On Thu, May 5, 2016 at 3:06 PM, Norbert Preining <preining@logic.at> wrote:

On Thu, 05 May 2016, luigi scarso wrote:
> what happen if Windows decide to reserve SOURCE_DATE_EPOCH for their own
> use ?

Well, sure, but that can happen with each and everything.

sure, and the side effects is something that we want to avoid.

> Is SOURCE_DATE_EPOCH standard ?

Well, at least several distributions and projects are working on
similar stuff, see
https://reproducible-builds.org/
and
https://reproducible-builds.org/specs/source-date-epoch/

Of course, windows is not one of them.

Weren't texmf.cnf & kpathsea created also to solve these kind of problems ?

On the other side, if you really want a reproducible doc from source

you have to use Knuth's tex & dvi & mf & your own format and mf fonts and the convert to pdf in a predictable way.

If you want a pdf directly from sources, better to provide *tex sources & pdf and say that the *tex sources are the reference

or the pdf is the reference (which is the best solution, if the pdf is pdf/a-2) but not both.

If you want to reproduce pdf from the source with luatex, you must use a very carefully crafted format

and the builders and "reproducers" must agree at least on the same engine, format & fonts

as also on the meaning of "=" for pdfs -- and then cross the fingers.

Nobody can exclude that a library (say poppler) will use a hash table for (some of) the pdf objs of the backend,

and even if you "control" the libs of Luatex nobody can prevent to use Luatex with a shared lib API compatible,

and even if you make a static Luatex only nobody can prevent to use a format that uses Lua (hash) table for the pdf objs...

all these can lead to two pdf that are "visually" the same but different as binaries.

And comparing the visual appearance of two pdf is not simple, unless you don't fix a dpi --- which means A=B at, say, 300 dpi, but perhaps A!=B at 1200dpi.

Of course you can solve these problem if the builder freezes the set of engine & format & fonts etc used and reproducers use exactly the same set, even after 20years the first official build.

This is a really interesting subject, but the time is only a component, and as I have said, we are discussing of it.

luigi