Implement correct scoping rules for variables.

sdk/lib/_internal/compiler/implementation/resolution/scope.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.
 
 part of resolution;
 
 abstract class Scope {
   /**
    * Adds [element] to this scope. This operation is only allowed on mutable
    * scopes such as [MethodScope] and [BlockScope].
@@ skipping 23 matching lines @@
   }
 
   Element localLookup(SourceString name);
 
   static Scope buildEnclosingScope(Element element) {
     return element.enclosingElement != null
         ? element.enclosingElement.buildScope() : element.buildScope();
   }
 }
 
-class VariableDefinitionScope extends NestedScope {
-  final SourceString variableName;
-  bool variableReferencedInInitializer = false;
-
-  VariableDefinitionScope(Scope parent, this.variableName) : super(parent);
-
-  Element localLookup(SourceString name) {
-    if (name == variableName) {
-      variableReferencedInInitializer = true;
-    }
-    return null;
-  }
-
-  Element add(Element newElement) {
-    throw "Cannot add element to VariableDefinitionScope";
-  }
-}
-
 /**
  * [TypeDeclarationScope] defines the outer scope of a type declaration in
  * which the declared type variables and the entities in the enclosing scope are
  * available but where declared and inherited members are not available. This
  * scope is only used for class declarations during resolution of the
  * class hierarchy. In all other cases [ClassScope] is used.
  */
 class TypeDeclarationScope extends NestedScope {
   final TypeDeclarationElement element;
 
   TypeDeclarationScope(parent, this.element)
       : super(parent) {
     assert(parent != null);
   }
 
   Element add(Element newElement) {
-    throw "Cannot add element to TypeDeclarationScope";
+    throw "Cannot add element to TypeDeclarationScope($element)";
   }
 
   Element lookupTypeVariable(SourceString name) {
     Link<DartType> typeVariableLink = element.typeVariables;
     while (!typeVariableLink.isEmpty) {
       TypeVariableType typeVariable = typeVariableLink.head;
       if (typeVariable.name == name) {
         return typeVariable.element;
       }
       typeVariableLink = typeVariableLink.tail;
     }
     return null;
   }
 
   Element localLookup(SourceString name) => lookupTypeVariable(name);
 
   String toString() =>
       'TypeDeclarationScope($element)';
 }
 
-abstract class MutableScope extends NestedScope {
+class BlockScope extends NestedScope {
   final Map<SourceString, Element> elements;
 
-  MutableScope(Scope parent)
-      : super(parent),
-        this.elements = new Map<SourceString, Element>() {
+  BlockScope(Scope parent)
+      : elements = <SourceString, Element>{}, super(parent) {
     assert(parent != null);
   }
 
-  Element add(Element newElement) {
-    if (elements.containsKey(newElement.name)) {
-      return elements[newElement.name];
-    }
-    elements[newElement.name] = newElement;
-    return newElement;
+  Element add(Element element) {
+    return elements.putIfAbsent(element.name, () => element);
   }
 
   Element localLookup(SourceString name) => elements[name];
+
+  String toString() => 'BlockScope(${elements.keys.toList()})';
 }
 
-class MethodScope extends MutableScope {
+class MethodScope extends BlockScope {
   final Element element;
 
-  MethodScope(Scope parent, this.element)
-      : super(parent);
+  MethodScope(Scope parent, this.element) : super(parent) {
+    assert(elements != null);
+  }
 
   String toString() => 'MethodScope($element${elements.keys.toList()})';
 }
 
-class BlockScope extends MutableScope {
-  BlockScope(Scope parent) : super(parent);
-
-  String toString() => 'BlockScope(${elements.keys.toList()})';
-}
-
 /**
  * [ClassScope] defines the inner scope of a class/interface declaration in
  * which declared members, declared type variables, entities in the enclosing
  * scope and inherited members are available, in the given order.
  */
 class ClassScope extends TypeDeclarationScope {
   ClassElement get element => super.element;
 
   ClassScope(Scope parentScope, ClassElement element)
       : super(parentScope, element)  {
@@ skipping 28 matching lines @@
 
   Element localLookup(SourceString name) => library.find(name);
   Element lookup(SourceString name) => localLookup(name);
 
   Element add(Element newElement) {
     throw "Cannot add an element to a library scope";
   }
 
   String toString() => 'LibraryScope($library)';
 }