[Bug 1887544] Re: upgrade from 18.04 to 20.04 fails to calculate if python-dbg is installed

[Michał Margula]

** Attachment added: "main.log"
   https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1887544/+attachment/5421012/+files/main.log

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https://bugs.launchpad.net/bugs/1887544

Title:
  upgrade from 18.04 to 20.04 fails to calculate if python-dbg is
  installed

Status in ubuntu-release-upgrader package in Ubuntu:
  Fix Released
Status in ubuntu-release-upgrader source package in Focal:
  Fix Committed

Bug description:
  Impact
  ------
  Users with the package python-dbg installed on their system are unable to upgrade from Ubuntu 18.04 LTS to Ubuntu 20.04 LTS as the upgrade path is not calculable. Additionally, other python packages from Ubuntu 18.04 will be left installed or removed when they should not be.

  Test Case
  ---------
  [python-dbg]
  1) On an Ubuntu 18.04 LTS system install python-dbg (or some set of packages which depend on it)
  2) Run do-release-upgrade
  3) Observe a message regarding a failure to calculate the upgrade

  With the dist-upgrader from -proposed there will be no such failure to
  calculate the upgrade.

  [python-doc]
  1) On an Ubuntu 18.04 LTS system install python-doc
  2) Run do-release-upgrade
  3) Say Y to removing obsolete packages
  4) Observe that python-doc is still installed on the system

  With the version of the dist-upgrader from -proposed python-doc will
  not be installed after the upgrade and python2-doc will be.

  [python-dev]
  1) On an Ubuntu 18.04 LTS system install python-dev
  2) Run do-release-upgrade
  3) Say Y to removing obsolete packages
  4) Observe that python-dev is still installed on the system

  With the version of the dist-ugprader from -proposed python-dev will
  not be installed after the upgrade and python2-dev will be installed.
  Additionally, python-dev-is-python2 will be installed.

  Regression Potential
  --------------------
  The logic of the "_install_python_is_python2" quirk is essentially the same but the set of replacements is being expanded so we should ensure that this does not cause any additional package removals which may are unwanted.

  Original Description
  --------------------
  the problem is during issue  this command from terminal to start upgrade
  process from 18.04 to 20.04

  $cat /etc/lsb-release

  DISTRIB_ID=Ubuntu
  DISTRIB_RELEASE=18.04
  DISTRIB_CODENAME=bionic
  DISTRIB_DESCRIPTION="Ubuntu 18.04.4 LTS"

  $ uname -mrs

  Linux 5.3.0-62-generic x86_64

  Using this command
  sudo do-release-upgrade -d
  this is the output

  [sudo] password for amr:
  Checking for a new Ubuntu release
  Get:1 Upgrade tool signature [1,554 B]
  Get:2 Upgrade tool [1,342 kB]
  Fetched 1,343 kB in 6s (211 kB/s)
  authenticate 'focal.tar.gz' against 'focal.tar.gz.gpg'
  extracting 'focal.tar.gz'

  Reading cache

  Checking package manager
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  Hit http://archive.ubuntu.com/ubuntu bionic InRelease
  Get:1 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
  Get:2 http://archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
  Get:3 http://archive.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
  Get:4 http://archive.ubuntu.com/ubuntu bionic-security/main amd64 Packages [783 kB]
  Get:5 http://archive.ubuntu.com/ubuntu bionic-security/main i386 Packages [506 kB]
  Get:6 http://archive.ubuntu.com/ubuntu bionic-security/universe amd64 Packages [679 kB]
  Get:7 http://archive.ubuntu.com/ubuntu bionic-security/universe i386 Packages [625 kB]
  Fetched 2,845 kB in 6s (15.3 kB/s)
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done

  Checking for installed snaps

  Calculating snap size requirements

  Updating repository information
  Hit http://archive.ubuntu.com/ubuntu focal InRelease
  Hit http://archive.ubuntu.com/ubuntu focal-updates InRelease
  Hit http://archive.ubuntu.com/ubuntu focal-backports InRelease
  Hit http://archive.ubuntu.com/ubuntu focal-security InRelease
  Fetched 0 B in 6s (0 B/s)

  Checking package manager
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done

  Calculating the changes

  Calculating the changes

  Could not calculate the upgrade

  An unresolvable problem occurred while calculating the upgrade.

  This was caused by:
  * Upgrading to a pre-release version of Ubuntu
  This is most likely a transient problem,
  please try again later.
  If none of this applies, then please report this bug using the
  command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If
  you want to investigate this yourself the log files in
  '/var/log/dist-upgrade' will contain details about the upgrade.
  Specifically, look at 'main.log' and 'apt.log'.

  Restoring original system state

  Aborting
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done

  ProblemType: BugDistroRelease: Ubuntu 18.04
  Package: ubuntu-release-upgrader-core 1:18.04.37
  ProcVersionSignature: Ubuntu 5.3.0-62.56~18.04.1-generic 5.3.18
  Uname: Linux 5.3.0-62-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.15
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: ubuntu:GNOME
  Date: Tue Jul 14 17:08:10 2020
  InstallationDate: Installed on 2020-02-27 (137 days ago)
  InstallationMedia: Ubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
  PackageArchitecture: allSourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to bionic on 2020-07-14 (0 days ago)

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