Produce error when duplicate field initializers are found

lib/compiler/implementation/resolver.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 TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   Type getType(TypeAnnotation annotation);
 }
 
@@ skipping 110 matching lines @@
       if (isConstructor) {
         resolveConstructorImplementation(element, tree);
       }
       ResolverVisitor visitor = new ResolverVisitor(compiler, element);
       visitor.useElement(tree, element);
       visitor.setupFunction(tree, element);
 
       if (isConstructor) {
         // Even if there is no initializer list we still have to do the
         // resolution in case there is an implicit super constructor call.
-        InitializerResolver resolver = new InitializerResolver(visitor);
+        InitializerResolver resolver =
+            new InitializerResolver(compiler, visitor);
         FunctionElement redirection =
             resolver.resolveInitializers(element, tree);
         if (redirection !== null) {
           resolveRedirectingConstructor(resolver, tree, element, redirection);
         }
       } else if (tree.initializers != null) {
         error(tree, MessageKind.FUNCTION_WITH_INITIALIZER);
       }
       visitBody(visitor, tree.body);
 
@@ skipping 257 matching lines @@
                             element);
   }
 
   error(Node node, MessageKind kind, [arguments = const []]) {
     ResolutionError message = new ResolutionError(kind, arguments);
     compiler.reportError(node, message);
   }
 }
 
 class InitializerResolver {
+  final Compiler compiler;

[ahe, 2012/08/15 10:47:07]

Don't need this field.

   final ResolverVisitor visitor;
   final Map<SourceString, Node> initialized;
   Link<Node> initializers;
   bool hasSuper;
 
-  InitializerResolver(this.visitor)
+  InitializerResolver(this.compiler, this.visitor)
     : initialized = new Map<SourceString, Node>(), hasSuper = false;
 
   error(Node node, MessageKind kind, [arguments = const []]) {
     visitor.error(node, kind, arguments);
   }
 
   warning(Node node, MessageKind kind, [arguments = const []]) {
     visitor.warning(node, kind, arguments);
   }
 
@@ skipping 120 matching lines @@
     }
     return null;
   }
 
   /**
    * Resolve all initializers of this constructor. In the case of a redirecting
    * constructor, the resolved constructor's function element is returned.
    */
   FunctionElement resolveInitializers(FunctionElement constructor,
                                       FunctionExpression functionNode) {
+     // keep track of all "this.param" parameters specified for constructor so

[ahe, 2012/08/15 10:47:07]

Not a proper sentence. By which I mean: please capitalize the first word, and
terminate the sentence with a period :-)

+     // that we can ensure that fields are initialized only once
+     FunctionSignature functionParameters =
+         constructor.computeSignature(compiler);

[ahe, 2012/08/15 10:47:07]

You can get this from visitor.compiler.

+     if (functionParameters != null) {
+       functionParameters.forEachParameter((Element element) {
+         if (element.kind == ElementKind.FIELD_PARAMETER) {
+           initialized[element.name] = element;
+         }
+       });
+     }
+
     if (functionNode.initializers === null) {
       initializers = const EmptyLink<Node>();
     } else {
       initializers = functionNode.initializers.nodes;
     }
     FunctionElement result;
     bool resolvedSuper = false;
     for (Link<Node> link = initializers;
          !link.isEmpty();
          link = link.tail) {
@@ skipping 1893 matching lines @@
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) {
     return library.find(name);
   }
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
   String toString() => '$element';
 }