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Bug#780443: apt: fails to compute upgrade path for plymouth-themes-all



Control: reassign -1 plymouth

On Fri, Mar 13, 2015 at 11:51:09PM +0100, Andreas Beckmann wrote:
> I recently started doing piuparts wheezy->jessie upgrade tests that
> upgrade apt first and then have apt from jessie perform the reminder of
> the upgrade. Unexpectedly I found a regression: while apt/wheezy could
> do a smooth upgrade for plymouth-themes-all, this failed with
> apt/jessie. The two piuparts logs with problemresolver debugging enabled
> are attached.

Failing (apt/jessie):
>  Investigating (0) plymouth [ amd64 ] < 0.8.5.1-5 -> 0.9.0-9 > ( misc )
>  Broken plymouth:amd64 Breaks on plymouth-drm [ amd64 ] < 0.8.5.1-5 > ( misc ) (< 0.9.0-6~)
>    Considering plymouth-drm:amd64 3 as a solution to plymouth:amd64 3
>    Holding Back plymouth:amd64 rather than change plymouth-drm:amd64

Successful (apt/wheezy):
>  Investigating (0) plymouth [ amd64 ] < 0.8.5.1-5 -> 0.9.0-9 > ( misc )
>  Broken plymouth:amd64 Breaks on plymouth-drm [ amd64 ] < 0.8.5.1-5 > ( misc ) (< 0.9.0-6~)
>    Considering plymouth-drm:amd64 5 as a solution to plymouth:amd64 6
>    Added plymouth-drm:amd64 to the remove list
>    Fixing plymouth:amd64 via remove of plymouth-drm:amd64

The important part is the 3 vs 3 (first) or 5 vs 6 (second) scoring.

The scoring calculation changed slightly, which accounts for the diff
(effective negative dependencies give a -1 score now, which is why both
 have a lower score now).

What has to be realized here is that this is a pretty fragile transition
in any version – a single point is easily achieved e.g. by the user
still having wheezy sources enabled while upgrading to jessie – given
that plymouth-drm has a bunch of dependencies (themes) in wheezy which
need to be dropped as well which gives plymouth-drm all these points.


I would recommend making plymouth-drm an empty transitional package
depending on plymouth. Maybe make it Breaks the themes packages as well.
Either way, the themes-packages are leaf enough to be dropable (they
have a -1 at the moment). The -all Has a score of 2, but that comes from
the recommends from plymouth-drm (1 point for the recommends itself and
points plymouth-drm got awarded directly along this recommends).
So even if the user has still wheezy sources or other small point
fluctuations we should be save.


This is a lot cleaner from a user-point of view as well as in
a dist-upgrade where thousands of packages are touched it is easy to
miss that plymouth isn't actually completely removed (and even if the
user sees it, its still not clear if this set provides the same level
of features as before if you aren't an expert). If all packages removed
are 'themes' you can at least guess that everything will be fine.


I am not bumping to release critical as if you follow the release notes
to the letter everything is "fine", but I would treat it as such as not
everyone does.

Best regards

David Kalnischkies

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