Get the SyntaxNode given the linenumber in a SyntaxTree

Question

I want to get the SyntaxNode of a line given the location(lineNumber). The code below should be self-explanatory, but let me know of any questions.

static void Main()
        {
            string codeSnippet = @"using System;
                                        class Program
                                        {
                                            static void Main(string[] args)
                                            {
                                                Console.WriteLine(""Hello, World!"");
                                            }
                                        }";

            SyntaxTree tree = SyntaxTree.ParseCompilationUnit(codeSnippet);
            string[] lines = codeSnippet.Split('\n');
            SyntaxNode node = GetNode(tree, 6); //How??
        }

        static SyntaxNode GetNode(SyntaxTree tree,int lineNumber)
        {
            throw new NotImplementedException();
            // *** What I did ***
            //Calculted length from using System... to Main(string[] args) and named it (totalSpan)
            //Calculated length of the line(lineNumber) Console.Writeline("Helllo...."); and named it (lineSpan)
            //Created a textspan : TextSpan span = new TextSpan(totalSpan, lineSpan);
            //Was able to get back the text of the line : tree.GetLocation(span);
            //But how to get the SyntaxNode corresponding to that line??
        }

Answer 1

First, to get TextSpan based on a line number, you can use the indexer of Lines of the SourceText returned by GetText() (but careful, it counts lines from 0).

Then, to get all nodes that intersect that span, you can use an overload of DescendantNodes().

Finally, you filter that list to get the first node that is contained fully in that line.

In code:

static SyntaxNode GetNode(SyntaxTree tree, int lineNumber)
{
    var lineSpan = tree.GetText().Lines[lineNumber - 1].Span;
    return tree.GetRoot().DescendantNodes(lineSpan)
        .First(n => lineSpan.Contains(n.Span));
}

If there is no node on that line, this will throw an exception. If there is more than one, it will return the first one.