[Bug 831768] Re: aptitude cannot handle conflicts with multiarch enabled

[Tim]

I have tested the precise patch in combination with my  ppa-purge  patch
(Bug #892886), and everything seems to be working smoothly as far as
purging packages on a multiarch precise system now.

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Title:
  aptitude cannot handle conflicts with multiarch enabled

Status in aptitude:
  Fix Released
Status in “aptitude” package in Ubuntu:
  Fix Released
Status in “aptitude” source package in Oneiric:
  Confirmed
Status in “aptitude” source package in Precise:
  Confirmed
Status in Baltix GNU/Linux:
  Incomplete
Status in “aptitude” package in Debian:
  Fix Released

Bug description:
  [Impact]

  * Inability to use aptitude on multi-arch systems.  Any action which
  results in a packaging conflict, or otherwise broken package, invokes
  the problem resolver which will proceed to remove *all* foreign-arch
  packages.

  The packages are removed always, even if they are unrelated to the
  problem being resolved.  In the usual case, the problem resolver is
  unable to find any solution which does not involve removing all
  foreign-arch packages.

  * Complete lack of upstream support for aptitude, regardless of
  whether any specific issue appears to be related to multi-arch.

  Upstream does not provide any support for aptitude where it is installed on a multi-arch system unless all of these conditions are met:
  - it is at least version 0.6.6; and
  - attached multiarch-conflicts.patch is applied.

  At this point Ubuntu is 100% provider of support for aptitude on
  Oneiric, and Precise.

  [Fix]

  As attached.  Update the problem resolver to be more informed about multi-arch packages and specifically the implicit package relations associated
  with them.

  [Test Case]
  1. Enable multiarch (should be automatic on new oneiric systems)
  2. Install an i386 package on amd64 (like flashplugin-installer:i386)
  3. Mark something with a lot of dependencies for installation
  4. On the confirmation screen, try to remove on of the dependencies (aptitude will now fail to perform upgrades when there's a package conflict w/out removing the i386 libs)

  This renders aptitude painful on a multiarch enabled system (default
  in oneiric).

  [Workaround]
  1. If you can survive without 32 bit libraries, just comment out the single line in /etc/dpkg/dpkg.cfg.d/multiarch; or
  2. Use another package manager (e.g. apt-get, synaptic, or Software Center)
  3. Disable the problem resolver by adding this line in /etc/apt/apt.conf:

  Aptitude::ProblemResolver::StepLimit "0";

  [Regression Potential]

  * Patch is of moderate size but requires someone with strong APT
  knowledge to verify.

  * Some package relations, particularly conflicts and breaks, may be
  wrongly ignored and packages not identified as broken by aptitude.
  This can leave a system in a broken state and/or result in dpkg
  errors.

  * Any complex dependency situation is potentially handled incorrectly.

  * Already in Wheezy, Sid, and Quantal.  No regressions reported.

  * Multiple user confirmations that the patch works on aptitude 0.6.6.

  ** Do not even consider applying this patch to SRU without it being
  first thoroughly inspected by a seasoned APT person.  If you have
  never looked deep in to the workings of, say, class pkgProblemResolver
  (libapt-pkg) or the aptitude problem resolver, then you are probably
  underqualified to inspect the patch. **

  * None of the regression potential has any consideration given to
  Ubuntu-specific factors.  An Ubuntu dev. should consider reviewing and
  updating as appropriate, at least to remove this notice.

  [Original Report]
  ProblemType: Bug
  DistroRelease: Ubuntu 11.10
  Package: aptitude 0.6.4-1ubuntu2
  Architecture: amd64

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