SyntaxRewriter和多个语句

Question

我在Roslyn中使用SyntaxRewriter遇到了棘手的情况.我想重写某些类型的语句,包括局部变量声明.该解决方案要求我将有问题的语句转换为多个语句,如下面的简单示例所示:

void method()
{
    int i;
}

变

void method()
{
    int i;
    Console.WriteLine("I declared a variable.");
}

我已经看到了其他使用块来完成类似事情的例子,当然在变量声明的情况下,声明的范围也会受到影响.我提出了以下解决方案,但我正在喋喋不休.它似乎过于复杂,需要中断访问者模式:

class Rewriter: SyntaxRewriter
{
    public override SyntaxList<TNode> VisitList<TNode>(SyntaxList<TNode> list)
    {
        if (typeof(TNode) == typeof(StatementSyntax))
            return Syntax.List<TNode>(list.SelectMany(st => RewriteStatementInList(st as StatementSyntax).Cast<TNode>()));
        else
            return base.VisitList<TNode>(list);
    }

    private IEnumerable<SyntaxNode> RewriteStatementInList(StatementSyntax node)
    {
        if (node is LocalDeclarationStatementSyntax)
            return PerformRewrite((LocalDeclarationStatementSyntax)node);
        //else if other cases (non-visitor) 

        return Visit(node).AsSingleEnumerableOf();
    }

    private IEnumerable<SyntaxNode> PerformRewrite(LocalDeclarationStatementSyntax orig)
    {
        yield return orig;
        yield return Syntax.ParseStatement("Console.WriteLine(\"I declared a variable.\");");
    }
}

我错过了什么？编辑语句并删除它们(通过空语句)似乎比重写多次更直接.

我接受了答案:

class Rewriter : SyntaxRewriter
{
    readonly ListVisitor _visitor = new ListVisitor();

    public override SyntaxList<TNode> VisitList<TNode>(SyntaxList<TNode> list)
    {
        var result = Syntax.List(list.SelectMany(_visitor.Visit).Cast<TNode>());
        return base.VisitList(result);
    }

    private class ListVisitor : SyntaxVisitor<IEnumerable<SyntaxNode>>
    {
        protected override IEnumerable<SyntaxNode> DefaultVisit(SyntaxNode node)
        {
            yield return node;
        }

        protected override IEnumerable<SyntaxNode> VisitLocalDeclarationStatement(
             LocalDeclarationStatementSyntax node)
        {
            yield return node;
            yield return Syntax.ParseStatement("Console.WriteLine(\"I declared a variable.\");");
        }
    }
}

Answer 1

我认为有一种简单的方法可以让您Rewriter更像访问者：使用另一个访问者来处理列表中的节点：

class Rewriter: SyntaxRewriter
{
    readonly Visitor m_visitor = new Visitor();

    public override SyntaxList<TNode> VisitList<TNode>(SyntaxList<TNode> list)
    {
        var result = Syntax.List(list.SelectMany(m_visitor.Visit).Cast<TNode>());
        return base.VisitList(result);
    }
}

class Visitor : SyntaxVisitor<IEnumerable<SyntaxNode>>
{
    protected override IEnumerable<SyntaxNode> DefaultVisit(SyntaxNode node)
    {
        return new[] { node };
    }

    protected override IEnumerable<SyntaxNode> VisitLocalDeclarationStatement(
         LocalDeclarationStatementSyntax node)
    {
        return new SyntaxNode[]
               {
                   node,
                   Syntax.ParseStatement(
                       "Console.WriteLine(\"I declared a variable.\");")
               };
    }
}

请注意，这不安全，InvalidCastException如果您返回包含不是TNode来自Visitor.