[Bug 1842947] Re: dpkg 1.19.0.5ubuntu2.2 build did not recreate 'configure' file, losing changes in 'configure.ac'

[Dan Streetman]

After discussion with cjwatson in #ubuntu-devel, it looks like this is
just a dpkg-specific packaging/build-rules issue; by default, packages
will use dh_autoreconf, which will call autoreconf -f to force
(re)creation of the configure file.  The dpkg package has its own
debian/rules call to autoreconf, however, and it doesn't pass -f.

This has been fixed (maybe unintentionally) upstream by commit
c72f539b979a0c8647d2a6c62ee45565cd243b3d which moves the call to
autoreconf into an 'autogen' file, but also more importantly changes the
call from 'autoreconf -v -i' to 'autoreconf -f -i'.

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https://bugs.launchpad.net/bugs/1842947

Title:
  dpkg 1.19.0.5ubuntu2.2 build did not recreate 'configure' file, losing
  changes in 'configure.ac'

Status in dpkg package in Ubuntu:
  New

Bug description:
  [impact]

  dpkg at version 1.19.0.5ubuntu2 had support for zstd added:
  https://launchpad.net/ubuntu/+source/dpkg/1.19.0.5ubuntu2

  part of that change was to update the 'configure.ac' file with zstd support, e.g.:
  http://launchpadlibrarian.net/366237303/dpkg_1.19.0.5ubuntu1_1.19.0.5ubuntu2.diff.gz

  note that the 'configure' file was not updated - which *should* be ok,
  as it should be recreated from the 'configure.ac' file during build.
  For the build of that version and the next (1.19.0.5ubuntu2.1), the
  'configure' file was correctly recreated during build.

  However at version 1.19.0.5ubuntu2.2, the 'configure' file was not
  recreated during build.  Thus, dpkg was not built linked against
  libzstd.

  [test case]

  on bionic system:

  $ sudo apt install ubuntu-dev-tools
  $ pull-lp-source dpkg 1.19.0.5ubuntu2.2
  $ cd dpkg-1.19.0.5ubuntu2.2/
  $ sudo apt build-dep .
  $ dpkg-buildpackage

  and verify if dpkg-deb is linked against libzstd:
  $ ldd build-tree/dpkg-deb/dpkg-deb | grep zstd

  or extract it from the deb itself and check:
  $ dpkg-deb -x ../dpkg_1.19.0.5ubuntu2.2_amd64.deb ../deb-files
  $ ldd ../deb-files/usr/bin/dpkg-deb | grep zstd

  
  simply touching the 'configure.ac' file (to bring its timestamp newer than the 'configure' file) causes the build to work correctly:

  $ mkdir no-touch
  $ cd no-touch
  $ dpkg-source -x ~/dpkg_1.19.0.5ubuntu2.2.dsc
  $ cd dpkg-1.19.0.5ubuntu2.2/
  $ dpkg-buildpackage
  $ ldd build-tree/dpkg-deb/dpkg-deb | grep zstd
  $

  $ mkdir touch
  $ cd touch
  $ dpkg-source -x ~/dpkg_1.19.0.5ubuntu2.2.dsc
  $ cd dpkg-1.19.0.5ubuntu2.2/
  $ touch configure.ac
  $ dpkg-buildpackage
  $ ldd build-tree/dpkg-deb/dpkg-deb | grep zstd
  	libzstd.so.1 => /usr/lib/x86_64-linux-gnu/libzstd.so.1 (0x00007f8c1d8af000)

  [regression potential]

  TBD

  [other info]

  this might not be an issue specifically with dpkg itself, it could be
  an issue with debhelper and other tooling that is responsible for
  calling autoconf or autoreconf during build.  Or possibly a problem
  with the dpkg debian/rules or other related build config.

  Or, simply including the 'configure' file in the package source might
  be considered a bug, since it's an intermediate build file that really
  shouldn't be included.  However, it's included in many source
  packages, including in debian, and removing it from all of them seems
  unlikely and/or unwieldy.  Additionally, for "normal" packages that
  use quilt (i.e., aren't native), any changes to the 'configure.ac'
  file would be done with a patch, meaning the pre-build process would
  always make the 'configure.ac' file newer than the 'configure' file.

  Maybe for native packages, autoconf/autoreconf should always be called
  with -f, or maybe the 'configure' file should be removed from native
  packages.

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