[Reproducible-builds] Bug#801621: perl: support SOURCE_DATE_EPOCH in Pod::Man

[Niko Tyni]

Package: perl
Version: 5.22.0-4
Severity: wishlist
Tags: upstream patch
User: reproducible-builds at lists.alioth.debian.org
Usertags: timestamps
X-Debbugs-Cc: Russ Allbery <rra at debian.org>, reproducible-builds at lists.alioth.debian.org

(cc'ing Russ as the podlators upstream author)

Since 5.20.1~rc1-1, Pod::Man has supported the POD_MAN_DATE environment
variable for overriding the page footers, fixing #759405. Since then,
the reproducible builds project has converged on the SOURCE_DATE_EPOCH
specification, which "defines a distribution-agnostic standard for
upstream build processes to consume this timestamp from packaging
systems."

It would be good to have Pod::Man support the SOURCE_DATE_EPOCH
environment variable, either instead of or in addition to POD_MAN_DATE,
which is specific to the podlators modules. This would give distributions
aiming for reproducible builds automatic benefits from standardizing on
SOURCE_DATE_EPOCH, without having to add a special case for Pod::Man.

In the context of Debian, while it's possible to set POD_MAN_DATE
externally based on SOURCE_DATE_EPOCH, it's not clear which layer
should do this. Options include dpkg-buildpackage, where special casing
POD_MAN_DATE looks particularly wrong, and debhelper, where this should
probably go in the v9 based dh_auto_* build systems, perhaps only the
Perl ones (perl_build and perl_makemaker). In particular, packages using
old style debhelper debian/rules do not have a place where POD_MAN_DATE
could be injected centrally in debhelper, which would leave out many
packages that would otherwise profit from this.

The attached patch against the current podlators upstream git
repository implements support for SOURCE_DATE_EPOCH in addition to
POD_MAN_DATE. Russ, please let me know what you think. I see POD_MAN_DATE
support hasn't been released upstream yet, so I suppose even backing
that out altogether would still be a valid option if you want to avoid
duplicating the functionality.
-- 
Niko Tyni   ntyni at debian.org
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