Roslyn scripting: Line number information for run time exceptions

Question

I am messing around with the Roslyn scripting stuff (using the Microsoft.CodeAnalysis.CSharp.Scripting nuget package), and I wonder if there is a way to add line number information to the stack traces for exceptions that happen inside a script.

When I run the following C# code:

// using Microsoft.CodeAnalysis.CSharp.Scripting;

var code = @"
var a = 0;
var b = 1 / a;
";
try
{
    await CSharpScript.RunAsync(code);
}
catch (DivideByZeroException dbze)
{
    Console.WriteLine(dbze.StackTrace);
}

The stack trace written to the console is:

   at Submission#0.<<Initialize>>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.CodeAnalysis.Scripting.ScriptExecutionState.<RunSubmissionsAsync>d__9`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.CodeAnalysis.Scripting.Script`1.<RunSubmissionsAsync>d__21.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at UnitTests.ExploreRoslyn.<ScriptWithRuntimeError>d__4.MoveNext() in D:\dev\misc\netmockery\UnitTests\ExploreRoslyn.cs:line 47

Note that if I try to catch the exception inside the script, the result is similar:

var code = @"
try  {
    var a = 0;
    var b = 1 / a;
}
catch (System.DivideByZeroException dbze)
{
    Console.WriteLine(dbze.StackTrace);
}
";
await CSharpScript.RunAsync(code);

This outputs:

at Submission#0.<<Initialize>>d__0.MoveNext()

To the console.

Is there a way to make the Roslyn scripting engine add debug information when compiling/executing the script, so I can get line number information in the stack trace?

Answer 1

I got something working by emitting an (in-memory) assembly with debug information.

Example code:

var code = @"
var a = 0;
var b = 1 / a;
";

var script = CSharpScript.Create(code);
var compilation = script.GetCompilation();
var ilstream = new MemoryStream();
var pdbstream = new MemoryStream();
compilation.Emit(ilstream, pdbstream);

var assembly = Assembly.Load(ilstream.GetBuffer(), pdbstream.GetBuffer());
var type = assembly.GetType("Submission#0");
var factory = type.GetMethod("<Factory>");
var submissionArray = new object[2];
Task<object> task = (Task<object>)factory.Invoke(null, new object[] { submissionArray });

try
{
    await task;
}
catch (DivideByZeroException dbze)
{
    Console.WriteLine(dbze.StackTrace);
}

The output is (notice the :line 3 in the stack trace):

   at Submission#0.<<Initialize>>d__0.MoveNext() in :line 3
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at UnitTests.ExploreRoslyn.<ExploreEmittingAssembly>d__13.MoveNext() in D:\dev\misc\netmockery\UnitTests\ExploreRoslyn.cs:line 151

Now obviously this is a bit of a hack, and I'm not really happy with the hardcoded script engine implementation details (Submission#0, <Factory>), plus I don't really know what I'm doing. There should be (and maybe there is?) a better way.

Update

Created issue https://github.com/dotnet/roslyn/issues/13482 in the Roslyn issue tracker.