Roslyn Scripting API on .NET Core: why does compiler complain "error CS1501: no overload for WriteLine takes 2 arguments"?

Question

I'm working on a project targeting netcoreapp1.0 on OSX, and I'm setting up a script using Roslyn like this:

var scriptText = File.ReadAllText(args[0]);

var scriptOptions = ScriptOptions.Default
    .WithReferences(
        typeof(System.Object).GetTypeInfo().Assembly
    );

var script = CSharpScript.Create(scriptText, scriptOptions, typeof(Globals));

var scriptArgs = new string[args.Length-1];
Array.Copy(args, 1, scriptArgs, 0, args.Length-1);

script.RunAsync(new Globals
{ 
    Args = scriptArgs
})
.GetAwaiter().GetResult();

Where Globals is:

public class Globals
{
    public string[] Args { get; set; }
}

When I try to run a script that looks like this:

using System;

Console.WriteLine("Args[0]: {0}", Args[0]);

The program terminates with this exception:

$ dotnet run test.csx
Project BitThicket.DotNet.ScriptTool (.NETCoreApp,Version=v1.0) was previously compiled. Skipping compilation.
Script error: Microsoft.CodeAnalysis.Scripting.CompilationErrorException: (7,9): error CS1501: No overload for method 'WriteLine' takes 2 arguments
   at Microsoft.CodeAnalysis.Scripting.ScriptBuilder.ThrowIfAnyCompilationErrors(DiagnosticBag diagnostics, DiagnosticFormatter formatter)
   at Microsoft.CodeAnalysis.Scripting.ScriptBuilder.CreateExecutor[T](ScriptCompiler compiler, Compilation compilation, CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.Scripting.Script`1.GetExecutor(CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.Scripting.Script`1.RunAsync(Object globals, Func`2 catchException, CancellationToken cancellationToken)
   at BitThicket.DotNet.ScriptTool.Program.Main(String[] args) in /Users/ben/proj/bt/dotnet-scriptcs/src/BitThicket.DotNet.ScriptTool/Program.cs:line 63

Obviously Console does, in fact, have an overload that takes 2 methods. I looked at the CoreFx sources briefly to see if there were any odd type-forwarding or extension method tricks being used that might need additional care in the script setup, but I didn't see anything unusual there (maybe I missed something).

Why would the Roslyn ScriptBuilder then complain about this?

Answer 1

In .NET Core, the Console class is in the System.Console assembly, so you'll need to add it to the script's references:

var scriptOptions = ScriptOptions.Default
    .WithReferences(
        typeof(System.Object).GetTypeInfo().Assembly,
        typeof(System.Console).GetTypeInfo().Assembly
    );

If you check the assembly location of Object, you'll see it's System.Private.CoreLib.ni.dll. Using ILSpy, we can see this assembly only contains a basic Console implementation, with the methods Write(string s), WriteLine(string s) and WriteLine(). Whereas the System.Console assembly contains the full implementation.