Using System.Dynamic in Roslyn

Question

I modified the example that comes with the new version of Roslyn that was released yesterday to use dynamic and ExpandoObject but I am getting a compiler error which I am not sure how to fix. The error is:

(7,21): error CS0656: Missing compiler required member 'Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo.Create'

Can you not use dynamics in the new compiler yet? How can I fix this? Here is the example that I updated:

[TestMethod]
public void EndToEndCompileAndRun()
{
    var text = @"using System.Dynamic;
    public class Calculator
    {
        public static object Evaluate()
        {
            dynamic x = new ExpandoObject();
            x.Result = 42;
            return x.Result;
        } 
    }";

    var tree = SyntaxFactory.ParseSyntaxTree(text);
    var compilation = CSharpCompilation.Create(
        "calc.dll",
        options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary),
        syntaxTrees: new[] {tree},
        references: new[] {new MetadataFileReference(typeof (object).Assembly.Location), new MetadataFileReference(typeof (ExpandoObject).Assembly.Location)});

    Assembly compiledAssembly;
    using (var stream = new MemoryStream())
    {
        var compileResult = compilation.Emit(stream);
        compiledAssembly = Assembly.Load(stream.GetBuffer());
    }

    Type calculator = compiledAssembly.GetType("Calculator");
    MethodInfo evaluate = calculator.GetMethod("Evaluate");
    string answer = evaluate.Invoke(null, null).ToString();

    Assert.AreEqual("42", answer);
}

Answer 1

I think that you should reference the Microsoft.CSharp.dll assembly

Answer 2

To make the code work in .Net Core 2.1 I had to add this references in the compilation:

var compilation = CSharpCompilation.Create(
    "calc.dll",
    options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary),
    syntaxTrees: new[] {tree},
    references: new[] {
        MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
        MetadataReference.CreateFromFile(typeof(ExpandoObject).Assembly.Location),
        MetadataReference.CreateFromFile(Assembly.Load(new AssemblyName("Microsoft.CSharp")).Location),
        MetadataReference.CreateFromFile(Assembly.Load(new AssemblyName("netstandard")).Location),
        MetadataReference.CreateFromFile(Assembly.Load(new AssemblyName("mscorlib")).Location),
        MetadataReference.CreateFromFile(Assembly.Load(new AssemblyName("System.Runtime")).Location),            
    }
);

Answer 3

ASP.NET MVC specific:

You can get this error in an MVC 6 controller if you forget to put [FromBody] in a POST method.

    [HttpPost("[action]")]
    public void RunReport([FromBody]dynamic report)
    {
        ...
    }

The .NETCore default project already includes Microsoft.CSharp reference but you get pretty much the same message.

With [FromBody] added you can now post JSON and then just dynamically access the properties :-)

Answer 4

You may also want to check the properties of all your project references. Make sure any reference is using .NET newer than 2.0. I have a project that was referencing another project in the same solution and had to rebuild the dependency using a newer .NET framework target.

See this post.

Also, don't forget to add the Microsoft.CSharp reference to you main project like @Alberto said.

Answer 5

If your project is targeting .Net Core or .Net Standard, then instead of adding reference you can install the Microsoft.CSharp NuGet package to solve this error.