[Bug 1843076] Re: [eoan regression] Clicking install button no longer works in update-manager

[Łukasz Zemczak]

This is indeed an issue introduced by the latest u-r-u changes. It it
not a bug in ubuntu-release-upgrader code per-se though, it's all
because of how weirdly update-manager uses the u-r-u code. It's
astonishing that update-manager creates a MyCache class that inherits
from DistUpgradeCache.MyCache but actually *does not* call its
constructor, instead only initializing what the base apt.Cache
constructor would do. I'm pretty sure this is done for some purpose, but
it does feel like bad design to me. It relies on people knowing that
such a thing is happening and trusting that all of the
DistUpgradeCache.MyCache code that we use in update-manager will only
rely on members initialized by apt.Cache. It just feels *so* wrong.

Anyway, I will try working around this in u-r-u, since otherwise I would
have to backport both update-manager and ubuntu-release-upgrader to
disco (instead of just one package).

** Changed in: ubuntu-release-upgrader (Ubuntu)
       Status: Triaged => In Progress

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https://bugs.launchpad.net/bugs/1843076

Title:
  [eoan regression] Clicking install button no longer works in update-
  manager

Status in ubuntu-release-upgrader package in Ubuntu:
  In Progress
Status in update-manager package in Ubuntu:
  Triaged

Bug description:
  It would appear that the latest version of ubuntu-release-upgrader
  (1:19.10.11) causes the install button in update-manager to no longer
  work.

  steps to reproduce:
  - launch 'update manager'
  - updates are available
  - click 'install now'
  - nothing happens (ie crash with the below traceback)

  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/UpdateManager/Dialogs.py", line 118, in <lambda>
      button.connect("clicked", lambda x: callback())
    File "/usr/lib/python3/dist-packages/UpdateManager/UpdatesAvailable.py", line 848, in on_button_install_clicked
      self.cache.checkFreeSpace()
    File "/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeCache.py", line 1161, in checkFreeSpace
      ("/var", self.quirks.extra_snap_space),
  AttributeError: 'MyCache' object has no attribute 'quirks'

  eoan:
  - update-manager 1:19.04.7
  - ubuntu-release-upgrader 1:19.10.11

  Confirmed by
  https://errors.ubuntu.com/problem/94df71a401d64c84828d7e85e15fc6c4b3555b99

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