Assign tuple to list slice (sys.path[:]) causes problem in pypy

[Alkaid-Benetnash]

Environment data

• VS Code version: 1.55.2
• Extension version (available under the Extensions sidebar): v2021.3.680753044
• OS and version: archlinux 5.11.13
• Python version (& distribution if applicable, e.g. Anaconda): pypy3 (based on Python 3.7.10, PyPy 7.3.4)
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): N/A
• Relevant/affected Python packages and their versions: N/A
• Relevant/affected Python-related VS Code extensions and their versions: N/A
• Value of the python.languageServer setting: jedi

Expected behaviour

vscode-python can recognize the pypy3 as a valid interpreter.

Actual behaviour

It reports "The Python path in your debug configuration is invalid".
The status bar also indicates "select python interpreter" (even if I already specified one in settings.json).

Steps to reproduce:

1. Install pypy3 (i.e. pacman -S pypy3 in archlinux)
2. Select pypy3 as the python interpreter

Logs

I already triaged the problem to be

cd ${HOME}/.vscode/extensions/ms-python.python-2021.3.680753044/pythonFiles
pypy3 pyvsc-run-isolated.py interpreterInfo.py
# has the error ModuleNotFoundError: No module named 'json'

The reason is this line. The sys.path[:] is assigned to be a tuple, which somehow makes sys.path an empty list. I don't understand why a tuple is assigned to a list slice, nor why pypy3 behaves like this.

Changing this line to:
sys.path[:] = [p for p in sys.path if p != "" and normalize(p) != cwd]
solved the problem.

[olliemath]

Can confirm, I also ran into this issue with the latest pypy on Ubuntu 20.04

The suggested change fixed it for me. I've attached a PR.

[olliemath]

Also, it's not a tuple, but a generator.

I guess that foo[:] = some_generator_from(foo) has undefined behaviour at the language level (you're saying "please lazily evaluate this generator from foo while simultaneously changing the stuff inside foo"). Python already has safety rails for this with some other types (if you've ever seen "x changed size during iteration" you'll know what I mean).

[karthiknadig]

@Alkaid-Benetnash @olliemath Set this in your settings to turn off isolation. "python.useIsolation" = false