dispatch PANDOC_OPTIONS base on input extensions

[ickc]

Summary

Currently, COMPILERS only has a key pandoc, and PANDOC_OPTIONS is set for all the extensions specified there. The proposed feature simply suggests to have configurable dispatch logic to allow multiple extensions calling pandoc with a different set of PANDOC_OPTIONS.

Example use case

My personal use for this would be to convert one of my site currently using .md and .markdown to mean a different target format. Both will be converted to HTML, but one of them is slideshow, another is normal "article"/post.

Another possible use case is, if one want to specify markdown extensions in pandoc, say -t markdown+...-..., then COMPILERS['pandoc'] = ['.rst', '.md'] won't work with PANDOC_OPTIONS = ['-t', 'markdown+...-...'] because that would be wrong input format for .rst.

Suggested implementation

Probably the natural way is to promote

PANDOC_OPTIONS: Union[list, Dict[str, list]]

where the keys are those in COMPILERS['pandoc'].

If it makes sense I can send a PR doing that. It seems that it only requires changes in https://github.com/getnikola/nikola/blob/master/nikola/plugins/compile/pandoc.py#L52-L56, is it true?

[Kwpolska]

Please implement this. No changes other than pandoc.py should be necessary.

[ickc]

There's one thing I don't understand and missed last time I looked:

self.config_dependencies = [str(site.config['PANDOC_OPTIONS'])]

What's this self.config_dependencies doing here? Turning it into a string is strange here. Is it just for something like logging?

[Kwpolska]

self.config_dependencies is used to figure out if a post needs updating due to config changes. PANDOC_OPTIONS should be placed there — maybe doing it directly (without str) would work. It’s easy to test: if it doesn’t work, you’d (a) get an exception, (b) fail to get a rebuild when you change PANDOC_OPTIONS, (c) get a rebuild when you didn’t change anything (run nikola build twice+ in a row to test).

[ickc]

I'll leave that alone then as it is working well in the PR. (Good to know it is watching changes from conf.py though I find that sometimes changes in conf.py is not propagated when using nikola auto.)

[Kwpolska]

changes in conf.py is not propagated when using nikola auto.

This could be a bug — please report it (we will need specific details about what you’re changing, in what cases does it work, and if it happens with nikola build; $EDITOR conf.py; nikola build)

[ickc]

I'll watch out for that in the future. Thanks.