Failure: The 3.0 solver produced a worse result: libcanberra-gtk3-0t64 fails to upgrade

[Alan Chia]

Desktop popup saying system problem.

ProblemType: AptSolver
DistroRelease: Ubuntu 25.04
Package: apt 2.9.30ubuntu1
ProcVersionSignature: Ubuntu 6.12.0-15.15-generic 6.12.11
Uname: Linux 6.12.0-15-generic x86_64
ApportVersion: 2.31.0+git20250220-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
Date: Tue Feb 25 14:20:51 2025
ErrorMessage:

InstallationDate: Installed on 2024-04-03 (328 days ago)
InstallationMedia: Ubuntu 22.04.4 LTS "Jammy Jellyfish" - Release amd64 (20240220)
SourcePackage: apt
Title: Failure: The 3.0 solver produced a worse result
UpgradeStatus: No upgrade log present (probably fresh install)

[Julian Andres Klode (juliank)]

This has been fixed already over the last month.

[Julian Andres Klode (juliank)]

Actually it wasn't, this dump simply is too old and affected by other bugs in the dumper. It seems this was the result of an `apt upgrade` but the old version did not differentiate and rendr it the same as an `apt-get upgrade`, in turn forbidding packages from being installed.

In any case I can reproduce the bug and it is sort of correct.

[Julian Andres Klode (juliank)]

# Problem statement

The problem here is that

* Installed gnome-settings-daemon Depends: libcannbera-gtk3-0
* Installed libcanberra-gtk3-0t64 (= 0.30-10ubuntu10) Provides: libcanberra-gtk3-0
* Upgrade libcanberra-gtk3-0t64 (= 0.30-17ubuntu2) Depends: libcanberra-gtk3-0

i.e. we renamed libcanberra-gtk3-0 to libcanberra-gtk3-0t64 in noble and then back in plucky.

The solver now resolves that by expanding
  gnome-settings-daemon Depends: libcannbera-gtk3-0
to
  gnome-settings-daemon Depends: libcanberra-gtk3-0t64 (= 0.30-10ubuntu1) | libcannbera-gtk3-0 (= new version)

i.e. it prefers libcanberra-gtk3-0t64 because that is already installed. But since the new version dropped the Provides, only the old version is a valid solution.

Now when visiting the dependencies, it sees that dependency, and solves it by picking the first choice, that is keeping the old version.

# Solutions

There are two solutions to this particular instance:

(1) The upgrade for libcanberra-gtk3-0t64 is Section: olddlibs. We should not prefer oldlibs packages over other packages, that is, the dependency should have expanded to libcannbera-gtk3-0 (= new version) | libcanberra-gtk3-0t64 (= 0.30-10ubuntu1).

(2) The more complex general case is disappeared provides: If the candidate lost the Provides that satisfied the dependency before, we should consider the old version to be an "obsolete Provider", that is,
libcanberra-gtk3-0t64 is obsolete wrt providing libcannbera-gtk3-0.

I have locally implemented solution (1), but it stands to reason that (2) should be implemented too. A test case can be constructed for (2) by taking the test case for (1) and changing the section from oldlibs to something "not obsolete".