[Bug 2067071] Re: cannot upgrade from 23.10 to 24.04, error in _install_t64_replacement_packages

[Lupe Christoph]

I tried an upgrade myself and it failed like before. I checked and just
like Owen described, it ran release-upgrader 24.04.18.

I had 24.04.19 installed and this added to the normal /etc/apt:

/etc/apt/sources.list.d/noble-proposed.list
deb http://de.archive.ubuntu.com/ubuntu/ noble-proposed multiverse restricted universe main

/etc/apt/preferences.d/proposed-updates
Package: ubuntu-release-upgrader*
Pin: release a=noble-proposed
Pin-Priority: 700

No use. At an early stage of do-release-upgrade apt-cache complained
about this. And since there is a noble-proposed.list.distUpgrade left
behind I assume that the upgrade process disabled noble-proposed.list.
Just great!

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Title:
  cannot upgrade from 23.10 to 24.04, error in
  _install_t64_replacement_packages

Status in ubuntu-release-upgrader package in Ubuntu:
  Invalid
Status in ubuntu-release-upgrader source package in Noble:
  Fix Committed

Bug description:
  [Impact]

  Upgrades to Noble may crash while searching for t64 replacement
  packages.

  [Test Plan]

  One way to reproduce this is by setting Pin-Priority: -1 for a t64
  replacement package so that `replacement` will have no candidate.

  $ apt install -y libts0
  $ cat > /etc/apt/preferences.d/lp2067071  << EOF
  Package: libts0t64
  Pin: release a=noble
  Pin-Priority: -1
  EOF
  $ do-release-upgrade

  Before the patch, that will lead to the same crash shown in this bug
  report.

  [Where problems could occur]

  The patch is confined to the t64 replacement quirk. Any other issues
  would be there. The fix is to simply make sure the replacement has a
  candidate (i.e. replacement.candidate is not None) before accessing
  more attributes.

  [Original Description]

  it crashes while calculating space - cannot proceed to package
  downloading.

  short from the logs:

  File "/tmp/ubuntu-release-upgrader-4lhpwkx7/DistUpgrade/DistUpgradeCache.py", line 497, in pre_upgrade_rule
      self.quirks.run("PreDistUpgradeCache")
    File "/tmp/ubuntu-release-upgrader-4lhpwkx7/DistUpgrade/DistUpgradeQuirks.py", line 95, in run
      func()
    File "/tmp/ubuntu-release-upgrader-4lhpwkx7/DistUpgrade/DistUpgradeQuirks.py", line 191, in PreDistUpgradeCache
      self._install_t64_replacement_packages()
    File "/tmp/ubuntu-release-upgrader-4lhpwkx7/DistUpgrade/DistUpgradeQuirks.py", line 1845, in _install_t64_replacement_packages
      if replacement.candidate._cand != ver:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  AttributeError: 'NoneType' object has no attribute '_cand'

  full logs attached as files.

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