[Bug 2061190] [NEW] quirk needed for t64 library transitions in 24.04

[Steve Langasek]

*** This bug is a duplicate of bug 2061175 ***
    https://bugs.launchpad.net/bugs/2061175

Public bug reported:

As of right now, https://ubuntu-archive-team.ubuntu.com/nbs.html still
has a very long list of packages that need cleaned up before we release
24.04 LTS in 2 weeks, and none of these packages are considered
candidates for removal yet due to reverse-dependencies.

Most of these reverse-dependencies are amd64-only dependencies on
pre-t64 library packages, due to the fast and highly-parallelized
rebuild of packages in response to xz-utils.

The good news is that, because these libraries are ABI-compatible on
amd64 and declare so via Provides:, the amd64 packages are not
uninstallable if we remove these libraries.

The bad news is, on upgrade from prior releases, apt will not know to
replace the non-t64 library with the t64 library if the user has no
packages installed that depend on the t64 library name; leaving them
islanded on library versions that are installable and compatible, but
not security supported in 24.04.

In order to handle this without doing no-change rebuilds of all of those
reverse-dependencies (which we simply do not have time for before
release), Julian points out that it's possible for us to quirk things to
ensure the libraries are swapped on upgrade:

- for each installed package
  - if the package is no longer available, and there is a package which Replaces+Provides+(Conflicts|Breaks) that package, mark it for install

this should handle all of the t64 library transitions, and should also
be safe against accidentally switching users to a different
implementation of a package than the one they want to keep.

** Affects: ubuntu-release-upgrader (Ubuntu)
     Importance: Critical
     Assignee: Nick Rosbrook (enr0n)
         Status: Triaged

** Affects: ubuntu-release-upgrader (Ubuntu Noble)
     Importance: Critical
     Assignee: Nick Rosbrook (enr0n)
         Status: Triaged


** Tags: fr-7432

** Changed in: ubuntu-release-upgrader (Ubuntu)
   Importance: Undecided => Critical

** Changed in: ubuntu-release-upgrader (Ubuntu)
     Assignee: (unassigned) => Nick Rosbrook (enr0n)

** Tags added: fr-7432

** Changed in: ubuntu-release-upgrader (Ubuntu)
       Status: New => Triaged

** Also affects: ubuntu-release-upgrader (Ubuntu Noble)
   Importance: Critical
     Assignee: Nick Rosbrook (enr0n)
       Status: Triaged

** This bug has been marked a duplicate of bug 2061175
   Handle (t64) package replacements

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https://bugs.launchpad.net/bugs/2061190

Title:
  quirk needed for t64 library transitions in 24.04

Status in ubuntu-release-upgrader package in Ubuntu:
  Triaged
Status in ubuntu-release-upgrader source package in Noble:
  Triaged

Bug description:
  As of right now, https://ubuntu-archive-team.ubuntu.com/nbs.html still
  has a very long list of packages that need cleaned up before we
  release 24.04 LTS in 2 weeks, and none of these packages are
  considered candidates for removal yet due to reverse-dependencies.

  Most of these reverse-dependencies are amd64-only dependencies on
  pre-t64 library packages, due to the fast and highly-parallelized
  rebuild of packages in response to xz-utils.

  The good news is that, because these libraries are ABI-compatible on
  amd64 and declare so via Provides:, the amd64 packages are not
  uninstallable if we remove these libraries.

  The bad news is, on upgrade from prior releases, apt will not know to
  replace the non-t64 library with the t64 library if the user has no
  packages installed that depend on the t64 library name; leaving them
  islanded on library versions that are installable and compatible, but
  not security supported in 24.04.

  In order to handle this without doing no-change rebuilds of all of
  those reverse-dependencies (which we simply do not have time for
  before release), Julian points out that it's possible for us to quirk
  things to ensure the libraries are swapped on upgrade:

  - for each installed package
    - if the package is no longer available, and there is a package which Replaces+Provides+(Conflicts|Breaks) that package, mark it for install

  this should handle all of the t64 library transitions, and should also
  be safe against accidentally switching users to a different
  implementation of a package than the one they want to keep.

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