[Reproducible-builds] LaTeX's \today

[Alexis Bienvenüe]

Hi.

Looking at debian package canl-c, I saw it uses \today in the
documentation LaTeX files, so that it can't build reproducibly.
I also heard about gle-graphics [1], which has to be patched to give a
fixed value to \today.

Can we consider turning LaTeX into using SOURCE_DATE_EPOCH (when
available) as \today's epoch? Maybe a way to do this is telling
get_date_and_time to honour SOURCE_DATE_EPOCH. As this function is used
to give a value to the \day, \month and \year LaTeX primitives, this
should be ok. See attached patch for an example.

However, some little more work has to be done if we need the same result
for lualatex and xelatex, as shown in the attached test.

Regards,
Alexis Bienvenüe.

[1]
https://lists.alioth.debian.org/pipermail/reproducible-builds/Week-of-Mon-20160328/005135.html
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