Created attachment 430990 [details]
Build fails with Can't load file: Unrecognized image file format when tools is not specified as use flag for gnome-base/librsvg
Also see https://forums.gentoo.org/viewtopic-t-1007524-view-next.html
After some discussion, [tools] is likely not necessary
So gtk+:3 now ships with a gtk-encode-symbolic-svg, which converts a SVG into a special PNG for faster loading, but supposedly it still is scalable in some special ways or something.
This encoding likely needs to be able to read SVG via gdk-pixbuf, so probably needs librsvg.
This means technically gtk+:3 should rdepend on librsvg, but that's not really acceptable. So we have two choices:
1) gtk-encode-symbolic-svg (build time) using packages need librsvg in DEPEND
2) we split gtk-encode-symbolic-svg to a separate package that RDEPENDs on librsvg too, and packages using gtk-encode-symbolic-svg need to add it to DEPEND
Not sure many other icon themes are even using this yet (or shipping symbolic icnos).
Easiest to just do 1) for adwaita-icon-theme now and contemplate 2) for the long-term.
While this could be a problem for fresh installs when librsvg is pulled in after adwaita-icon-theme (because it's only in RDEPEND, not DEPEND), Kristian says he likely had librsvg already there due to in one case it being an upgrade of adwaita-icon-theme instead.
I'm adding librsvg and gtk+:3 to build depend to (initially masked) adwaita-icon-theme-3.24 for gtk-encode-symbolic-svg to be able to do its work. I hope it doesn't introduce any circular dependencies that way.
I'm not sure how many other themes ship symbolic icons and want to generate the PNG versions during build, but we should review and at least add the librsvg/gtk+ build deps there too or something. And maybe to adwaita-icon-theme-3.22 too.
Here is some information about the gtk-encode-symbolic-svg utility (it's basically a performance tool for symbolic icons in the common case with gtk+ making use of its results to achieve the perf gain):
This utility loads a symbolic svg at a specified size and renders a png file in a special format that can be recolored later.
Is this still a thing?