bug#23776: Perl's .pod files include timestamps, making Perl package builds non-deterministic

[ludo@gnu.org (Ludovic Courtès)]

Leo Famulari <leo@famulari.name> skribis:

> On Thu, Jun 16, 2016 at 11:39:27AM -0400, Leo Famulari wrote:
>> On Thu, Jun 16, 2016 at 01:33:46PM +0200, Ludovic Courtès wrote:
>> > The problem is described in <git://git.debian.org/git/reproducible/notes.git>:
>> > 
>> > --8<---------------cut here---------------start------------->8---
>> > timestamps_in_documentation_generated_by_podman:
>> >   description: |
>> >     The module Pod::Man includes timestamps in its embedded manpages:
>> >     http://sources.debian.net/src/perl/latest/cpan/podlators/lib/Pod/Man.pm/?hl=1700#L977
>> >     They should be based on the mtime of the original file.
>> >   url: https://wiki.debian.org/ReproducibleBuilds/TimestampsInManpagesGeneratedByPodMan
>> 
>> According to the information on this page, we should set POD_MAN_DATE
>> while building. Should we make the perl-build-system export this
>> variable? Set to SOURCE_DATE_EPOCH?
>
> I noticed that Pod::Man is supposed to respect SOURCE_DATE_EPOCH, as of
> the upstream module version 4.03 (released 2015-12-06). Does anyone know
> how to check the version of the module bundled into perl?

For the record, even though Pod::Man supposedly honors SOURCE_DATE_EPOCH
as of Perl 5.24, we still have this problem:

--8<---------------cut here---------------start------------->8---
$ diff -r /gnu/store/hczskszmhm2l65vy8nv990lzc5dk3ln9-perl-algorithm-c3-0.10{,-check}
diff -r /gnu/store/hczskszmhm2l65vy8nv990lzc5dk3ln9-perl-algorithm-c3-0.10/lib/perl5/5.24.0/x86_64-linux-thread-multi/perllocal.pod /gnu/store/hczskszmhm2l65vy8nv990lzc5dk3ln9-perl-algorithm-c3-0.10-check/lib/perl5/5.24.0/x86_64-linux-thread-multi/perllocal.pod
1c1
< =head2 Wed Jan 11 22:20:36 2017: C<Module> L<Algorithm::C3|Algorithm::C3>
---
> =head2 Wed Jan 11 22:20:34 2017: C<Module> L<Algorithm::C3|Algorithm::C3>
--8<---------------cut here---------------end--------------->8---

Ludo’.