[Bug 2025462] Re: Apt deletes ubuntu-desktop during dist-upgrade

[Andreas Hasenack]

I checked previous SRUs, and we do rely on the automated tests for such
changes, as it can be difficult to fabricate something "in real life"
that would remain valid for the time we need it to be. I'm glad tests
are being added.

This being a native package, and imported into the archive without rich
history, it's a bit hard to follow what was described in d/changelog and
the actual changes for a package I'm unfamiliar with, but I checked with
the upstream branch in salsa, and it looks ok.

The po/* changes, and doc changes, are just about the version, so should
be no issue for translators.

The same set of changes is applied to jammy and lunar, and in devel.

** Changed in: apt (Ubuntu Lunar)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-lunar

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Title:
  Apt deletes ubuntu-desktop during dist-upgrade

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Jammy:
  Fix Committed
Status in apt source package in Kinetic:
  Won't Fix
Status in apt source package in Lunar:
  Fix Committed
Status in apt source package in Mantic:
  Fix Released

Bug description:
  [Impact]
  gnome-shell gets removed on upgrades of gnome-shell and mutter if due to phasing we can only upgrade src:gnome-shell.

  [Test plan]
  This adds a minimal test case to the test suite that reproduced the issue and verifies the fix, test plan consists of the autopkgtests.

  [Where problems could occur]
  We could see a resurgence of bugs like LP#1990586 where the solver failed to run at all because things got too complex, however this is a bit more unlikely as we now use the by-keep resolver to handle rolling back phased updates.

  We also saw an issue with a phased update's dependencies being
  installed despite the phased update being hold back. We saw that both
  before in `apt upgrade` and with the fix for this bug, we also
  introduced it to `dist-upgrade`, but this is also fixed and tested in
  these uploads, basically we skip marking for install (which in turn
  caused me to discover we need to check a different version).

  [Other Info]
  gnome-shell Depends: gnome-shell-common (= ${binary-Version), mutter (>= matching)

  So when mutter cannot be updated due to phasing, gnome-shell becomes
  non-installable, but gnome-shell-common can be updated, so APT decided
  to remove gnome-shell and the meta packages in its infinite wisdom.

  The fix addresses this by resolving the dist-upgrade as if there were
  no phasing, and then retroactively marks phases for keep and then
  anything broken by that for keep.

  This required some restructuring because normally we'd also keep
  broken Recommends back, but here dist-upgrade may have decided that
  was ok, so we need to build an allowlist of where Recommends can be
  broken to avoid undoing unrelated changes.

  [Original bug report]

  This morning I got surprised by my laptop booting to a tty instead of
  a desktop environment. It turned out that the entire desktop
  environment was no longer present on my machine. Doing an apt install
  ubuntu-desktop-minimal resolved the issue.

  The machine had been running for a while. Looking at the apt logs, it
  looks like apt deleted ubuntu-desktop on its own during a dist-upgrade
  a couple of weeks back.

  Start-Date: 2023-06-08  14:20:46
  Commandline: apt dist-upgrade
  Requested-By: alex (1000)
  Upgrade: gnome-shell-common:amd64 (44.0-2ubuntu3, 44.1-0ubuntu1)
  Remove: gnome-shell:amd64 (44.0-2ubuntu3), ubuntu-desktop:amd64 (1.501), gdm3:amd64 (44.0-1ubuntu1), gnome-shell-extension-desktop-icons-ng:amd64 (46+really47.0.2-3), gnome-shell-extension-appindicator:amd64 (53-1), ubuntu-session:amd64 (44.0-1ubuntu1), gnome-shell-extension-manager:amd64 (0.4.0-1), gnome-shell-extension-ubuntu-dock:amd64 (79ubuntu2.23.04.1), ubuntu-desktop-minimal:amd64 (1.501)
  End-Date: 2023-06-08  14:20:48

  I'm using the following version of Ubuntu:
  Distributor ID:	Ubuntu
  Description:	Ubuntu 23.04
  Release:	23.04
  Codename:	lunar

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