[Bug 1894919] Re: gnome-software-plugin-snap consider an unwanted removal for 20.04 ubuntu-desktop

[Brian Murray]

** Description changed:

  [Impact]
  Many packages are not considered for removal by the release upgrader when upgrading from bionic to focal because gnome-software-plugin-snap is a part of the removal set but is not itself considered for removal. However, if you run 'sudo apt autoremove' after upgrading from bionic to focal you will have a lot of packages which will be auto removed.
  
  [Test Case]
  1) Upgrade an 18.04 system with ubuntu-desktop installed to Ubuntu 20.04 (do-release-upgrade -d)
  2) At the end of the upgrade choose to remove unneeded packages
  3) When the upgrade has finished run 'sudo apt autoremove' and observe that the list of packages in comment #3 are all removable.
  
  With the version of the release-upgrader from -proposed the packages
  listed in comment #3 will be removed as a part of the upgrade process
  and will not appear in the list of packages 'sudo apt autoremove' wants
  to remove.
  
  [Regression Potential]
  While this change should only affect systems with the ubuntu-desktop or ubuntu-kylindesktop metapackage installed we should also test the upgrade of a different flavor (xubuntu-desktop) which depends on gnome-software-plugin-snap to ensure that it is not removed.
+ 
+ Additionally, we should ensure that nothing extra is autoremoved by
+ collecting and comparing the list of packages installed after an upgrade
+ with and without the dist-upgrader from -proposed. We'll want to make
+ sure that only the packages that are in the 'sudo apt autoremove' list
+ are not installed on the system that used the dist-upgrader from
+ -proposed.
  
  Original Description
  --------------------
  I've been testing some release upgrades from 18.04 to 20.04 and noticed some packages were not getting removed with the following in /var/log/dist-upgrade/main.log.
  
   2020-09-07 15:57:38,148 DEBUG package 'libxml-sax-expat-perl' produces an unwanted removal 'gnome-software-plugin-snap', skipping
   2020-09-07 15:57:40,290 DEBUG 'libxml-sax-expat-perl' scheduled for remove but not safe to remove, skipping
   2020-09-07 15:57:40,349 DEBUG package 'libexporter-tiny-perl' produces an unwanted removal 'gnome-software-plugin-snap', skipping
   2020-09-07 15:57:42,485 DEBUG 'libexporter-tiny-perl' scheduled for remove but not safe to remove, skipping
  
  In Ubuntu 18.04 this package was a part of the following tasks:
  
  Task: ubuntu-desktop, xubuntu-desktop, ubuntustudio-desktop,
  ubuntukylin-desktop, ubuntu-budgie-desktop
  
  However, for 20.04 it is a part of the following tasks:
  
  Task: xubuntu-desktop, ubuntustudio-desktop, ubuntu-budgie-desktop
  
  Because the package is in main it is not a removal candidate itself but
  given that it is no longer part of the ubuntu-desktop and ubuntukylin-
  desktop packages it seems reasonable to add it to ForcedObsoletes but
  only for those 2 metapackages.

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https://bugs.launchpad.net/bugs/1894919

Title:
  gnome-software-plugin-snap consider an unwanted removal for 20.04
  ubuntu-desktop

Status in ubuntu-release-upgrader package in Ubuntu:
  Invalid
Status in ubuntu-release-upgrader source package in Focal:
  In Progress

Bug description:
  [Impact]
  Many packages are not considered for removal by the release upgrader when upgrading from bionic to focal because gnome-software-plugin-snap is a part of the removal set but is not itself considered for removal. However, if you run 'sudo apt autoremove' after upgrading from bionic to focal you will have a lot of packages which will be auto removed.

  [Test Case]
  1) Upgrade an 18.04 system with ubuntu-desktop installed to Ubuntu 20.04 (do-release-upgrade -d)
  2) At the end of the upgrade choose to remove unneeded packages
  3) When the upgrade has finished run 'sudo apt autoremove' and observe that the list of packages in comment #3 are all removable.

  With the version of the release-upgrader from -proposed the packages
  listed in comment #3 will be removed as a part of the upgrade process
  and will not appear in the list of packages 'sudo apt autoremove'
  wants to remove.

  [Regression Potential]
  While this change should only affect systems with the ubuntu-desktop or ubuntu-kylindesktop metapackage installed we should also test the upgrade of a different flavor (xubuntu-desktop) which depends on gnome-software-plugin-snap to ensure that it is not removed.

  Additionally, we should ensure that nothing extra is autoremoved by
  collecting and comparing the list of packages installed after an
  upgrade with and without the dist-upgrader from -proposed. We'll want
  to make sure that only the packages that are in the 'sudo apt
  autoremove' list are not installed on the system that used the dist-
  upgrader from -proposed.

  Original Description
  --------------------
  I've been testing some release upgrades from 18.04 to 20.04 and noticed some packages were not getting removed with the following in /var/log/dist-upgrade/main.log.

   2020-09-07 15:57:38,148 DEBUG package 'libxml-sax-expat-perl' produces an unwanted removal 'gnome-software-plugin-snap', skipping
   2020-09-07 15:57:40,290 DEBUG 'libxml-sax-expat-perl' scheduled for remove but not safe to remove, skipping
   2020-09-07 15:57:40,349 DEBUG package 'libexporter-tiny-perl' produces an unwanted removal 'gnome-software-plugin-snap', skipping
   2020-09-07 15:57:42,485 DEBUG 'libexporter-tiny-perl' scheduled for remove but not safe to remove, skipping

  In Ubuntu 18.04 this package was a part of the following tasks:

  Task: ubuntu-desktop, xubuntu-desktop, ubuntustudio-desktop,
  ubuntukylin-desktop, ubuntu-budgie-desktop

  However, for 20.04 it is a part of the following tasks:

  Task: xubuntu-desktop, ubuntustudio-desktop, ubuntu-budgie-desktop

  Because the package is in main it is not a removal candidate itself
  but given that it is no longer part of the ubuntu-desktop and
  ubuntukylin-desktop packages it seems reasonable to add it to
  ForcedObsoletes but only for those 2 metapackages.

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