How to tell if VSCode language extension is running (logging/debugging)?

Question

I am putting together a very basic VSCode "language server" following their demo. The full source code is available here. I basically just want to do basic "tab completion" for now, but trying to get a simple hello-world example running and I'm not sure if my extension is even running, or how to debug/log in it. Some notes:

• There is a client directory, where the extension starts.
• The top-level package.json has "main": "./client/out/extension", which is compiled TypeScript output.
• There is a server directory, which has the logic for the tab completion.
• I put client.info('hello') in the client client/src/extension.ts file, but got no output.

(the screen in the back left is the extension test runner, the screen on the right is the extension source code repo).

What am I missing? How do I debug that everything is running? How do I log to the "console", and where will it show up? Can I do anything like alert('foo') like you can in the browser? (Maybe to test that the test runner shows the completion)? Any guidance would be greatly appreciated, I've never written a full extension. I will say that I did build the syntax highlighter part of the extension, and that loads fine in the test runner.

Tried this but still not seeing the output anywhere. Not sure if I'm just looking in the wrong place, or my extension isn't actually running properly.

Maybe these workers getting blocked is a problem?

Answer 1

I needed to add .vscode/launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "extensionHost",
      "request": "launch",
      "name": "Launch Client",
      "runtimeExecutable": "${execPath}",
      "args": ["--extensionDevelopmentPath=${workspaceRoot}"],
      "outFiles": ["${workspaceRoot}/client/out/**/*.js"],
      "autoAttachChildProcesses": true,
      "preLaunchTask": {
        "type": "npm",
        "script": "watch"
      }
    }
  ]
}