glib2 has been updated in current to glib2-2.66.0. The glib2-2.66.0 slackware package installs its own version of gtk-doc, overwriting gtk-doc as supplied by linuxdoc-tools (gtk-doc-1.32). It clones the gtk-doc git repository and installs the latest version of gtk-doc in git in order to satisfy its dependencies - evidently the version supplied by linuxdoc-tools is not new enough.

If this is to be done, should not linuxdoc-tools be updated instead? More relevantly, are the two versions of gtk-doc compatible - the git version seems intended to support gtk4?

Thanks for the report. We'll look into it.

One thing that can be done is for the slackbuild to remove all the gtk-doc stuff in the glib2 slackware package, except the glib2 documentation in /usr/share/gtk-doc/html. The installation of the updated gtk-doc version by the glib2 tarball seems completely unnecessary - it is only needed in order to build the documentation, not to view it.

The version of gtk-doc bundled with linuxdoc-tools is also the most recent release, and I've built glib2 without the bundled GTK on ARM: it works fine and seems to have built its documentation without any issues.

Well whatever, you don't want slackware's gtk-doc installation to be provided by both the linuxdoc-tools and glib2 packages.

The proximate cause of that occuring with slackware's glib-2.66.0 as built for x86 (I cannot speak for ARM) is that glib-2.66.0 does not recognize the gtk-doc version supplied by linuxdoc-tools as the version it requires (you will see that the meson build is looking for gtk-doc version 1.32.1). So if you are right that the gtk-doc version supplied by linuxdoc-tools is sufficiently recent, one solution is to amend its gtk-doc.pc by hand to claim that it is at version 1.32.1. Another option is not to build the glib documentation in the first place (pass -Dgtk_doc=false to meson when building glib-2.66.0). But I should have thought the best solution is to exclude the gtk-doc implementation from slackware's glib2-2.66.0 package by amending the Slackbuild to only include the built html.

I am surprised that building glib-2.66.0 for ARM with linuxdoc-tools builds the documentation without installing a duplicated gtk-doc implementation, whereas the glib-2.66.0 slackware packages for x86/64 do duplicate it. That seems odd. Perhaps your ARM Slackbuild is different from the x86/64 one in the slackware distribution? Or maybe your ARM build is still at glib-2.64.5?

That's what I've done.

I meant that the gtk-doc stuff is now absent from the glib2 package, and that the documentation within the glib2 package seems sufficient.
The bundled gtk-doc in the latest glib2 doesn't build on ARM anyway, and as you say, it shouldn't be within the glib2 package anyway; so I'm calling it good for ARM.
I've raised it with Patrick to see how he wants to fix it for x86/64.
I should have a look at whether the linuxdoc-tools package needs an update soon as well.