[Bug 2100247] Re: Failure: The 3.0 solver produced a worse result

[Julian Andres Klode]

Action items:

(1) Fix the EDSP protocol handler to not consider a non-downloadable
version as downloadable. Funny trickery.

(2) I see postgresql-client-16 is manually installed.

The answer here seems to be that when we go look at dependencies to
process:

  postgresql-client  as postgresql-client-16 | postgresql-client | postgresqcl-client-17 | ...
             instead of postgresql-client | postgresqcl-client-17 | ... | postgresql-client-16
 
(i.e. keep the installed version as the primary choice, despite it being obsolete; because it is manually installed)

However when comparing different dependencies, e.g. a.

Depends: postgresql-client (>= 17) and Depends: postgresql-client

which would expand to
    postgresql-client | postgresqcl-client-17
    postgresql-client-16 | postgresql-client | postgresqcl-client-17 | ..

that we process the dependency mentioning obsolete packages later.

This should approximately result in the correct behavior. A manually
installed package is preserved, even if obsolete, unless something else
needs a newer version (assuming we see "something else" early enough).

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https://bugs.launchpad.net/bugs/2100247

Title:
  Failure: The 3.0 solver produced a worse result

Status in apt package in Ubuntu:
  Triaged

Bug description:
  this happens all the time when I run "apt dist-upgrade" and some
  packages are there to be installed.

  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
  NonfreeKernelModules: zfs
  ApportVersion: 2.31.0+git20250220-0ubuntu2
  Architecture: amd64
  CasperMD5CheckResult: pass
  Date: Wed Feb 26 07:18:31 2025
  ErrorMessage:
   
  InstallationDate: Installed on 2024-07-18 (223 days ago)
  InstallationMedia: Ubuntu 24.04 LTS "Noble Numbat" - Release amd64 (20240424)
  SourcePackage: apt
  Title: Failure: The 3.0 solver produced a worse result
  UpgradeStatus: Upgraded to plucky on 2024-12-20 (68 days ago)

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