Rewrite SyntaxNode to two SyntaxNodes

问题

I'm using Roslyn's CSharpSyntaxRewriter to rewrite the following:

string myString = "Hello ";
myString += "World!";

to:

string myString = "Hello ";
myString += "World!"; Log("myString", myString);

My syntax rewriter overrides VisitAssignmentExpression as follows.

public override SyntaxNode VisitAssignmentExpression(AssignmentExpressionSyntax node)
{
    //Construct a new node without trailing trivia
    var newNode = node.WithoutTrailingTrivia();
    InvocationExpressionSyntax invocation = //Build proper invocation

    //Now what? I need to bundle up newNode and invocation and return them
    //as an expression syntax
}

I have been able to "cheat" this limitation when dealing with StatementSyntax by constructing a BlockSyntax with missing braces:

var statements = new SyntaxList<StatementSyntax>();
//Tried bundling newNode and invocation together
statements.Add(SyntaxFactory.ExpressionStatement(newNode));
statements.Add(SyntaxFactory.ExpressionStatement(invocation));
var wrapper = SyntaxFactory.Block(statements);

//Now we can remove the { and } braces
wrapper = wrapper.WithOpenBraceToken(SyntaxFactory.MissingToken(SyntaxKind.OpenBraceToken))
    .WithCloseBraceToken(SyntaxFactory.MissingToken(SyntaxKind.CloseBraceToken)

However this approach won't work with AssignmentExpressionSyntax as BlockSyntax cannot be cast to ExpressionSyntax. (The CSharpSyntaxRewriter tries to make this cast.)

How can I rewrite one SyntaxNode into two SyntaxNodes?

Have I run up against a limitation of the API, or are there any tricks similar to the above that someone could share?

回答1:

You need to visit the parent ExpressionStatementSyntax and replace that with a BlockSyntax.

You cannot insert a BlockSyntax as an expression in an expression statement.

来源：https://stackoverflow.com/questions/28802121/rewrite-syntaxnode-to-two-syntaxnodes

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roslyn