[Bug 2111742] Re: 3.0 solver inadvertently removes packages during install

[Launchpad Bug Tracker]

This bug was fixed in the package apt - 3.1.0ubuntu3

---------------
apt (3.1.0ubuntu3) questing; urgency=medium

  * solver3: Only merge dependencies on the same package

 -- Julian Andres Klode <juliank at ubuntu.com>  Wed, 28 May 2025 14:34:31
+0200

** Changed in: apt (Ubuntu Questing)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/2111742

Title:
  3.0 solver inadvertently removes packages during install

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Plucky:
  Triaged
Status in apt source package in Questing:
  Fix Released

Bug description:
  [Impact]
  The solver evaluation revealed cases where installing new packages inadvertently removed manually installed packages from the system such as ubuntu-minimal.

  For users on the default solver, this causes two issues:

  1. If the default solver fails to find a solution, it may fall back to
  the new solver and present the inadvertent solution.

  2. If the solution is not presented, but worse, and a report filed
  with errors.ubuntu.com

  For users using the 3.0 solver explicitly, for example, using the
  `--solver 3.0` argument or setting `APT::Solver "3.0"` in apt.conf,
  the issue only has an effect if the option `APT::Solver::RemoveManual`
  is set to `1`, which is not the default case.

  [Test plan]
  Replay the APT solver dump

  https://errors.ubuntu.com/oops/1b55173a-3526-11f0-b7ac-fa163e171f02
  https://errors.ubuntu.com/oops/dbd5149e-36b9-11f0-bb74-fa163ec44ecd

  And ensure that no manual package is being removed.

  To replay the solver dump:

  Pass the AptSolverDump value through

    base64 -d | zstd -d | /usr/lib/apt/solvers/solver3 -o
  APT::Solver::RemoveManual=1

  and ensure that the problem can be resolved without removing any
  packages, that is,

  1. The output ends with Message: Done
  2. The output contains no Remove: lines

  To further analyse the output the analyse-edsp.py tool from the edsp test suite may be helpful:
    https://salsa.debian.org/apt-team/apt-tests/-/tree/main?ref_type=heads

  [Where problems could occur]
  Problems could occur for users who manually use `--solver 3.0` if the new assumption mechanism or the changes to enable it contain errors - it may
  fail to find a solution where it did before, for example.

  For default users, this may cause additional slow downs or reports to
  be generated for cases where no reports where previously generated (or
  in the worst case apt segfaulting).

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