[Bug 1771894] Re: /usr/bin/update-manager:TypeError:<lambda>:on_button_install_clicked:start_install:_start_pane:start:unwind_generator

[Balint Reczey]

Marking the bug as invalid for later releases because we don't exercise
this code upgrade path in later releases and in later releases lazy
loading of the backend code is fixed in LP: #1795898.

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https://bugs.launchpad.net/bugs/1771894

Title:
  /usr/bin/update-
  manager:TypeError:<lambda>:on_button_install_clicked:start_install:_start_pane:start:unwind_generator

Status in update-manager package in Ubuntu:
  Invalid
Status in update-manager source package in Xenial:
  Fix Committed

Bug description:
  [Impact]

  The backend API change made update-manager crash when the updated
  incompatible backend was loaded to the not updated running update-
  manager process.

  The issue causes crashes upon update-manager updates harming the
  upgrade experience for users.

  The fix avoids lazy loading of the backend modules but still honors
  the backend selection options.

  [Test Case]


  1. Start with a fully upgraded system and downgrade a few packages to let u-m upgrade them and also downgrade update-manager to 1:16.04.12 or earlier:
  $ sudo eatmydata apt install -y --allow-downgrades gnome-software=3.28.1-0ubuntu4 gnome-software-common=3.28.1-0ubuntu4
  $ sudo apt install update-manager=1:16.04.12 update-manager-core=1:16.04.12 python3-update-manager=1:16.04.12

  2. Start u-m with:
   $ update-manager --no-update

  3. Upgrade update-manager to a still not fixed version to observe the crash:
  $ sudo apt install update-manager=1:16.04.14 update-manager-core=1:16.04.14 python3-update-manager=1:16.04.14

  ... or to the fixed version to a see the crash not happening in step
  4:

  $ sudo apt install update-manager=1:16.04.15 update-manager-
  core=1:16.04.15 python3-update-manager=1:16.04.15

  
  4. Press "Install Now" on u-m GUI.
   The fixed u-m will successfully perform the installation, the unfixed one will fail with:
  TypeError: commit() missing 1 required positional argument: 'pkgs_remove'

  [Regression Potential]

  The change to the backend API could cause u-m not able to remove
  unused kernels, but in my testing this feature still worked.

  [Original Bug Text]

  The Ubuntu Error Tracker has been receiving reports about a problem regarding update-manager.  This problem was most recently seen with package version 1:18.04.11, the problem page at https://errors.ubuntu.com/problem/310b9890e139c17b61faeee8f50078909283794e contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
  If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.

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