Roslyn Scripting Syntax Tree

The Syntax API exposes the syntax trees that are used by the compilers to understand C# and Visual Basic programs.

• The syntax trees are produced by the same parser that runs when a project is built.
• Every bit of information in a code file is represented in the tree, including things like comments or whitespace.

The following example shows the syntax tree of a simple hello world program.

static void SyntaxTreeExample1()
{
    SyntaxTree tree = CSharpSyntaxTree.ParseText(
        @"using System;
        using System.Collections;
        using System.Linq;
        using System.Text;
         
        namespace HelloWorld
        {
            class Program
            {
                static void Main(string[] args)
                {
                    Console.WriteLine(""Hello, World!"");
                }
            }
        }");

    var root = (CompilationUnitSyntax)tree.GetRoot();

    var firstMember = root.Members[0];
    var helloWorldDeclaration = (NamespaceDeclarationSyntax)firstMember;
    var programDeclaration = (ClassDeclarationSyntax)helloWorldDeclaration.Members[0];
    var mainDeclaration = (MethodDeclarationSyntax)programDeclaration.Members[0];
    var argsParameter = mainDeclaration.ParameterList.Parameters[0];
}

You can also explore the syntax tree using the query methods defined on SyntaxNode. You can use these methods with LINQ to quickly find things in a tree.

static void SyntaxTreeExample2()
{
    SyntaxTree tree = CSharpSyntaxTree.ParseText(
        @"using System;
        using System.Collections;
        using System.Linq;
        using System.Text;
         
        namespace HelloWorld
        {
            class Program
            {
                static void Main(string[] args)
                {
                    Console.WriteLine(""Hello, World!"");
                }
            }
        }");

    var root = (CompilationUnitSyntax)tree.GetRoot();

    var parameters = root.DescendantNodes().OfType<MethodDeclarationSyntax>()
        .Where(md => md.Identifier.ValueText == "Main")
        .Select(md => md.ParameterList.Parameters.First());

    Console.WriteLine(parameters.FirstOrDefault());
}