Adding reference and modifying document

gistfile1.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.MSBuild;

namespace ConsoleApplication11
{
    class Program
    {
        static void Main(string[] args)
        {
            var workspace = MSBuildWorkspace.Create();
            RunAsync(workspace, args).GetAwaiter().GetResult(); ;
        }

        private static async Task RunAsync(MSBuildWorkspace workspace, string[] args)
        {
            var solution = await workspace.OpenSolutionAsync(args[0]);
            var project = solution.Projects.Single();
            var projectWithReference = project.AddMetadataReference(MetadataReference.CreateFromFile(@"path\to\reference.dll"));
            var docuemnt = projectWithReference.Documents.Single();
            var reWritenDocument = Rewrite(docuemnt);
            var compilation = await reWritenDocument.Project.GetCompilationAsync();
            var diagnostics = compilation.GetDiagnostics();
            foreach (var diagnostic in diagnostics)
            {
                Console.WriteLine(diagnostic);
            }
        }

        private static Document Rewrite(Document document)
        {
            // change document to call the static method
            throw new NotImplementedException();
        }
    }
}