[Bug 2039873] Re: liblxc-dev was built with LXC_DEVEL=1 in Ubuntu 22.04 and later releases

[Dave Jones]

I had a little time to look over this again in my patch-pilot shift. I
agree it's almost certainly best to just get LXC_DEVEL set correctly
quickly. Andreas' suggested branch is a good start, but I agree with the
critique that the DEP-8 test should be checking the installed headers
rather than the built source. Due to this, it's probably also best if
the test is named something other than "build". Also, I agree it
shouldn't be marked "superficial".

I've pushed a few commits on top of Andreas' to another clone here,
which also fixes a build-failure on noble (lib/systemd instead of
usr/lib/systemd in d/lxc-utils.install):

https://code.launchpad.net/~waveform/ubuntu/+source/lxc/+git/lxc

I've tested the DEP-8 passes with the branch, and crucially that it
fails when the LXC_DEVEL fix is reverted (which it does). If this looks
sane to someone else, I'm happy to sponsor this into noble (and start
SRU proceedings for mantic and jammy).

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https://bugs.launchpad.net/bugs/2039873

Title:
  liblxc-dev was built with LXC_DEVEL=1 in Ubuntu 22.04 and later
  releases

Status in lxc package in Ubuntu:
  Confirmed
Status in lxc source package in Jammy:
  Confirmed
Status in lxc source package in Mantic:
  Confirmed
Status in lxc source package in Noble:
  Confirmed

Bug description:
  [ Impact ]

  LXC 5.0.0 was built with LXC_DEVEL=1 set for Jammy. But for release
  build we should have LXC_DEVEL=0.

  LXC_DEVEL is a variable that appears in the /usr/include/lxc/version.h
  and then can be (and actually it is) used by other projects to detect
  if liblxc-dev is a development build or stable.

  Having LXC_DEVEL=1 makes problems for the users who want to build projects those are depend on liblxc
  from source (for example, LXD, go-lxc: https://github.com/canonical/lxd/pull/12420).

  Q: Why it was not a problem for so long?
  A: Because LXC API was stable for a long time, but recently we have extended liblxc API (https://github.com/lxc/lxc/pull/4260) and dependant package go-lxc was updated too (https://github.com/lxc/go-lxc/pull/166).
  This change was developed properly to be backward compatible with the old versions of liblxc. But, there is a problem. If LXC_DEVEL=1 then the macro check VERSION_AT_LEAST (https://github.com/lxc/go-lxc/blob/ccae595aa49e779f7ecc9250329967aa546acd31/lxc-binding.h#L7) is disabled. That's why we should *not* have LXC_DEVEL=1 for *any* release build of LXC.

  [ Test Plan ]

  Install liblxc-dev package and check /usr/include/lxc/version.h file
  LXC_DEVEL should be 0

  [ Where problems could occur ]

  Theoretically, build of a software which depends on liblxc-dev may start to fail
  if it assumes that LXC_DEVEL is 1.

  [ Other Info ]

  -

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