Load template-related config from JSON file.

[mkcor]

Check this out, @maartenbreddels!

It's basically a cleaner version of #326 (which I will close). Still missing a test or two though...

I have used os.path.dirname to go one directory up.

Here, we are not simply reading whatever conf.json file we may find in a list of template paths, we are ensuring it corresponds to the template being used.

Demo style:

• if no conf.json file lives in PREFIX/share/jupyter/voila/templates/reveal, then running

$ voila reveal.ipynb --template=reveal

will launch a slideshow where transitions slide (because 'slide' is the default, as set in the reveal template);

• if this conf.json file lives in PREFIX/share/jupyter/voila/templates/reveal, then running

$ voila reveal.ipynb --template=reveal

will launch a slideshow where transitions zoom, because this config file is well-formed and says "transition": "zoom";

• if this conf.json file lives in PREFIX/share/jupyter/voila/templates/reveal, then running

$ voila reveal.ipynb --template=reveal --VoilaConfiguration.resources="{'reveal': {'transition': 'fade'}}"

will launch a slideshow where transitions fade, because CLI config has preference; if conf.json specified a non-default resource (e.g., "scroll": true), it wouldn't be taken into account, unfortunately, because traitlets' Config merge is not recursive...

If we really wanted to merge all template-related configs recursively, always ensuring CLI priority, we would need to have the convoluted approach I had in #326.

The little contortions I had to do in handler.py come from covering all cases, e.g., for

$ voila reveal.ipynb --template=reveal --VoilaConfiguration.resources="{'reveal': {'transition': 'fade'}}"

to run regardless, with or without a config file somewhere. And all the config merging and passing around happening in app.py leads to the fact that: a) we need to get to self.voila_configuration.config.VoilaConfiguration.resources to find those extra resources (so painfully retrieved and combined) and b) self.voila_configuration.config.VoilaConfiguration.resources ends up being of type traitlets.config.loader.LazyConfigValue when neither a file nor CLI config passes extra resources (maybe I could prevent this by setting self.voila_configuration.config.VoilaConfiguration.resources = {} ahead of time in app.py).

[mkcor]

@SylvainCorlay (following up on your earlier question, if I understand it better) with this hack, do you expect more than one way to pass resources at the CLI, for example something like

--VoilaConfiguration.resources="{'config': {'traitlet_configuration': {'resources': {'reveal': {'transition': 'fade'}}}}}"

in addition to

--VoilaConfiguration.resources="{'reveal': {'transition': 'fade'}}"

?

It's not trivial to find the alternative structure which would work, due to the convoluted config merge I'm doing here: https://github.com/QuantStack/voila/pull/372/files#diff-024301d95616622c19f49b8cd78d33c3R363-R367

[mkcor]

@maartenbreddels could you please review, so I can wrap up this week? Thanks!

[maartenbreddels]

Hi Marianne,

reviewing this I was wondering if we should use the JSONFileConfigLoader at all. Hope you find my review useful.

cheers,

Maarten

[SylvainCorlay]

@mkcor the test failure is not related to your PR and was in master. It should be fixed it you rebase on the current master.

[SylvainCorlay]

This looks good to me! Thanks for pushing this forward!

(I left a small comment inline).

[mkcor]

@mkcor the test failure is not related to your PR and was in master. It should be fixed it you rebase on the current master.

Thank you! Done.

[SylvainCorlay]

Thanks @mkcor !