Bug#677407: gnome-dbg: fails to upgrade from squeeze - apt does not find an upgrade path

[Simon McVittie]

On Sat, 16 Jun 2012 at 10:49:19 +0200, Andreas Beckmann wrote:
> the problem I previously reported for gnome-dbg now also shows up for
> gnome-core.

Your log from 1st November is for gnome-dbg. Is this reproducible
for gnome-core too, or only for gnome-dbg?

Could you please explain how an apt or GNOME developer with no particular
knowledge of piuparts or pbuilder can reproduce this upgrade issue? (I
use sbuild for my package uploads, so I don't have a working pbuilder
setup; in his message of 13th October, Neil Williams performed a
"realistic" upgrade test of gnome-dbg in a Squeeze virtual machine,
which was successful.)

On Thu, 01 Nov 2012 at 23:04:52 +0100, Andreas Beckmann wrote:
> Still reproducible in squeeze->wheezy upgrades, new logfile with
> problemresolver debug output attached.

The problems still seem to start here:

>   Investigating (0) gir1.2-gstreamer-0.10 [ amd64 ] < none -> 0.10.36-1 > ( introspection )
>   Broken gir1.2-gstreamer-0.10:amd64 Conflicts on gir1.0-gstreamer-0.10 [ amd64 ] < 0.10.30-1 > ( libs )
>     Considering gir1.0-gstreamer-0.10:amd64 1 as a solution to gir1.2-gstreamer-0.10:amd64 1
>     Holding Back gir1.2-gstreamer-0.10:amd64 rather than change gir1.0-gstreamer-0.10:amd64

That's not the answer we want: apt should be willing
to remove gir1.0-gstreamer-0.10:amd64. Unfortunately,
gir1.0-gstreamer-0.10 and gir1.2-gstreamer-0.10 both have a score of 1,
and apt seems to tie-break in the wrong direction.

>   Broken libseed-gtk3-0:amd64 Depends on gir1.2-gstreamer-0.10 [ amd64 ] < none -> 0.10.36-1 > ( introspection )
>     Considering gir1.2-gstreamer-0.10:amd64 1 as a solution to libseed-gtk3-0:amd64 5
>     Holding Back libseed-gtk3-0:amd64 rather than change gir1.2-gstreamer-0.10:amd64

This is the result of the above; that breaks libpeas, which breaks
various applications.

Would an artificial dependency, gnome-dbg Depends: gir1.2-gstreamer-0.10
or even gnome-core Depends: gir1.2-gstreamer-0.10, perhaps reassure apt that it
was doing the right thing by installing gir1.2-gstreamer-0.10 and
dropping gir1.0-gstreamer-0.10? Or is there something else that src:meta-gnome
could do to hint apt to do the right thing?

I call this dependency "artificial" because gnome-core has no particular
reason to depend on a random GIR file; but if doing so for the wheezy
release would help the upgrade, it would be fairly harmless to do so, because
they're already related by these chains:

  gnome-core Depends: gnome-sushi Depends: gir1.2-gstreamer-0.10
  gnome-core D: eog D: libpeas-1.0-0 D: libseed-gtk3-0 D: gir1.2-gstreamer-0.10

Perhaps another way to convince apt to DTRT would be to change the
dependency

  libseed-gtk3-0 D: gir1.2-gstreamer-0.10 | libgstreamer0.10-0 (< 0.10.25-3)

and remove the obsolete alternative (the second branch), to make the
"right answer" more obvious?

Regards,
    S