removal of priority changed packages breaks builds of the core snap

The image fails to build because we attempt to remove the systemd-sysv from the system. We do this because there is a newer version of systemd-sysv in an applied PPA for this build and that version is marked as Priority: important.

  $ apt-cache show systemd-sysv | egrep Priority\|Version
  Priority: important
  Version: 229-4ubuntu16+ppa2
  Priority: required
  Version: 229-4ubuntu16
  Priority: required
  Version: 229-4ubuntu10
  Priority: required
  Version: 229-4ubuntu4
  $

This leads us to attempt to remove the package. The removal only deletes that one package so it is deemed removable and all hell breaks loose. The removal of this package triggers a pile of installations of new packages presumably for dependencies with alternatives which are satisfiable. In this case with a complete switch to upstart.

I believe there are two main bugs in this code. Firstly we should only be taking into account the latest version available for Priority: detection; otherwise we could switch a package back to required and it would still be removed (though in this case the removal is valid based on priority). Secondly we should not be only considering removals when testing the apt-get remove we should also consider whether its removal triggers installation of new packages; this latter implies there is a dependency but an alternative could be found.

Potential (untested) debdiff to fix these two issues. It almost cirtainly should be merged with the base patch and not applied as is.

Hello Oliver, or anyone else affected,

Accepted live-build into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/live-build/3.0~a57-1ubuntu25.3 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

This bug was fixed in the package live-build - 3.0~a57-1ubuntu29

---------------
live-build (3.0~a57-1ubuntu29) zesty; urgency=medium

  * Drop ubuntu-debootstrap-demotions.patch, this should have been a
    one-time hack for xenial demotions, not a feature (LP: #1678042)

 -- Adam Conrad <email address hidden> Fri, 31 Mar 2017 05:52:24 -0600

Oliver, I believe we can release this to xenial-updates as soon as you verify that an ubuntu-core build with -proposed enabled works with this change.

long done :)

This bug was fixed in the package live-build - 3.0~a57-1ubuntu25.3

---------------
live-build (3.0~a57-1ubuntu25.3) xenial; urgency=medium

  * ubuntu-debootstrap-demotions.patch: Hard-code the removals instead of
    trying to play fancy games with detection of demotions (LP: #1678042)

 -- Adam Conrad <email address hidden> Fri, 31 Mar 2017 05:30:01 -0600

The verification of the Stable Release Update for live-build has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.