Question: VSTest/MTP debugger integration

[GustavEikaas]

Hello,

Description

I got such good help last time in #5487 and #3725. I was wondering if there are any examples/docs on how to make vstest and MTP request a debugger?

For context I am building a neovim plugin for dotnet development. This is accompanied by a JSON-RPC C# "IDE" server which handles the more complex features. I am able to programatically discover and run tests both in VSTest and MTP using Translation layer and RPC. But for both I am confused on how to make them request a debugger

VSTest

internal sealed class TestRunHandler() : ITestRunEventsHandler
{
  public List<TestResult> Results = [];

  public void HandleLogMessage(TestMessageLevel level, string? message) { }

  public void HandleRawMessage(string rawMessage) { }

  public void HandleTestRunComplete(TestRunCompleteEventArgs testRunCompleteArgs, TestRunChangedEventArgs? lastChunkArgs, ICollection<AttachmentSet>? runContextAttachments, ICollection<string>? executorUris) { }
  public void HandleTestRunStatsChange(TestRunChangedEventArgs? testRunChangedArgs)
  {
    if (testRunChangedArgs?.NewTestResults is not null)
    {
      Results.AddRange(testRunChangedArgs.NewTestResults);
    }
  }

// How to make vstest call this so i can hook in my debugger?
  public int LaunchProcessWithDebuggerAttached(TestProcessStartInfo testProcessStartInfo) => throw new NotImplementedException();
}

MTP

I start the server with these flags
--server --client-host localhost --client-port {port} --diagnostic --diagnostic-verbosity trace

internal class MtpRpc
{
  //how to make server call this?
  [JsonRpcMethod("client/attachDebugger", UseSingleObjectParameterDeserialization = true)]
  public static Task AttachDebuggerAsync(AttachDebuggerInfo attachDebuggerInfo) => throw new NotImplementedException();

  [JsonRpcMethod("testing/testUpdates/tests")]
  public Task TestsUpdateAsync(Guid runId, TestNodeUpdate[]? changes)
  {
//....
  }
}

Hopefully my question is both in right repo and makes sense

[nohwnd]

The naming in vstest is terrible but you do it either via this command, which will tell the runner to run with custom testhost launcher.
historically vstest would ask visual studio to start testhost for it, and attach debugger. In modern times we start testhost ourselves and then ask VS to attach debugger to it. It both got smushed into the same interface, ITestHostLauncher2.

r.RunTestsWithCustomTestHost(sources, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput), new DebuggerTestHostLauncher());

Executable version of that is shown here:
https://github.com/microsoft/vstest/blob/main/playground/TestPlatform.Playground/Program.cs#L154

For modern flow with modern .net testhosts you can only implement the AttachMethods, and the launch methods can throw.

the TestRunRequestPayload needs to set: DebuggingEnabled = true.

More details about the flow of messages: https://github.com/microsoft/vstest/blob/main/docs/Overview.md#run

[GustavEikaas]

Thanks for the detailed answer.

I made an instance of ITestHostLauncher2 and ran it with RunTestsWithCustomTestHost that worked for me and I can now make the client attach a debugger. I'm not sure if that is the "old" way of doing it? You wrote some details around modern flow but i'm not sure how that correlates with my code. Is it a totally different setup or? Sorry if it's a totally noob question

For my MTP integration I dont use vstest or translation layer at all. Don't think I can? Do you know how to achieve the same functionality? Where I tell MTP that I want to attach a debugger

[nohwnd]

Attach is the new flow, Launch is the old flow.

You should be able to implement just the Attach flow, and throw from the Launch flow. As long as you use vstest.console 17+ (we are on 18.0 currently).

[GustavEikaas]

Ah okay perfect that is what I ended up doing!

Okay I think im 100% on VSTest now I just need to figure out how to do the same in MTP

[nohwnd]

@drognanar please answer for MTP.

[drognanar]

the RPC is there, but I don't think we provided any services that can be queried in order to make the call. and it looks like the code to make the JSON-RPC request was removed from the testfx codebase

VS uses the initialize handshake, where if the "initialize" response contains { "processId": ID } during the debug session, it will automatically attach debugger to that process. but it also supports the RPC methods.

to implement a public API for extension authors on the MTP side, my thought here would be to implement a new interface:

interface IDebugLauncher {
  Task AttachDebugger(int pid, CancellationToken cancellationToken);
}

and then add it to the service provider on server mode construction. so a user could to serviceProvider.GetService<IDebugLauncher>() when creating an MTP extension

@Youssef1313 thoughts?

[nohwnd]

Still not super clear to me what client should implement. From the docs on protocol here: https://github.com/microsoft/testfx/blob/main/docs/mstest-runner-protocol/001-protocol-intro.md#determine-capabilities-during-test-runner-initialization

It says that we send request Initialize to the server (e.g. MyTests.exe), and it responds with the described response that either contains ProcessId, or not. Depending on whether the server was started by someone else.

So what exactly are the steps taken in the IDE?

Start the provided EXE with debugger attached? Start it without debugger and wait for initialize response and then attach what PID?

What if the provided EXE ends up running as testhost controller with the real test exe running as child?

[drognanar]

At the moment the IDE will launch the EXE with debugger attached (as there are some features that IDE only enables if it launches a debugged process).

Then if the test exe runs as a child and responds with { "processId": ID }. IDE detects that it's not the same process as the one it started and attaches to it.