[Bug 1916725] Re: Protected/Important packages are not deconfigured, require Force-LoopBreak

[Julian Andres Klode]

** Description changed:

  [Impact]
  If a package that is Protected: yes (or Important: yes), or one of it's dependencies, is involved in a dependency loop with Breaks, APT requires APT::Force-LoopBreak instead of resolving the situation directly.
+ 
+ On focal, we also introduce the actual support for protected packages to
+ enable upgrading to later releases more easily (in case a protected
+ package needs to be removed during the upgrade), and to make the
+ backport more similar to main.
  
  [Test plan]
  Run the integration test suite (the autopkgtest) :)
  
  Our test suite covers the tests for both Breaks and Conflicts.
  
  Breaks:
  
  protected-sysvinit (= 1) without dependencies is installed
  protected-sysvinit (= 2) Pre-Depends protected-systemd-sysv
  protected-systemd-sysv (= 2) Breaks: protected-sysvinit (<< 2)
  
  Test: Install protected-sysvinit (= 2)
  Expected result: Unpacking protected-sysvinit (= 2) deconfigures protected-sysvinit (= 1), and then we unpack and configure protected-sysvinit (= 2) and end up with a working system.
  
  Conflicts: As for Breaks, but the Conflicts will remove the package
  temporarily, requiring the use of APT::Force-LoopBreak option.
  
+ For focal, we also do have a test to check that the Protected field is
+ being used.
+ 
  [Where problems could occur]
  We now allow dpkg to automatically deconfigure protected packages. This should just make them behave like normal packages to APT's eye, but bugs I guess could occur somewhere in the APT/dpkg interaction (this only applies to releases with Protected support in dpkg, Important is not affected, it's always been "normal" for dpkg).
  
  During development, we accidentally simplified the patch so much that
  Conflicts did not require Force-LoopBreak for temporary removal. We
  fixed that, but it points out that there is a place where the loop break
  check happens that is a potential regression place.
+ 
+ On focal, we pass additional flags to dpkg that focal's dpkg does not
+ understand, however, we only do that if dpkg asserts it does that, so in
+ practice, this should all work fine and the code path will only be taken
+ with >=groovy dpkg.

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https://bugs.launchpad.net/bugs/1916725

Title:
  Protected/Important packages are not deconfigured, require Force-
  LoopBreak

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Bionic:
  Triaged
Status in apt source package in Focal:
  Triaged
Status in apt source package in Groovy:
  In Progress
Status in apt source package in Hirsute:
  Fix Released

Bug description:
  [Impact]
  If a package that is Protected: yes (or Important: yes), or one of it's dependencies, is involved in a dependency loop with Breaks, APT requires APT::Force-LoopBreak instead of resolving the situation directly.

  On focal, we also introduce the actual support for protected packages
  to enable upgrading to later releases more easily (in case a protected
  package needs to be removed during the upgrade), and to make the
  backport more similar to main.

  [Test plan]
  Run the integration test suite (the autopkgtest) :)

  Our test suite covers the tests for both Breaks and Conflicts.

  Breaks:

  protected-sysvinit (= 1) without dependencies is installed
  protected-sysvinit (= 2) Pre-Depends protected-systemd-sysv
  protected-systemd-sysv (= 2) Breaks: protected-sysvinit (<< 2)

  Test: Install protected-sysvinit (= 2)
  Expected result: Unpacking protected-sysvinit (= 2) deconfigures protected-sysvinit (= 1), and then we unpack and configure protected-sysvinit (= 2) and end up with a working system.

  Conflicts: As for Breaks, but the Conflicts will remove the package
  temporarily, requiring the use of APT::Force-LoopBreak option.

  For focal, we also do have a test to check that the Protected field is
  being used.

  [Where problems could occur]
  We now allow dpkg to automatically deconfigure protected packages. This should just make them behave like normal packages to APT's eye, but bugs I guess could occur somewhere in the APT/dpkg interaction (this only applies to releases with Protected support in dpkg, Important is not affected, it's always been "normal" for dpkg).

  During development, we accidentally simplified the patch so much that
  Conflicts did not require Force-LoopBreak for temporary removal. We
  fixed that, but it points out that there is a place where the loop
  break check happens that is a potential regression place.

  On focal, we pass additional flags to dpkg that focal's dpkg does not
  understand, however, we only do that if dpkg asserts it does that, so
  in practice, this should all work fine and the code path will only be
  taken with >=groovy dpkg.

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