[Bug 2077358] Re: upgrades fail when package in ForcedObsoletes does not exist

[Nick Rosbrook]

** Description changed:

+ [Impact]
+ 
  With ubuntu-release-upgrader in noble-proposed, I get the following
  error when upgrading Ubuntu Desktop:
  
  2024-08-19 14:48:13,087 ERROR not handled exception:
  Traceback (most recent call last):
  
    File "/usr/lib/python3/dist-packages/apt/cache.py", line 281, in __getitem__
      # It might be excluded due to not having a version or something
  
  KeyError: 'gnome-app-install'
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
  
    File "/home/nr/24.04.22/./noble", line 8, in <module>
      sys.exit(main())
  
    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeMain.py", line 241, in main
      if app.run():
  
    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeController.py", line 2639, in run
      return self.fullUpgrade()
  
    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeController.py", line 2615, in fullUpgrade
      self.doPostUpgrade()
  
    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeController.py", line 2033, in doPostUpgrade
      if not self.cache[pkgname].marked_delete:
  
    File "/usr/lib/python3/dist-packages/apt/cache.py", line 283, in __getitem__
      raise KeyError("The cache has no package named %r" % key)
  
  KeyError: "The cache has no package named 'gnome-app-install'"
  
  This is because the new forced obsoletes code does not handle key errors
  with the cache.
+ 
+ [Test Plan]
+ 
+ The simplest way to test this is doing an upgrade of Ubuntu Desktop,
+ because the DistUpgrade.cfg has a ForceObsoletes= section for `ubuntu-
+ desktop` that contains at least one package that no longer exists in the
+ archive.
+ 
+ $ do-release-upgrade -d
+ 
+ The upgrade should succeed past the "removing obsoletes" section.
+ 
+ [Where problems could occur]
+ 
+ The patch here is to check for the package name as a key in the cache
+ before attempting to access it. Any more problems would be contained in
+ the "searching/removing obsoletes" logic.

** Changed in: ubuntu-release-upgrader (Ubuntu Noble)
   Importance: Undecided => High

** Changed in: ubuntu-release-upgrader (Ubuntu)
   Importance: Undecided => High

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

** Changed in: ubuntu-release-upgrader (Ubuntu Noble)
       Status: New => Triaged

** Changed in: ubuntu-release-upgrader (Ubuntu Noble)
     Assignee: (unassigned) => Nick Rosbrook (enr0n)

** Changed in: ubuntu-release-upgrader (Ubuntu)
     Assignee: (unassigned) => Nick Rosbrook (enr0n)

** Tags added: foundations-todo

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https://bugs.launchpad.net/bugs/2077358

Title:
  upgrades fail when package in ForcedObsoletes does not exist

Status in ubuntu-release-upgrader package in Ubuntu:
  Triaged
Status in ubuntu-release-upgrader source package in Noble:
  Triaged

Bug description:
  [Impact]

  With ubuntu-release-upgrader in noble-proposed, I get the following
  error when upgrading Ubuntu Desktop:

  2024-08-19 14:48:13,087 ERROR not handled exception:
  Traceback (most recent call last):

    File "/usr/lib/python3/dist-packages/apt/cache.py", line 281, in __getitem__
      # It might be excluded due to not having a version or something

  KeyError: 'gnome-app-install'

  During handling of the above exception, another exception occurred:

  Traceback (most recent call last):

    File "/home/nr/24.04.22/./noble", line 8, in <module>
      sys.exit(main())

    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeMain.py", line 241, in main
      if app.run():

    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeController.py", line 2639, in run
      return self.fullUpgrade()

    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeController.py", line 2615, in fullUpgrade
      self.doPostUpgrade()

    File "/home/nr/24.04.22/DistUpgrade/DistUpgradeController.py", line 2033, in doPostUpgrade
      if not self.cache[pkgname].marked_delete:

    File "/usr/lib/python3/dist-packages/apt/cache.py", line 283, in __getitem__
      raise KeyError("The cache has no package named %r" % key)

  KeyError: "The cache has no package named 'gnome-app-install'"

  This is because the new forced obsoletes code does not handle key
  errors with the cache.

  [Test Plan]

  The simplest way to test this is doing an upgrade of Ubuntu Desktop,
  because the DistUpgrade.cfg has a ForceObsoletes= section for `ubuntu-
  desktop` that contains at least one package that no longer exists in
  the archive.

  $ do-release-upgrade -d

  The upgrade should succeed past the "removing obsoletes" section.

  [Where problems could occur]

  The patch here is to check for the package name as a key in the cache
  before attempting to access it. Any more problems would be contained
  in the "searching/removing obsoletes" logic.

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