Re: [PATCH] org-latex-compile timestamp checks

[Rasmus <rasmus@gmx.us>]

Hi Anthony and Nicolas,

Anthony Cowley <acowley@gmail.com> writes:

> Thanks for taking a look, Rasmus! The bug is in Org, not Emacs. One
> may perhaps assume the invariant that successive calls to
> `current-time` will return non-decreasing values. One might also
> assume the invariant that successive touches of different files will
> result in file attributes with non-decreasing timestamps. It is mixing
> the two that is the bug, and Emacs itself shouldn’t try to fix
> that. To be clear, the limiting factor in this comparison is the
> filesystem whose timestamp granularity is much coarser than the system
> clock.

Thanks for carefully explaining exactly what is going on here.

> We could do something like generate an entirely separate temporary
> file before compilation, and use its timestamp as the reference by
> which compilation output is evaluated. However, the approach of
> checking file freshness with a one-second granularity seems like a
> pretty good compromise.

I think the approach is fine now.  See below.

>> Maybe you could just check the log directly for failures rather than
>> checking the file attributes, if these are not reliable.
>> 
>> Also, what is the ‘take‘?  I don’t seem to have it in my Emacs…
>
> Sorry about that. Believe it or not I had already rewritten those two
> lines — as simple as they are — trying to not include extra
> dependencies. I’ve attached an updated patch that uses subseq from
> cl.el. I hope that is okay.

Actually, it's part of cl-lib now (in the broadest understanding of
cl-lib).

Since this is a bugfix I guess you should use org-sublist (*shiver*) in
maint and cl-subseq in master.  We can’t use cl-lib in maint, right
Nicolas?

Nicolas Goaziou <mail@nicolasgoaziou.fr> writes:

> Anthony Cowley <acowley@gmail.com> writes:
>
>> * lisp/ox-latex.el (org-latex-compile): Improve timestamp check on HFS+
>>   filesystem by only considering 1-second clock resolution.
>>
>> Previously, the call to (current-time) could return a timestamp with
>> a non-zero microsecond or picosecond fields, while the file attribute
>> always has zeros for these fields. The check that the generated file is
>> newer than the reference timestamp only succeeded when the time to
>> generate the file crossed a 1-second clock interval.
>>
>> TINYCHANGE
>> ---
>>  lisp/ox-latex.el | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/lisp/ox-latex.el b/lisp/ox-latex.el
>> index a57677b..f803b7e 100644
>> --- a/lisp/ox-latex.el
>> +++ b/lisp/ox-latex.el
>> @@ -3576,7 +3576,8 @@ Return PDF file name or an error if it couldn't be produced."
>>  	;; Check for process failure.  Provide collected errors if
>>  	;; possible.
>>  	(if (or (not (file-exists-p pdffile))
>> -		(time-less-p (nth 5 (file-attributes pdffile)) time))
>> +		(time-less-p (subseq (nth 5 (file-attributes pdffile)) 0 2)
>> +			     (subseq time 0 2)))
>
> This sounds good. Thank you.
>
> Although, I suggest to use `cl-subseq' instead of its alias. Also, it
> may be worth commenting that trick right into the source.

Yes, it should.

> Eventually, I think at least ox-texinfo.el, ox-man.el and ox-groff.el
> need a similar trick.

Perhaps there should be an error check in ox-odt as well?  I guess the
only thing that could happen is that the zip/odt can’t be written, which
could happen if it’s open in windows, which is extremely picky with locked
files.  [I have had to use a windows machine at work].

> Rasmus, what do you think?

I looked at the source, and in the case of ox-latex.el it looks like we
cannot log at the log as org-latex-pdf-process can be a function.  As such
I guess file time stamp is indeed a fine proxy.

Thanks,
Rasmus

-- 
Spil noget med Slayer!