[Bug 624788] Re: dependency resolution doesn’t use its own decisions

[Rolf Leggewie]

Thank you for the thorough analysis with which I agree in principle.  Do
you have a more recent test case?

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Title:
  dependency resolution doesn’t use its own decisions

Status in aptitude package in Ubuntu:
  New

Bug description:
  Binary package hint: aptitude

  Hello! I recently encountered a problem I noticed earlier and decided
  to report it. Consider the snippet I pasted below. It’s a run of
  aptitude when I asked it to install the current version of Amarok
  (2.something), for testing. I had used until now a forked version of
  Amarok 1.4 from my own PPA. The exact packages are not particularly
  important, I’ve encountered the same behavior from aptitude, and
  worse, on other occasions. It’s the structure of the dependencies
  that’s important.

  In this case, there are packages amarok14 and amarok14-common, which
  depend on one another, and also amarok14-engine-xine. The later
  recommends amarok14 (since it’s not useful without it, but the exact
  reason is not important). amarok14 conflicts with amarok (the 2.x
  version), because it uses the same paths; this avoids the two versions
  messing each-other’s databases.

  So, what happens is that aptitude correctly notices the conflicts, and
  offers to remove amarok14, amarok14-common and amarok14-engine-xine;
  so far so good. However, it also mentions at the end “Leave the
  following dependencies unresolved: amarok14-engine-xine recommends
  amarok14”. This is incorrect: the action it proposed above would
  uninstall a...-engine-xine, so the “recommends” dependency would no
  longer be present after the removal (thus, it wouldn’t be left
  unresolved).

  At the very least, this behavior is confusing. However, I’m pretty
  sure I encountered similar behavior in the past, when the dependencies
  “left unresolved” after the removal were stronger and/or more complex,
  and aptitude seemed to be confused by them. On occasion it didn’t
  notice simple resolutions for some package conflicts, apparently
  because of this kind of issue. I’m pretty sure that its “cost”
  estimates for some resolutions are off quite a bit.

  Since aptitude’s behavior for complex updates (e.g., a distribution
  upgrade) is quite arcane in cases, I’d be surprised if this bug didn’t
  cause quite a few ugly messes. It should be fixed.

  ***********************
  bogdanb at mabelode:~$ sudo aptitude install amarok
  The following NEW packages will be installed:
    amarok amarok-common{a} amarok-utils{a} kdemultimedia-kio-plugins{a} libindicate-qt0{a} libkcddb4{a} 
    libknewstuff2-4{a} libloudmouth1-0{a} libqtscript4-core{a} libqtscript4-gui{a} libqtscript4-network{a} 
    libqtscript4-sql{a} libqtscript4-uitools{a} libqtscript4-xml{a} libtag-extras1{a} 
  0 packages upgraded, 15 newly installed, 0 to remove and 0 not upgraded.
  Need to get 13.0MB/13.2MB of archives. After unpacking 51.0MB will be used.
  The following packages have unmet dependencies:
    amarok14-common: Conflicts: amarok (>= 2:2) but 2:2.3.1-1ubuntu5 is to be installed.
                     Conflicts: amarok-common but 2:2.3.1-1ubuntu5 is to be installed.
    amarok14: Conflicts: amarok but 2:2.3.1-1ubuntu5 is to be installed.
  The following actions will resolve these dependencies:

       Remove the following packages:                                       
  1)     amarok14                                                           
  2)     amarok14-common                                                    
  3)     amarok14-engine-xine                                               

       Leave the following dependencies unresolved:                         
  4)     amarok14-engine-xine recommends amarok14 (= 2:1.4.10-0ubuntu3~ppa5)

  ProblemType: Bug
  DistroRelease: Ubuntu 10.10
  Package: aptitude 0.6.3-2ubuntu3
  ProcVersionSignature: Ubuntu 2.6.35-17.23-generic 2.6.35.2
  Uname: Linux 2.6.35-17-generic x86_64
  NonfreeKernelModules: nvidia
  Architecture: amd64
  Date: Thu Aug 26 18:55:49 2010
  EcryptfsInUse: Yes
  ProcEnviron:
   LANGUAGE=en_US:en
   PATH=(custom, user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: aptitude

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