Virtualenv 20: Jupyter Kernels not detected

[nils-werner]

Prerequisites

• Have you checked the solutions in our troubleshooting guide for common problems ?
• Have you checked that your issue isn't already filed ?

Description

When creating an environment using virtualenv >= 20, Hydrogen is unable to automatically pick up Kernels available in the environment. This used to work just fine with virtualenv < 20.

Steps to Reproduce

To reproduce this we need four environments:

1. oldvenv, created by system-virtualenv, with virtualenv<20 inside
2. newvenv, created by system-virtualenv, with virtualenv>=20 inside
3. venv16, created by virtualenv<20 from environment 1, with Jupyter inside
4. venv20, created by virtualenv>=20 from environment 2, with Jupyter inside

virtualenv oldvenv
oldvenv/bin/pip install "virtualenv < 20"
virtualenv newvenv
newvenv/bin/pip install "virtualenv >= 20"

oldvenv/bin/virtualenv --version
oldvenv/bin/virtualenv venv16

newvenv/bin/virtualenv --version
newvenv/bin/virtualenv venv20

venv16/bin/pip install jupyter
venv20/bin/pip install jupyter

source venv16/bin/activate
atom .
# run some Python script, Kernels are detected

deactivate
source venv20/bin/activate
atom .
# run some Python script, Kernels are not detected

Versions

OS version:
Arch Linux latest

atom --version

Atom    : 1.45.0
Electron: 4.2.12
Chrome  : 69.0.3497.128
Node    : 10.11.0

apm --version

apm  2.4.5
npm  6.14.4
node 13.13.0 x64
atom 1.45.0
python 3.8.2
git 2.26.1

Hydrogen version:

2.14.1

Plugins

Have you installed and activated any of the Hydrogen plugins below ?

• hydrogen-python
• Hydrogen Launcher
• Data Explorer

Logs

There is only findCodeBlock and CellManager content in the logs, they are unrelated to Kernel detection.

Expected behavior

I expect Hydrogen to pick up Kernels in environments created by both virtualenv<20 and virtualenv>=20.

[nils-werner]

I started looking into how venv16 and venv20 differ and I noticed that Virtualenv 20 creates python as a symlink to the system-wide python, and Virtualenv 16 doesn't.

ls -alh venv16/bin/python
# -rwxr-xr-x 1 nils nils 14K 16. Apr 10:13 venv16/bin/python*
ls -alh venv20/bin/python
# lrwxrwxrwx 1 nils nils  18 16. Apr 10:13 venv20/bin/python -> /usr/bin/python3.8*

If I create the virtualenv using the --copies flag, no such symlink is created but the executable is instead copied:

newvenv/bin/virtualenv --copies venv20copies

venv20copies/bin/pip install jupyter

source venv20copies/bin/activate
atom .

And Kernels are successfully detected.

So it seems the Hydrogen Kernel detector is unable to deal with symlinks?

As a workaround, you may create a virtualenv config file (see the last line of virtualenv --help for the location of that file) with the contents

[virtualenv]
copies = True