[Bug 2003201] Re: Please merge sbuild 0.85.0 from Debian unstable.

[Dave Jones]

Confirmed this is due to changes in the output of libzstd1. The current
variant of libzstd1 in lunar (1.5.4) produces entirely different output
in the diffoscope diff of the generated deb. Compare the diffoscope
output in [1] to [2]. I reproduced these differences in an otherwise up
to date lunar VM by downgrading the libzstd1 package from 1.5.4+dfsg2-4
to 1.5.2+dfsg-1.

[1]: https://autopkgtest.ubuntu.com/results/autopkgtest-
lunar/lunar/arm64/s/sbuild/20230204_040321_7a8f5@/log.gz

[2]: https://autopkgtest.ubuntu.com/results/autopkgtest-
lunar/lunar/arm64/s/sbuild/20230320_055722_83889@/log.gz

I theorize, that the last successful version was 1.4.8+dfsg-3build1
(last seen in kinetic and current in jammy). However I can't currently
test with that as dpkg has depended on libzstd1 >= 1.5.2 for a while
now.

Anyway, the crux of the problem is that the unshare test is checking for
binary reproducibility of output, and zstd doesn't guarantee that (does
any compressor guarantee that, or have we just got lucky so far?).
Solutions:

1) Drop the diffoscope part of the unshare test

2) Update the diffoscope part of the unshare test to the "current zstd
output" (and presumably keep doing this with each new zstd version)

3) Find some way of beating zstd into producing the same output as
before (if that's possible)

The first is easiest and quickest but nasty, the second still fairly
quick'n'easy but potentially painful in future (and seems somewhat
against the spirit of the test anyway). The third is potentially
impossible and if possible, potentially hard.

Incidentally, all of the above presumably apply to Debian too now zstd
deb support has made its way upstream.

Comments?

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https://bugs.launchpad.net/bugs/2003201

Title:
  Please merge sbuild 0.85.0 from Debian unstable.

Status in sbuild package in Ubuntu:
  In Progress

Bug description:
  Please merge sbuild 0.85.0 from Debian unstable.

  Updated changelog and diff against Debian unstable to be attached
  below.

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