PreLaunchTask correctly waits for background task to wait for client connection, then fails with vague popuop

[jasondamour]

Environment data

• debugpy version: 1.8.6
• OS and version: MacOS (ARM) 14.6.1
• Python version: 3.10.6
• Using VS Code or Visual Studio: VS Code

Actual behavior

I'm using Pants to run python tests. The program behaves as expected (starts the test with pdb and waits for client connection):

➜  pants test --debug-adapter example_test.py
12:16:25.45 [INFO] Launching debug adapter at '127.0.0.1:5678', which will wait for a client connection...

I would like to use a launch configuration with a preLaunchTask to make debugging easy. However, VS Code does not behave as expected with the background task. I have tried seemingly every possible combination of isBackground, problemMatcher.background, and other fields. Below is what I believe should work according to documentation. When the "Pants: Debug Test" launch configuration is triggered, it calls the correct shell command and correctly waits for the "Launching debug adapter" endPattern to be printed, but then fails with a vague popup

launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Pants: Debug Test",
      "preLaunchTask": "Pants Debug Test (Current File)",
      "type": "debugpy",
      "request": "attach",
      "pathMappings": [
        {
          "localRoot": "${workspaceFolder}",
          "remoteRoot": "."
        }
      ],
      "connect": {
        "host": "localhost",
        "port": 5678
      }
    }
  ]
}

tasks.json:

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "Pants Debug Test (Current File)",
      "type": "shell",
      "command": "pants test --debug-adapter ${file} ",
      "group": "test",
      "presentation": {
        "echo": true,
        "reveal": "always",
        "focus": false,
        "panel": "shared",
        "showReuseMessage": false,
        "clear": true
      },
      "isBackground": true,
      "problemMatcher": {
        "owner": "pants",
        "source": "pytest",
        "fileLocation": "relative",
        "background": {
          "activeOnStart": true,
          "beginsPattern": ".",
          "endsPattern": ".*Launching debug adapter.*",
        },
        "pattern": [
          {
            "regexp": ".",
            "file": 1,
            "location": 2,
            "message": 3
          }
        ]
      }
    }
  ]
}

Expected behavior

PreLaunchTask to run, and debugpy to attach to remote configuraiton

Steps to reproduce:

Above launch.json/task.json and a sample pants project

[jasondamour]

If I manually run the task, then start the debugger (with preLaunchtask commented out), then it attaches as expected.

Also, if I change localhost to 127.0.0.1 in launch.json, then I finally get an error in the popup:

connect ECONNREFUSED 127.0.0.1:5678

So maybe this is a race condition between the line being printed and pdb listening on the port?

[jasondamour]

Answering my own question a little: Pants does print that line before listening. So this is probably a race condition, and can be solved outside of debugpy.
https://github.com/pantsbuild/pants/blob/main/src/python/pants/core/goals/test.py#L868

However, it is still frustrating/confusing that vscode doesn't print connection refused when using localhost

[jasondamour]

And full circle!

Since Pants just uses debugpy under the hood and doesn't micromanage the process, it doesn't really know when the process is successfully listening. So I need debugpy to print a log line after it starts listening, that I can use in the tasks.json endPattern to trigger vscode attaching.

Is there such an option to print a log line after debugpy --wait-for-client is listening?

[jasondamour]

Here's the log line I'm looking to trigger tasks.json on: https://github.com/microsoft/debugpy/blob/main/src/debugpy/server/api.py#L276

But I need this printed to stdout...

[jasondamour]

Alright, I have my workaround:

• --log-to-stderr passed to debugpy
• In tasks.json, problemMatcher.background.endsPattern set to Adapter is accepting incoming client connections

This works and is done "the right way" without wrapper scripts, sleeps, etc. However, now debugpy is logging tons of stuff to stderr, 258 log lines at the start of every test!

Ask: Can debugpy please signal that it is successfully listening in a concise manner?

[jasondamour]

Submitted a PR for a quick fix: #1700