Integrated subproject sites on readthedocs.org

This has been bothering me for a few years now, but in the FAQ for readthedocs it calls out the celery/kombu projects as an example of subprojects on RTD. And.. ok, I suppose it’s technically true, they are related projects, and they do use the subprojects. But if you didn’t know that kombu existed, you’d never be able to find it from the celery project. But they aren’t good examples, and as far as I can tell, no large project uses subprojects in an integrated/useful/obvious way.

Until I did it in December, anyways.

Now, one problem RobotPy has had is that we have a lot of subprojects. There’s robotpy-wpilib, pynetworktables, the utilities library, pyfrc… and until recently each one had it’s own unique documentation site, and there was some duplication of information between site. But it’s annoying, because you have to search all of these projects to find what you want, and it was difficult to discover new related content across projects.

However, I’m using subprojects on RTD now, and all of the subproject sites now share a unified sidebar that make them seem to be one giant project. There are a few things that make this work:

  • automatically generate the sidebar, which means the toctree in all of the documentation subproject sites are the same.
  • They use intersphinx to link between the sites
  • But more importantly, the intersphinx links and the sidebar links are all generated based on whether not the project is ‘stable’ or ‘latest’.

The last point is really the most important part and requires you to be a bit disciplined. You don’t want your ‘latest’ documentation subproject pointing to the ‘stable’ subproject, or vice versa — chances are if the user selected one or the other, they want to stay on that through all of your sites. Thankfully, detecting the version of the site is pretty easy:

# on_rtd is whether we are on readthedocs.org, this line of code grabbed from docs.readthedocs.org
on_rtd = os.environ.get('READTHEDOCS', None) == 'True'

# This is used for linking and such so we link to the thing we're building
rtd_version = os.environ.get('READTHEDOCS_VERSION', 'latest')
if rtd_version not in ['stable', 'latest']:
    rtd_version = 'stable'

Then the intersphinx links are generated:

intersphinx_mapping = {
  'robotpy': ('http://robotpy.readthedocs.io/en/%s/' % rtd_version, None),
  'wpilib': ('http://robotpy-wpilib.readthedocs.io/en/%s/' % rtd_version, None),
}

And  as a result, they point to the correct version of the remote sites, as do the sidebar links.

While this approach may not work well for everyone, it has worked really well for the RobotPy project. Feel free to use this technique on your sites, and check out the RobotPy documentation site at robotpy.readthedocs.io!

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