anchor.diff:      _EqualityOpContext<Variable, Type> context =
           _stack.removeLast() as _EqualityOpContext<Variable, Type>;
       ExpressionInfo<Variable, Type> lhsInfo = context._conditionInfo;
  +    Variable lhsVariable = context._leftOperandVariable;
       Type leftOperandType = context._leftOperandType;
       ExpressionInfo<Variable, Type> rhsInfo = _getExpressionInfo(rightOperand);
  +    Variable rhsVariable = _getExpressionVariable(rightOperand);
       TypeClassification leftOperandTypeClassification =
           typeOperations.classifyType(leftOperandType);
       TypeClassification rightOperandTypeClassification =
  
positive.code:     _expressionWithInfo = expression;
      _expressionInfo = expressionInfo;
      _current = expressionInfo.after;
    }
  }
  
  
negative.code:   /// The type of the expression on the LHS of `==` or `!=`.
    final Type _leftOperandType;
  
    /// If the LHS of `==` or `!=` is a variable reference, the variable.
    /// Otherwise `null`.
    final Variable _leftOperandVariable;
  
    _EqualityOpContext(ExpressionInfo<Variable, Type> conditionInfo,
        this._leftOperandType, this._leftOperandVariable)
        : super(conditionInfo);
  
    @override
  