CODEWITHSUNDEEP
c#vb.netparsingroslyn
Paul Cohen
Paul Cohen

Reputation: 271

How do you parse Roslyn SyntaxTrivia

I want to look into Roslyn SyntaxTrivia and view the pieces in VB code but I don't see anyway to pick apart the pieces of the various types. There are many types, just for C# I found the types below (not complete). Usually in Roslyn you can cast an object to a more specific type and then look at the language specific parts. I don't see how to do that with Trivia.

DocumentationCommentExteriorTrivia
EndOfLineTrivia
EndRegionDirectiveTrivia
MultiLineCommentTrivia
MultiLineDocumentationCommentTrivia
RegionDirectiveTrivia
SingleLineCommentTrivia
WhitespaceTrivia

Upvotes: 0

Views: 1231

Answers (1)

SJP
SJP

Reputation: 1010

Most Trivia are just that - trivia without further information. However, some trivia contain SyntaxNodes which you can parse und process as usual with a small difference - you need to tell your methods that you want to find them. These are not SyntaxTrivias, but StructuredTriviaSyntax elements and you can find them as follows:

// C#
var structuredTriviaSyntax = root.DescendantNodes(
                                    descendIntoTrivia: true)
                                        .OfType<StructuredTriviaSyntax>();

// VB
Dim structuredTriviaSyntax = root.DescendantNodes(
                                    descendIntoTrivia:=True)
                                        .OfType(Of StructuredTriviaSyntax)

You can get the StructuredTrivia from a SyntaxTrivia Object by calling the GetStructure method of a SyntaxTrivia object like this:

// C#
var leadingTrivia = anySyntaxNode.GetLeadingTrivia();
foreach(var trivia in leadingTrivia){
    var structure = trivia.GetStructure();
}

// VB
Dim leadingTrivia = anySyntaxNode.GetLeadingTrivia
For Each trivia In leadingTrivia
    Dim structureNode = trivia.GetStructure
Next

This does not work for all types of trivia, as most trivia kinds do not have a SyntaxNode representation, but for instance DocumentationCommentTriviaSyntax as well as RegionDirectiveTriviaSyntax and EndRegionDirectiveTriviaSyntax are provided with more specific types which can be analyzed that way.

If you work with a SyntaxWalker or a SyntaxRewriter you need to pass "true" as a parameter in the constructor to search through trivia.

A DocumentationCommentTriviaSyntax for instance can then be analyzed by taking a look at the DescendandNodes which are various kinds of Xml[...]Syntax elements.

Upvotes: 3

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