libgtk-3-bin provides gtk-encode-symbolic-svg. This program works by
loading an SVG icon and generating a PNG from it. Loading of the SVG
is done by the gdk-pixbuf, and the SVG loader is provided by
librsvg2-common. IMO, libgtk-3-bin should have a full dependency on
librsvg2-common since one of the programs it provides is entirely
non-functional without it.

Hello,

I just got bit by this upgrading a custom package from Buster to
Bullseye, where the old provider for gtk-encode-symbolic-svg
(gtk-3-examples) did somehow bring the required loader, while the new
libgtk-3-bin does not.

I agree with Dan that given this totally breaks one of the tools this
package provides it should be fixed with a plain Depends.

Anyway, for the moment I fixed my package by simply adding the
dependency manually, just like I depend on libsrvg2-bin for
imagemagick's `convert` SVG support, but that one makes more sense as
it's merely one of the many formats the `convert` tool supports.

- Colomban