anchor.diff:    bool _isValidMixin = false;
   
     /**
  +   * A collection holding the elements defined in a class that need to have
  +   * their function type fixed to take into account type parameters of the
  +   * enclosing class, or `null` if we are not currently processing nodes within
  +   * a class.
  +   */
  +  List<ExecutableElementImpl> _functionTypesToFix = null;
  +
  +  /**
      * A table mapping field names to field elements for the fields defined in the current class, or
      * `null` if we are not in the scope of a class.
      */
  
positive.code:     InterfaceTypeImpl interfaceType = new InterfaceTypeImpl(element);
      interfaceType.typeArguments = typeArguments;
      element.type = interfaceType;
      List<ConstructorElement> constructors = holder.constructors;
      if (constructors.length == 0) {
        //
        // Create the default constructor.
        //
        constructors = _createDefaultConstructors(interfaceType);
      }
      _setDocRange(element, node);
      element.abstract = node.isAbstract;
      element.accessors = holder.accessors;
      element.constructors = constructors;
      element.fields = holder.fields;
      element.methods = holder.methods;
      element.typeParameters = typeParameters;
      element.validMixin = _isValidMixin;
      _currentHolder.addType(element);
      className.staticElement = element;
      _fieldMap = null;
  
negative.code:         element.setVisibleRange(functionEnd, blockEnd - functionEnd - 1);
        }
      }
      if (_functionTypesToFix != null) {
        _functionTypesToFix.add(element);
      } else {
        // TODO(jmesserly): for local functions inside of top-level generic
        // functions, this is probably not right. The function type should be set
        // after the enclosingElement is set, otherwise we won't be able to
        // substitute those type parameters later.
        element.type = new FunctionTypeImpl(element);
      }
      element.hasImplicitReturnType = true;
      _currentHolder.addFunction(element);
      node.element = element;
  