Gtkmm4 documentation not installed

I’ve been developing gtkmm4 apps for awhile now, but I recently needed ot look for some documentation so naturally I installed gnome.devhelp, but even in a nix-shell (run with nix-shell -p gtkmm4), no gtkmm4 docs appear. Am I doing anything wrong and is there a way that I can install the documentation?

We are currently not building docs for all packages. Mostly because nobody bothered to add them yet. I try to add docs when refactoring a package but haven’t gotten to gtkmm yet.

But you can try to do that yourself. In most cases it should be as simple as adding "devdoc" to outputs attribute, and gtk-doc, libxslt and docbook-xsl-nons to nativeBuildInputs (example). You will then be able to test it by running env XDG_DATA_DIRS=$(nix-build -A gtkmm4.devdoc)/share devhelp. Then you can open a Nixpkgs pull request.