Hi Ludo,

> But precisely: as Alexander wrote, when JUPYTER_CONFIG_DIR points to the
> store, jupyterlab cannot drop a config file there.  Or am I missing
> something?
sorry, my message was unclear here. The config file is written at
build time.

> BTW, if JUPYTER_CONFIG_DIR is meant to contain a directory name, as
> opposed to a colon-separated search path, we should make this change:
Looking at the documentation[1] again this is correct, but I feel we
should use JUPYTER_CONFIG_PATH instead, because it supports
colon-delimited entries, see attached patch. However that does not get
rid of error messages like these, when trying to use Settings→JupyterLab
Theme for example:

[W 08:10:14.476 LabApp] 500 PUT /lab/api/workspaces/lab?1639383014500 (127.0.0.1): [Errno 30] Read-only file system: '/gnu/store/8q7wdpdddfqh46plbbsa3rwci5092n5y-profile/etc/jupyter/lab'

So it seems that JUPYTER_CONFIG_PATH overrides the default
JUPYTER_CONFIG_DIR, when the latter is not set. Or maybe guix-science’s
jupyterlab is simply too old – not sure right now.

Cheers,
Lars

[1] https://jupyter.readthedocs.io/en/latest/use/jupyter-directories.html