[Reproducible-builds] Bug#820846: do not change the default compression level

[Antoine Beaupré]

Package: git-buildpackage
Version: 0.6.22
Severity: wishlist
Control: usertag -1 timestamp

git-buildpackage diverges from the default gzip settings. in
gbp/config.py, a default compression level is specified, overriding
GZIP environment variables or any similar sane defaults:

                 'compression-level': '9',

This makes git-buildpackage needlessly differ from upstream tarballs
(e.g. those created on Github). An example, with the tuptime package:

-gzip compressed data, from Unix
+gzip compressed data, max compression, from Unix

To reproduce this:

wget https://github.com/rfrail3/tuptime/archive/3.3.0.tar.gz
git clone https://github.com/anarcat/tuptime
cd tuptime
git-buildpackage

This will create a new tarball in ../tuptime_3.3.0.orig.tar.gz that
will use maximal compression whereas the tarball created on github
uses a more reasonable default compression (-6).

git-buildpackage correctly uses the -n flag to make the archive
reproducible otherwise, so one has to wonder why there is this
needless override, by default. if packages want maximum compression,
they can specify that option in gbp.conf!

(tagged as timestamp for reproducible builds, but it's not really a
timestamp, it's just the closest tag i could find)

-- System Information:
Debian Release: 8.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'proposed-updates'), (500, 'stable'), (1, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 4.2.0-0.bpo.1-amd64 (SMP w/2 CPU cores)
Locale: LANG=fr_CA.UTF-8, LC_CTYPE=fr_CA.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages git-buildpackage depends on:
ii  devscripts            2.15.3
ii  git                   1:2.1.4-2.1+deb8u2
ii  man-db                2.7.0.2-5
ii  python                2.7.9-1
ii  python-dateutil       2.2-2
ii  python-pkg-resources  5.5.1-1

Versions of packages git-buildpackage recommends:
ii  cowbuilder    0.73
ii  pristine-tar  1.33

Versions of packages git-buildpackage suggests:
ii  python-notify  0.1.1-4
ii  unzip          6.0-16+deb8u2

-- no debconf information