Show entire toctree in Read The Docs sidebar

Note: The previous answer was outdated. As @Ariel notes in a comment, the maxdepth is now configurable by setting navigation_depth in html_theme_options. As per the README, change this in your project's conf.py:

html_theme_options = {
    'navigation_depth': 4,
}

---

Looking at the source for the theme on Github, it seems the ToC depth is hard-coded on line 93 in sphinx_rtd_theme/layout.html. As such, there is no configuration you can make to the theme to override it.

Since the line is hard-coded, you will always get the global toctree returned by toctree, instead of the local one "supported" by the following lines.

You can, of course, fork the theme and change that line for your local use (and you can use custom themes on RTD so should work there as well). I tried doing so with the demo theme. It looks like this with maxdepth=3, so some additional CSS might be needed. The documentation for the toctree template function specifies that for unlimited depth, simply pass maxdepth=-1. Note that this does not add collapse/expand to the sublevels of the TOC.

Might be a good target for a pull request?