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

[Brian Murray]

** Description changed:

- 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.
+ [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.
  
-  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
+ [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.
+ 
+ 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.

  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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