBuilder<String> builder = new LinkBuilder<String>();
+    if (isStatic()) builder.addLast('static');
+    if (isAbstract()) builder.addLast('abstract');
+    if (isFinal()) builder.addLast('final');
+    if (isVar()) builder.addLast('var');
+    if (isConst()) builder.addLast('const');
+    if (isFactory()) builder.addLast('factory');
+    StringBuffer buffer = new StringBuffer();
+    builder.toLink().printOn(buffer, ', ');
+    return buffer.toString();
+  }
 }
 
 class StringInterpolation extends StringNode {
   final LiteralString string;
   final NodeList parts;
 
   StringInterpolation(this.string, this.parts);
 
   StringInterpolation asStringInterpolation() => this;
 
@@ skipping 586 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send !== null) return f(send.arguments.head);
 }