Jupyterlab4 port of the extension

[mwouts]

Will close mwouts/jupytext#1054

[jtpio]

Thanks @mwouts for working on this!

While investigating Jupytext support in Notebook 7 (jupyter/notebook#6914) it appears that the toolbar is missing when opening a markdown file with the Jupytext Notebook factory (but not with the Notebook factory), in both JupyterLab and Notebook 7: jupyter/notebook#6923 (comment)

default-viewers-jupytext-jupyterlab.mp4

[mwouts]

Hey @jtpio , thank you for pointing this out! Well I am a bit clueless but I will pay attention to this, that is a strange pattern indeed.

By the way I plan to work on this issue this week-end. I think I would have a preference to continue packaging everything (I mean the Python package, the CLI, the contents manager, the server and the jupyter lab extension) in jupytext, because it makes it simpler to install - but I need to see if I can get this to work.

[jtpio]

packaging everything (I mean the Python package, the CLI, the contents manager, the server and the jupyter lab extension) in jupytext, because it makes it simpler to install

Right that makes sense 👍

[parmentelat]

I would have a preference to continue packaging everything (I mean the Python package, the CLI, the contents manager, the server and the jupyter lab extension) in jupytext

there currently are 2 different codebases for jlab3 and jlab4, and in this respect (as well as in other areas maybe) it could become a challenge

for this reason I have asked discourse to see if the community has best practices on how to deal with that
https://discourse.jupyter.org/t/jlab-extensions-that-target-both-jlab3-and-jlab4/

with these answers I can maybe propose to tweak the code of this extension to make it work with both jlab3 and jlab4, if that's helpful

[parmentelat]

for the record, the issue mentioned above by @jtpio - missing toolbar in the juptext notebook widget - is also the topic of mwouts/jupytext#1107 and fixed in mwouts/jupytext#1109

[mwouts]

Closing this PR as I am going to archive this repository (for the second time 😄)

We will continue to provide the extension in Jupytext. Starting from jupytext==1.15.0, thanks to @parmentelat , the extension will be compatible with both JupyterLab 3 and JupyterLab 4.