[Bug 1945205] [NEW] [FFe] Add zstd support

[Athos Ribeiro]

Public bug reported:

[Feature Freeze Exception]

Now that dpkg-deb defaults to compressing with zstd, python-debian can
no longer decompress the compressed data into the binary package archive
[1].

The proposed change, created as an MP at [2], introduces zstd support to
python-debian 0.1.39 by adding a dependency to zstd to the package and
by extending the python-debian xz support for python < 3.3, where xz was
still not supported by tarfile, to also support the zstd compression.

It is also important to note that, for python-debian 0.1.40, the
relevant (here patched) code was re-worked (python < 3.3 support was
dropped) and this proposed patch, along with the relevant proposed unit
test, will need to be re-written. This re-writing effort is already an
ongoing work proposed upstream in [3].

Once [3] is merged, this patch can be dropped and python-debian can be
sync'd from upstream again. If there is a need to merge python-debian
before [3] is accepted and released upstream, the next version of
python-debian will need to drop the proposed patch and apply [3]
instead, for the reasons listed above.

While python-debian is not completely broken without this FFe patch,
some of its features will not work properly on Ubuntu packages now they
are compressed with zstd. For instance, any packages or scripts that try
to use python-debian for extracting data from deb packages will no
longer work. Namely, dh-cmake FTBFS when trying to decompress a deb
package during its unit test run step [4].

A PPA with the proposed fix is available at [5], along with the build
logs.

I ran the dep8 test suite locally with the following results:

  autopkgtest [20:04:02]: @@@@@@@@@@@@@@@@@@@@ summary
  python3-debian PASS

I am also attaching the logs for installation, removal and upgrades of
the patched package.

[1] https://bugs.launchpad.net/ubuntu/+source/python-debian/+bug/1923845
[2] https://code.launchpad.net/~athos-ribeiro/ubuntu/+source/python-debian/+git/python-debian/+merge/407413
[3] https://salsa.debian.org/python-debian-team/python-debian/-/merge_requests/65
[4] https://launchpadlibrarian.net/552708462/buildlog_ubuntu-impish-amd64.dh-cmake_0.6.1_BUILDING.txt.gz
[5] https://launchpad.net/~athos-ribeiro/+archive/ubuntu/lp-1923845-python-debian/+packages

** Affects: python-debian (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "intall, remove, and upgrade logs"
   https://bugs.launchpad.net/bugs/1945205/+attachment/5528416/+files/python-debian_install_remove_upgrade.txt

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https://bugs.launchpad.net/bugs/1945205

Title:
   [FFe] Add zstd support

Status in python-debian package in Ubuntu:
  New

Bug description:
  [Feature Freeze Exception]

  Now that dpkg-deb defaults to compressing with zstd, python-debian can
  no longer decompress the compressed data into the binary package
  archive [1].

  The proposed change, created as an MP at [2], introduces zstd support
  to python-debian 0.1.39 by adding a dependency to zstd to the package
  and by extending the python-debian xz support for python < 3.3, where
  xz was still not supported by tarfile, to also support the zstd
  compression.

  It is also important to note that, for python-debian 0.1.40, the
  relevant (here patched) code was re-worked (python < 3.3 support was
  dropped) and this proposed patch, along with the relevant proposed
  unit test, will need to be re-written. This re-writing effort is
  already an ongoing work proposed upstream in [3].

  Once [3] is merged, this patch can be dropped and python-debian can be
  sync'd from upstream again. If there is a need to merge python-debian
  before [3] is accepted and released upstream, the next version of
  python-debian will need to drop the proposed patch and apply [3]
  instead, for the reasons listed above.

  While python-debian is not completely broken without this FFe patch,
  some of its features will not work properly on Ubuntu packages now
  they are compressed with zstd. For instance, any packages or scripts
  that try to use python-debian for extracting data from deb packages
  will no longer work. Namely, dh-cmake FTBFS when trying to decompress
  a deb package during its unit test run step [4].

  A PPA with the proposed fix is available at [5], along with the build
  logs.

  I ran the dep8 test suite locally with the following results:

    autopkgtest [20:04:02]: @@@@@@@@@@@@@@@@@@@@ summary
    python3-debian PASS

  I am also attaching the logs for installation, removal and upgrades of
  the patched package.

  [1] https://bugs.launchpad.net/ubuntu/+source/python-debian/+bug/1923845
  [2] https://code.launchpad.net/~athos-ribeiro/ubuntu/+source/python-debian/+git/python-debian/+merge/407413
  [3] https://salsa.debian.org/python-debian-team/python-debian/-/merge_requests/65
  [4] https://launchpadlibrarian.net/552708462/buildlog_ubuntu-impish-amd64.dh-cmake_0.6.1_BUILDING.txt.gz
  [5] https://launchpad.net/~athos-ribeiro/+archive/ubuntu/lp-1923845-python-debian/+packages

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