anchor.diff:    /// Otherwise `null`.
     ReferenceWithType<Variable, Type>? _expressionReference;
   
  -  int _functionNestingLevel = 0;
  -
     final AssignedVariables<Node, Variable> _assignedVariables;
   
     /// Indicates whether initializers of implicitly typed variables should be
  
positive.code:   void functionExpression_begin(Node node) {
      AssignedVariablesNodeInfo<Variable> info =
          _assignedVariables._getInfoForNode(node);
      ++_functionNestingLevel;
      _current = _current.conservativeJoin(const [], info._written);
      _stack.add(new _FunctionExpressionContext(_current));
      _current = _current.conservativeJoin(_assignedVariables._anywhere._written,
  
negative.code: 
    @override
    void functionExpression_end() {
      _SimpleContext<Variable, Type> context =
          _stack.removeLast() as _FunctionExpressionContext<Variable, Type>;
      _current = context._previous;
  