Error when used with Jupyter Book: source_suffix '.ipynb' is already registered

[psychemedia]

Running this extension with Jupyter Book (a custom sphinx build), which already has ipynb registered as a file type, generates an error when building a book:

Extension error:
source_suffix '.ipynb' is already registered

Also described here: jupyter-book/jupyter-book#1344 (comment)

Offending line is presumably:

jupyterlite-sphinx/src/jupyterlite_sphinx.py

Line 274 in f14181a

app.add_source_suffix(".ipynb", "jupyterlite_notebook")

[martinRenou]

Thanks for reporting. I wonder what should be done for fixing this.

We could either use the override option (see https://www.sphinx-doc.org/en/master/extdev/appapi.html#sphinx.application.Sphinx.add_source_suffix) to force using jupyterlite-sphinx suffix handlers, or we could back off if it's already registered.

I guess the second option is best. The end user can override that in their configuration anyway (see https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-source_suffix).

So maybe something like

try:
    app.add_source_suffix(".ipynb", "jupyterlite_notebook")
except ExtensionError:
    # Show a warning explaining how to force "jupyterlite_notebook"?
    pass

[psychemedia]

Yeah, I was wondering if there was a way of looking up already registered source suffixes, other than raising an exception if you try to re-add one, but I can't spot anything from a quick look at the docs.

The override option is new to me (I wonder if there are any side effects from re-registering a suffix?).

[martinRenou]

, I was wondering if there was a way of looking up already registered source suffixes

Looking at the Sphinx code, we could probably do:

if '.ipynb' not in self.app.registry.source_suffix:
    app.add_source_suffix(".ipynb", "jupyterlite_notebook")
else:
    # Show a warning explaining how to force "jupyterlite_notebook"?
    pass

The override option is new to me (I wonder if there are any side effects from re-registering a suffix?).

I guess the side-effect there would be that if you're already using jupyter-sphinx or nbpshinx then those extensions would not work as expected anymore.

[martinRenou]

We can also probably do just like nbsphinx does https://github.com/spatialaudio/nbsphinx/blob/64cd5a4ddadc8fb03887f3fac821cdfd184d6246/src/nbsphinx.py#L1889-L1890

[martinRenou]

Actually what nbsphinx does does not work and collide with jupyterlite-sphinx, so I guess my proposition above is safer.