Include subheadings in navigation tree

[amyreese]

Describe the solution you'd like
Pages in my index toctree (with maxdepth > 1) should include subheadings in the navigation menu, similar to alabaster. Having this as optional behavior would be fine, as long as it's available to me. I've written longer pages, and would like the navigation tree to make it easier to jump to the right section without having to first go to that page, then click to expand the content menu, then click on the section.

Describe alternatives you've considered
Tried adding explicit toctree entries, but that does not work for linking to headings/anchors rather than documents, and the only other alternative is making more documents, but that seems like overkill, especially for things like autodoc content.

Additional context
Building docs for aioitertools: https://github.com/omnilib/aioitertools/tree/main/docs

index.rst includes api.rst in a toctree with maxdepth 2. alabaster includes the subheadings from api.rst in the nav tree, but furo doesn't.

With alabaster:

With furo:

[pradyunsg]

Thanks for filing this issue!

I'm not going to be adding this since separating the "page structure" from "site structure" in Furo, is an explicit design choice. The left sidebar is for presenting site structure and the right sidebar is for presenting the page content hierarchy. I find the mixing of the two in other Sphinx themes to be a suboptimal experience when looking for information.

[rlaphoenix]

It seems you have since implemented this on your own documentation for Furo, but I see no way of activating it.

[amyreese]

Those are shown because they are subpages, ie, TOC within the customisation/index.md page that was included in the main index.md page.

[pradyunsg]

See #318 (comment).