Add hook to run arbitrary commands on save of a notebook.

[grst]

I propose to add an option that allows to execute an arbitrary command
on the notebook on every save. This would solve

• text-based notebook formats (Support for editing Plain text files (like Python, MyST and R Markdown-based) as notebooks vscode-jupyter#1240, Python Markdown extension for VS Code vscode-jupyter#1655) by running jupytext on every save;
• autoformatting (Can't use the formatter in the ipynb cell  vscode-jupyter#1221) by running, e.g. black-nb,

and has probably even more use-cases.

[rchiodo]

Thanks for the suggestion. I believe this should already be possible (at least in insiders)?

See this here:
https://code.visualstudio.com/updates/v1_23#_run-code-actions-on-save

[grst]

Thanks for the hint!

I'm not sure if I fully understood the concept of a codeAction, though. To use that feature, would I have to create a vscode extension that provides such a codeAction?

I thought of something simpler, that just pipes the entire file through a command line tool on each save.

[rchiodo]

Actually it seems the code actions are rather limited. I can't get anything to actually happen on save.

[rchiodo]

I believe this would have to be handled by VS code now as we don't get called for save anymore.