Clone AST nodes of default formal parameters prior to constant evaluation.

pkg/analyzer/lib/src/generated/constant.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.constant;
 
 import 'dart:collection';
@@ skipping 1130 matching lines @@
       // No evaluation needs to be done; constructor declarations are only in
       // the dependency graph to ensure that any constants referred to in
       // initializer lists and parameter defaults are evaluated before
       // invocations of the constructor.  However we do need to annotate the
       // element as being free of constant evaluation cycles so that later code
       // will know that it is safe to evaluate.
       ConstructorElementImpl constructor = constNode.element;
       constructor.isCycleFree = true;
     } else if (constNode is FormalParameter) {
       if (constNode is DefaultFormalParameter) {
-        DefaultFormalParameter parameter = constNode;
-        ParameterElement element = parameter.element;
-        Expression defaultValue = parameter.defaultValue;
+        ParameterElement element = constNode.element;
+        Expression defaultValue =
+            (element as PotentiallyConstVariableElement).constantInitializer;
         if (defaultValue != null) {
           RecordingErrorListener errorListener = new RecordingErrorListener();
           ErrorReporter errorReporter =
               new ErrorReporter(errorListener, element.source);
           DartObjectImpl dartObject = defaultValue
               .accept(new ConstantVisitor(evaluationEngine, errorReporter));
           (element as ParameterElementImpl).evaluationResult =
               new EvaluationResultImpl.con2(dartObject, errorListener.errors);
         }
       }
@@ skipping 4030 matching lines @@
       return BoolState.from(_element == rightElement);
     } else if (rightOperand is DynamicState) {
       return BoolState.UNKNOWN_VALUE;
     }
     return BoolState.FALSE_STATE;
   }
 
   @override
   String toString() => _element == null ? "-unknown-" : _element.name;
 }