Python extension 2024.12.3 breaks pytest discovery in Cursor (env parse error / Pixi noise)

Bug Reports
1

Summary

Running Cursor 0.49.6 on macOS arm64 with the bundled Python extension ms‑python.python 2024.12.3 (Cursor-bundled) breaks pytest discovery.
The extension crashes during startup with a JSON‑parse error and repeatedly watches a non‑existent .pixi/envs directory.

Environment

  • Python extension ms‑python.python 2024.12.3 (bundled)
Version: 0.49.6 (Universal)
VSCode Version: 1.96.2
Commit: 0781e811de386a0c5bcb07ceb259df8ff8246a50
Date: 2025-04-25T04:39:09.213Z (1 wk ago)
Electron: 34.3.4
Chromium: 132.0.6834.210
Node.js: 20.18.3
V8: 13.2.152.41-electron.0
OS: Darwin arm64 24.4.0

Steps to reproduce

  1. Open the repo in Cursor (only .venv, no pixi.toml, no .pixi/).
  2. Open the Testing view – Cursor starts “Discovering tests…”.
  3. Observe Output / Dev Tools logs:
2025-05-07 13:59:04.185 [info] Experiment 'pythonTerminalEnvVarActivation' is inactive
2025-05-07 13:59:04.185 [info] Experiment 'pythonDiscoveryUsingWorkers' is inactive
2025-05-07 13:59:04.185 [error] Reading directory to watch failed [Error: ENOENT: no such file or directory, scandir '~/Desktop/repos/my-repo/.pixi/envs'
	at Object.readdirSync (node:fs:1507:26)
	at t.readdirSync (node:electron/js2c/node_init:2:13703)
	at ~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/out/client/extension.js:2:586747
	at ~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/out/client/extension.js:2:586938
	at Array.map (<anonymous>)
	at d.initWatchers (~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/out/client/extension.js:2:586656)
	at async d.ensureWatchersReady (~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/out/client/extension.js:2:543067)] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'scandir',
  path: '~/Desktop/repos/my-repo/.pixi/envs'
}
2025-05-07 13:59:04.186 [error] Dir "~/Desktop/repos/my-repo/.pixi/envs" is not watchable (directory does not exist)
2025-05-07 13:59:04.186 [info] Default formatter is set to ms-python.black-formatter for workspace ~/Desktop/repos/my-repo
2025-05-07 13:59:04.186 [info] VS Code was launched from an activated environment: '.venv', selecting it as the interpreter for workspace.
2025-05-07 13:59:04.186 [info] Python interpreter path: ./.venv/bin/python
2025-05-07 13:59:04.209 [info] > pyenv which python
2025-05-07 13:59:04.209 [info] cwd: .
2025-05-07 13:59:06.347 [info] Starting Pylance language server.
2025-05-07 14:31:04.981 [info] Discover tests for workspace name: my-repo - uri: ~/Desktop/repos/my-repo
2025-05-07 14:31:04.995 [info] > pixi --version
2025-05-07 14:31:05.010 [error] [Error: spawn pixi ENOENT
	at ChildProcess._handle.onexit (node:internal/child_process:285:19)
	at onErrorNT (node:internal/child_process:483:16)
	at process.processTicksAndRejections (node:internal/process/task_queues:82:21)] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'spawn pixi',
  path: 'pixi',
  spawnargs: [ '--version' ]
}
2025-05-07 14:31:05.011 [warning] could not find a pixi interpreter for the interpreter at ~/Desktop/repos/my-repo/.venv/bin/python
2025-05-07 14:31:05.024 [info] > . ./.venv/bin/activate && echo 'e8b39361-0157-4923-80e1-22d70d46dee6' && python ~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/python_files/printEnvVariables.py
2025-05-07 14:31:05.024 [info] shell: bash
2025-05-07 14:31:05.209 [warning] could not find a pixi interpreter for the interpreter at ~/Desktop/repos/my-repo/.venv/bin/python
2025-05-07 14:31:05.210 [info] > ./.venv/bin/python ~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/python_files/testing_tools/run_adapter.py discover pytest -- --rootdir . -s --cache-clear tests
2025-05-07 14:31:05.210 [info] cwd: .
2025-05-07 14:31:10.246 [error] Error discovering pytest tests:
 [n [Error]: sys:1: DeprecationWarning: builtin type swigvarlink has no __module__ attribute

	at ChildProcess.<anonymous> (~/.cursor/extensions/ms-python.python-2024.12.3-darwin-arm64/out/client/extension.js:2:228920)
	at Object.onceWrapper (node:events:633:26)
	at ChildProcess.emit (node:events:518:28)
	at maybeClose (node:internal/child_process:1104:16)
	at ChildProcess._handle.onexit (node:internal/child_process:304:5)
	at Process.callbackTrampoline (node:internal/async_hooks:130:17)]
  1. Test explorer stays empty; individual tests cannot be debug‑run either.

Expected behaviour

  • Python extension starts without errors.
  • Pytest discovery lists tests, identical to VS Code (same workspace + extension 2025.4.0).

Actual behaviour

  • Extension crashes while parsing environment variables, so test discovery never completes.
  • Continuous ENOENT warnings for .pixi/envs although Pixi isn’t used in the project.

Root‑cause summary

  • 2024.12.3 always watches .pixi/envs, generating ENOENT noise when Pixi isn’t present.
  • The "pythonTerminalEnvVarActivation" experiment runs an env‑collector script whose output is not valid JSON when large multiline variables are present; the resulting SyntaxError aborts extension activation, killing pytest discovery.
  • Up‑stream fixes:
    • PR #24319 — watcher now activates only if pixi.toml exists.
    • Issue #23604 — env‑collector JSON bug was refactored; according to upstream reports, this is no longer an issue in 2025.x.

Note: I haven’t personally tested with 2025.x inside Cursor yet (can’t sideload), but this bug no longer occurs in standard VS Code with 2025.x.