Introduce FieldParameterElement.

frog/leg/ssa/builder.dart

Index: frog/leg/ssa/builder.dart
diff --git a/frog/leg/ssa/builder.dart b/frog/leg/ssa/builder.dart
index bff34c72b9c5640db45444c9efd646e472c0e065..bd79bb89ca199480325affb71fe7667e7e7a6cfd 100644
--- a/frog/leg/ssa/builder.dart
+++ b/frog/leg/ssa/builder.dart
@@ -276,9 +276,15 @@ class LocalsHandler {
     params.forEachParameter((Element element) {
       HParameterValue parameter = new HParameterValue(element);
       builder.add(parameter);
-      // Note that for constructors [element] could be a field-element which we
-      // treat as if it was a local.
       directLocals[element] = parameter;
+      // If the [element] is a field-parameter (such as [:this.x:] then
+      // initialize the field element with its value.
+      // Note that in the constructor factory we treat fields as if they were
+      // locals.

[ngeoffray, 2012/03/15 10:06:01]

It looks like you should have an if/else here:
if (element.kind == PARAMETER) {
} else {
  // field parameter.
}

[floitsch, 2012/03/15 14:11:04]

Done.

+      if (element.kind == ElementKind.FIELD_PARAMETER) {
+        FieldParameterElement fieldParameterElement = element;
+        directLocals[fieldParameterElement.fieldElement] = parameter;
+      }
     });
     if (closureData.thisElement !== null) {
       // Once closures have been mapped to classes their instance members might
@@ -791,8 +797,14 @@ class SsaBuilder implements Visitor {
         int index = 0;
         FunctionParameters parameters =
             nextConstructor.computeParameters(compiler);
-        parameters.forEachParameter((parameter) {
-          localsHandler.updateLocal(parameter, arguments[index++]);
+        parameters.forEachParameter((Element parameter) {
+          HInstruction argument = arguments[index++];
+          localsHandler.updateLocal(parameter, argument);

[ngeoffray, 2012/03/15 10:06:01]

ditto for the if/else. The field parameter element should not be referenced.

[floitsch, 2012/03/15 14:11:04]

Done.

+          if (parameter.kind == ElementKind.FIELD_PARAMETER) {
+            FieldParameterElement fieldParameterElement = parameter;
+            localsHandler.updateLocal(fieldParameterElement.fieldElement,
+                                      argument);
+          }
         });
       } else {
         // A field initializer.
@@ -821,6 +833,10 @@ class SsaBuilder implements Visitor {
   HGraph buildFactory(ClassElement classElement,
                       FunctionElement functionElement) {
     FunctionExpression function = functionElement.parseNode(compiler);
+    // Note that constructors (like any other static function) do not need
+    // to deal with optional arguments. It is the callers job to provide all
+    // arguments as if they were positional.
+
     // The initializer list could contain closures.
     openFunction(functionElement, function);