> In the interim, we can set it in a phase of ‘emacs-build-system’, which
> would entail few rebuilds.
>
> WDYT?

I think it is not so important to make a temporary workaround for
master.  What about just fixing it in core-updates?

>> +++ b/gnu/packages/patches/emacs-source-date-epoch.patch
>> @@ -0,0 +1,20 @@
>> +Honor SOURCE_DATE_EPOCH variable to avoid non-determinism in generated
>> +"autoloads" files.
>> +
>> +--- a/lisp/emacs-lisp/autoload.el
>> ++++ b/lisp/emacs-lisp/autoload.el
>> +@@ -378,8 +378,12 @@
>> +   "Insert the section-header line,
>> + which lists the file name and which functions are in it, etc."
>> +   (insert generate-autoload-section-header)
>> +-  (prin1 `(autoloads ,autoloads ,load-name ,file ,time)
>> +-	 outbuf)
>> ++  (let* ((env  (getenv "SOURCE_DATE_EPOCH"))
>> ++         (time (if env
>> ++                   (seconds-to-time (string-to-number env))
>> ++                 time)))
>> ++    (prin1 `(autoloads ,autoloads ,load-name ,file ,time)
>> ++           outbuf))
>> +   (terpri outbuf)
>> +   ;; Break that line at spaces, to avoid very long lines.
>> +   ;; Make each sub-line into a comment.
>
> Could you also submit it upstream, Cc’ing guix-devel and
> reproducible-builds@lists.alioth.debian.org?  Hopefully that is
> acceptable.  (I searched a bit but didn’t find a similar patch by the
> Debian Reproducible team, but patch-tracker.debian.org is unreachable.)

I'm afraid it's a too hard task for me, sorry.  I wouldn't like to mail
to so many places.

Sorry for the long delay.

-- 
Alex