anchor.diff:      _expressionWithInfo = expression;
       _expressionInfo = expressionInfo;
       _current = expressionInfo.after;
  +  }
  +
  +  /// Associates [expression], which should be the most recently visited
  +  /// expression, with the given [Variable] object.
  +  void _storeExpressionVariable(
  +      Expression expression, Variable expressionVariable) {
  +    _expressionWithVariable = expression;
  +    _expressionVariable = expressionVariable;
     }
   }
   
  
positive.code:   /// The type of the expression on the LHS of `==` or `!=`.
    final Type _leftOperandType;
  
    _EqualityOpContext(
        ExpressionInfo<Variable, Type> conditionInfo, this._leftOperandType)
        : super(conditionInfo);
  
    @override
  
negative.code:   /// corresponding to it.  Otherwise `null`.
    ExpressionInfo<Variable, Type> _expressionInfo;
  
    /// The most recently visited expression which was a variable reference, or
    /// `null` if no expression has been visited that was a variable reference.
    Expression _expressionWithVariable;
  
    /// If [_expressionVariable] is not `null`, the variable corresponding to it.
    /// Otherwise `null`.
    Variable _expressionVariable;
  
    int _functionNestingLevel = 0;
  
    final AssignedVariables<Node, Variable> _assignedVariables;
  