gtk+2 upgrade issue

[Daniel Macks <dmacks netspace org>]

I'm a bit confused about upgrading gtk+ on some machines I manage
(fully manually built from source), especially with respect to the
cairo back-end. I currently have have gtk+2 2.6.10 (no cairo) and a
boatload of gnome libs built on top of it, and various apps that use
those libs, and my users have privately built who-knows-what linking
against all that. I want to upgrade to the latest'n'greatest
cairo-enabled gtk+2 and pango, but want to minimize breakage or
mandatory recompiling or upgrading of other things during this
process. Can I "just" upgrade those libs?

I figured "same soname, I can just upgrade the lib, no problem", but
got a bit scared/confused while reading:
  http://lists.freedesktop.org/archives/pkg-config/2005-October/000036.html

So just to clarify: will I get runtime breakage for things linked
against the old one (new gtk+2 trying to pass cairo objects up to old
libs that don't know how to handle them)?

What happens if, given a linkage chain foo -> libbar -> libqux ->
libgtk+2, I upgrade libgtk+2 and then rebuild libbar (the same old
version I had)? Will there be any cairo objects or incompatible opaque
datatypes being passed to un-rebuilt libs? I'm trying to avoid forcing
a cascade of recompiling on users who have things that are already
running (and are satisfied with the older versions), and *really*
trying to avoid a nightmare of figuring out what order to do rebuilds
or other package upgrades.

dan

-- 
Daniel Macks
dmacks netspace org
http://www.netspace.org/~dmacks