Produce error when duplicate field initializers are found

lib/compiler/implementation/resolver.dart

Index: lib/compiler/implementation/resolver.dart
diff --git a/lib/compiler/implementation/resolver.dart b/lib/compiler/implementation/resolver.dart
index aff2ad7514ac706518559708544f85e8f670c237..913abdb0432ead0f285ad3b0e53de659b21f2959 100644
--- a/lib/compiler/implementation/resolver.dart
+++ b/lib/compiler/implementation/resolver.dart
@@ -128,7 +128,8 @@ class ResolverTask extends CompilerTask {
       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) {
@@ -406,12 +407,13 @@ class ResolverTask extends CompilerTask {
 }
 
 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 []]) {
@@ -552,6 +554,18 @@ class InitializerResolver {
    */
   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 {