[tex-k] Reproducible builds using pdftex

[Norman Gray]

Greetings.

A variety of hats have been donned in this conversation.  May I put on a 
pedantic hat?

On 3 May 2016, at 22:46, Karl Berry wrote:

> But that is not the author's wish, in theory.  If they use \today, by
> definition they meant *today*, the day the document is being 
> processed.

Not really, or at least not by definition, or at least not by Knuth's 
definition.  The TeXBook says that \today is 'the current date' (p406) 
and that \year is 'current year of our Lord' (p273); p349 mentions that 
'\time, \day, \month, and \year are established at the beginning of a 
job' (and says nothing more about what they are established as).

Certainly, the straightforward meaning of 'currently' is 'the date-time 
in a correctly-adjusted Gregorian calendar when the job is started'.  
But 'current' can mean a larger variety of things in a computing 
context, such as 'current standard input' or 'current working 
directory'.  'Current' in that sense refers to a value of standard 
input, working directory, or indeed time, which is set by the 
environment.

Thus I don't think that SOURCE_DATE_EPOCH_TEX_PRIMITIVES is strictly 
required by any text in the TeXBook.

If I looked at one-line documentation for SOURCE_DATE_EPOCH I for one 
would expect it to change \day, \month and \year as well.  I would find 
it confusingly, annoyingly and perversely inconsistent that it changed 
some date information (in the PDF) but not others (\today).

If it is felt to be useful to distinguish the PDF information from the 
\today information (and at a bit of a stretch I can see why you might 
want to do that), then that would be reasonable functionality.  But 
perhaps the ..._TEX_PRIMITIVES environment variable should default to 
'yes'.  That is 'change some date information but not others' should be 
regarded as the non-default behaviour.

Best wishes,

Norman


-- 
Norman Gray  :  https://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK