How to compile a C# file with Roslyn programmatically?

Question

I read that you can't compile C# 6.0 with CSharpCodeProvider and therefor trying to do with with Roslyn. But I can't find a good example how to load a file and then compile it to a dll.

How should I write something similar to this code with Roslyn? Or is there some other way to do it? Now when I try to compile files that contain reference to projects with C# 6.0 code it just say "The type or namespace name 'x' does not exist in the namespace 'y' (are you missing an assembly reference?)"

    public string CompileCode()
    {
        var provider = new CSharpCodeProvider();
        var outputPath = Path.Combine(Path.GetDirectoryName(_path), $"Code.dll");
        var compilerparams = new CompilerParameters(_referencedAssemblies, outputPath);
        CompilerResults results = provider.CompileAssemblyFromFile(compilerparams, _path);
        var dllPath = results.PathToAssembly;
        if (!results.Errors.HasErrors)
            return dllPath;
        PrintError(results.Errors);
        return ""; 
    }

In summary I want to:

• Load a C# file
• Compile it to a dll so I can load it later.

Nore

Another post on a similar topic: trying to compile and execute C# code programmatically – Mosenthal

Answer 1

I have created a sample for you to work with. You need to tweak it to use the run time for .Net 4.6 so that CSharp6 version is availble to you. I have added little details so that you can choose the options of compilations.

Changes required - Change the path of runtime to target .Net 4.6 Change the LanguageVersion.Csharp5 to LanguageVersion.Csharp6 in below sample.

 class Program
    {
        private static readonly IEnumerable<string> DefaultNamespaces =
            new[]
            {
                "System", 
                "System.IO", 
                "System.Net", 
                "System.Linq", 
                "System.Text", 
                "System.Text.RegularExpressions", 
                "System.Collections.Generic"
            };

        private static string runtimePath = @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5.1\{0}.dll";

        private static readonly IEnumerable<MetadataReference> DefaultReferences =
            new[]
            {
                MetadataReference.CreateFromFile(string.Format(runtimePath, "mscorlib")),
                MetadataReference.CreateFromFile(string.Format(runtimePath, "System")),
                MetadataReference.CreateFromFile(string.Format(runtimePath, "System.Core"))
            };

        private static readonly CSharpCompilationOptions DefaultCompilationOptions =
            new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
                    .WithOverflowChecks(true).WithOptimizationLevel(OptimizationLevel.Release)
                    .WithUsings(DefaultNamespaces);

        public static SyntaxTree Parse(string text, string filename = "", CSharpParseOptions options = null)
        {
            var stringText = SourceText.From(text, Encoding.UTF8);
            return SyntaxFactory.ParseSyntaxTree(stringText, options, filename);
        }

        static void Main(string[] args)
        {
            var fileToCompile = @"C:\Users\DesktopHome\Documents\Visual Studio 2013\Projects\ConsoleForEverything\SignalR_Everything\Program.cs";
            var source = File.ReadAllText(fileToCompile);
            var parsedSyntaxTree = Parse(source, "", CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp5));

            var compilation
                = CSharpCompilation.Create("Test.dll", new SyntaxTree[] { parsedSyntaxTree }, DefaultReferences, DefaultCompilationOptions);
            try
            {
                var result = compilation.Emit(@"c:\temp\Test.dll");

                Console.WriteLine(result.Success ? "Sucess!!" : "Failed");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
            Console.Read();
        }

This would need little tweaks but it should give you desired results. Change it as you may wish.

Behre

Can yo utell me what references/packages I need to get this to work? Thanks. – Miguelinamiguelita

Microsoft.CodeAnalysis.CSharp this package will install other dependencies as well. – Behre

Do not put .dll on the CSharpCompilation.Create, had a lot of work today to figure out this, thanks for the answer. – Louisville

What about compiling multiple cs files to one dll? – Gadmann

Answer 2

You have to use the NuGet package Microsoft.CodeAnalysis.CSharp.

var syntaxTree = CSharpSyntaxTree.ParseText(source);

CSharpCompilation compilation = CSharpCompilation.Create(
    "assemblyName",
    new[] { syntaxTree },
    new[] { MetadataReference.CreateFromFile(typeof(object).Assembly.Location) },
    new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));

using (var dllStream = new MemoryStream())
using (var pdbStream = new MemoryStream())
{
    var emitResult = compilation.Emit(dllStream, pdbStream);
    if (!emitResult.Success)
    {
        // emitResult.Diagnostics
    }
}

Bowers

Why do we have to get an external NuGet package for this? Is Roslyn not part of the .NET framework? – Sesquicarbonate

Roslyn in not part of the .NET Framework, so you have to get it with a NuGet package. CodeDom is part of the .NET Framework, but I think it supports only c# 5. – Bowers

@Bowers how to support some default libraries with this code? I have tried to do using System.Linq; and got compilation error The type or namespace name 'Linq' does not exist in the namespace 'System' (are you missing an assembly reference?) – Mortise

You can download the package Microsoft.NETCore.App.Ref or Microsoft.NETFramework.ReferenceAssemblies.net48 and reference the dll from the lib folder. You can find useful packages here github.com/meziantou/Meziantou.Analyzer/blob/… – Bowers