Automatically resolving dependencies when compiling using Roslyn

Question

I'm currently writing an application that currently loads a project via Roslyn's workspace API, turns a specified C# file into a syntax tree then creates an in memory assembly form it, then eventually extracts the IL.

This is all working fine, however as soon as I reference any external libraries within the said C# file, the compilation fails as Roslyn doesn't know where to resolve those references.

Here's a simplified version of what I'm currently doing:

MetadataReference[] metaDatareferences = {
    MetadataReference.CreateFromFile(typeof(object).GetTypeInfo().Assembly.Location),
    MetadataReference.CreateFromFile(typeof(Uri).GetTypeInfo().Assembly.Location),
    MetadataReference.CreateFromFile(typeof(DynamicAttribute).GetTypeInfo().Assembly.Location),
    MetadataReference.CreateFromFile(typeof(AssemblyMetadata).GetTypeInfo().Assembly.Location),
};

var sourceLanguage = new CSharpLanguage();

var syntaxTree = sourceLanguage.ParseText(sourceCode, SourceCodeKind.Regular);
var options = new CSharpCompilationOptions(
    OutputKind.DynamicallyLinkedLibrary,
    optimizationLevel: OptimizationLevel.Debug,
    allowUnsafe: true
);

CSharpCompilation compilation = CSharpCompilation.Create("ExampleAssembly", options: options);

var stream = new MemoryStream();
var result = compilation.
    AddReferences(metaDatareferences)
    .AddSyntaxTrees(syntaxTree)
    .Emit(stream);

// Success is false
if (!emitResult.Success)
{
    foreach (var diagnostic in emitResult.Diagnostics)
    {
        Debug.WriteLine(diagnostic.ToString());
    }
}

The output of the Debug.WriteLine is:

(1,7): error CS0246: The type or namespace name 'MediatR' could not be found (are you missing a using directive or an assembly reference?)
(9,32): error CS0246: The type or namespace name 'Mediator' could not be found (are you missing a using directive or an assembly reference?)

And the file my Roslyn project is reading is simply this:

using MediatR;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var mediator = new Mediator(null, null);
        }
    }
}

My question is, does Roslyn provide an API for automatically load any dependencies a file may have? I was hopeful that the Roslyn workspace would allow this to be done, but I've not been able to find anything.

Are you sure it's due to not being able to load references, and not e.g. some syntax error? Show us the exact compiler error. — Kris Vandermotten
I've updated my question to include the error output and the file I'm reading. — Joseph Woodward
so, you're hoping the using MediatR; directive would resolve your lib? That's why you have #r <path> in CSharpScript. Even MetadataReferences need to be resolved, see MetadataReferenceResolver. They only way of achieving this I can think of would be to #1 compile, #2 check known errors, try to add references, goto #1. But even that wouldn't work for extension methods etc, that share a namespace... — m0sa♦
@m0sa No, this isn't a C# Script file. My intention is to compile a random C# pulled from a project's workspace. — Joseph Woodward
When you say you are loading a file "from a project", do you have a .csproj or project.json or something around to look at? — Jason Malinowski

Stuart Stuart · Accepted Answer · 2017-01-11T08:28:17

If the MediatR console project is a project.json project, then you can use ProjectJsonWorkspace from "Microsoft.DotNet.ProjectModel.Workspaces": "1.0.0-preview2-1-003177". You can point it at your project.json and get a Compilation object, this will have done all the hard work for you of getting the project references, file references, etc... Then you can just emit your IL from here.

Here is an example:

var compilation = new ProjectJsonWorkspace(@"PathToYour\project.json").CurrentSolution.Projects.First().GetCompilationAsync().Result;

var stream = new MemoryStream();
var emitResult = compilation.Emit(stream);

Or if you need total control, you could continue to use CSharpCompilation.Create, copying in what you need from the compilation object here, and passing in a SyntaxTree.

Hope that helps.

Automatically resolving dependencies when compiling using Roslyn

1 Answers