Bug#805488: pristine-tar: Does not efficiently compress gzip --rsyncable, dpkg's default

[Peter Colberg]

Control: found -1 1.37
Control: affects -1 src:twinkle

On Wed, Nov 18, 2015 at 11:50:06AM -0500, Geoffrey Thomas wrote:
> pristine-tar seems not to know how to efficiently re-compress files
> compressed by gzip --rsyncable on both Jessie and Sid (which have gzip
> 1.6-4). From a Sid chroot:
> 
> $ gunzip pristine-tar_1.33.tar.gz
> $ gzip --rsyncable pristine-tar_1.33.tar
> $ pristine-tar gendelta pristine-tar_1.33.tar.gz tmp
> warning: pristine-gz cannot reproduce build of pristine-tar_1.33.tar.gz; storing 80% size diff in delta
> (Please consider filing a bug report so the delta size can be improved.)

I have the same issue with tarballs of twinkle that were repacked by uscan:

# dget -d http://snapshot.debian.org/archive/debian-debug/20160716T102025Z/pool/main/t/twinkle/twinkle_1.10.0%2Bdfsg-1.dsc

# pristine-tar gendelta twinkle_1.10.0+dfsg.orig.tar.gz{,.delta}                                       
xdelta: warning: no matches found in from file, patch will apply without it
xdelta: warning: no matches found in from file, patch will apply without it
xdelta: warning: no matches found in from file, patch will apply without it
xdelta: warning: no matches found in from file, patch will apply without it
xdelta: warning: no matches found in from file, patch will apply without it
warning: pristine-gz cannot reproduce build of twinkle_1.10.0+dfsg.orig.tar.gz; storing 86% size diff in delta (995746 bytes)
(Please consider filing a bug report so the delta size can be improved.)

# gunzip < twinkle_1.10.0+dfsg.orig.tar.gz | gzip -9 --no-name --rsyncable | diff -s - twinkle_1.10.0+dfsg.orig.tar.gz
Files - and twinkle_1.10.0+dfsg.orig.tar.gz are identical

Regards,
Peter