[Bug 1730627] Re: xz compressed control.tar files not supported

[cleary]

@sil2100 Tested, confirmed it's fixed this bug for me - thankyou :)

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https://bugs.launchpad.net/bugs/1730627

Title:
  xz compressed control.tar files not supported

Status in dpkg package in Ubuntu:
  Fix Released
Status in dpkg source package in Precise:
  Won't Fix
Status in dpkg source package in Trusty:
  Fix Committed

Bug description:
  [impact]

  trusty dpkg fails when trying to extract a dpkg source package
  compressed using xz.  This breaks running autopkgtest from bionic with
  any and all trusty packages.

  [test case]

  on a bionic system, get any trusty source dpkg and run autopkgtest
  with it.  See comment 11 for an example.

  [regression potential]

  any changes to dpkg has the potential to break all package changes on
  the system, which obviously is a serious regression.  However, this
  specific change has been upstream for a very long time.  Any breakage
  would happen when dpkg is either building or extracting a deb.

  [other info]

  this affects debootstrap as well, as described in the original bug
  description:

  ---

  trusty's dpkg (1.17.5ubuntu5.7) cannot handle .deb files that contain
  control.tar files that are compressed using the xz compressor.

  Here's an example of such a case when trying to show the contents of a
  .deb file from bionic's repositories:

  dpkg-deb: error: archive './var/cache/apt/archives/ubuntu-
  minimal_1.406_amd64.deb' has premature member 'control.tar.xz' before
  'control.tar.gz', giving up

  This issue makes it currently impossible to create a bionic
  environment using debootstrap (currently from trusty-proposed).

  I have observed the issue on trusty, precisely on

  $ lsb_release -rd
  Description:	Ubuntu 14.04.5 LTS
  Release:	14.04

  using

  $ apt-cache policy dpkg
  dpkg:
    Installed: 1.17.5ubuntu5.7
    Candidate: 1.17.5ubuntu5.7
    Version table:
   *** 1.17.5ubuntu5.7 0
          500 mirror://mirrors.ubuntu.com/mirrors.txt/ trusty-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       1.17.5ubuntu5.6 0
          500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
       1.17.5ubuntu5 0
          500 mirror://mirrors.ubuntu.com/mirrors.txt/ trusty/main amd64 Packages

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