Subject: Re: [bug#49517] [PATCH] gnu: txr: Build documentation and update to 265.

From: Kaz Kylheku <[email-masked]>
Date: Sat, 17 Jul 2021 20:43:36 -0700

On 2021-07-17 15:51, Kaz Kylheku wrote:
> On 2021-07-17 02:57, Guillaume Le Vaillant wrote:
>> Hi,
>> 
>> When testing the patch to build the HTML and PDF documentation,
>> I noticed that the 'share/doc/txr-263/txr-manpage.pdf' file is not
>> reproducible. There are some timestamps and UUIDs in it that change at
>> each build (diffoscope output attached).
>> 
>> Could you take a look at that and see if there's a way to make it
>> reproducible?
>> Thanks.
> 
> Hi Guillaume,
> 
> Thank you for your report. I don't see anything in the pdfroff 
> documentation
> about getting rid of this. I might use a program similar to this one
> to just overwrite the UUIDs and dates:

I've noticed that there are some dates in the document which
respond to SOURCE_DATE_EPOCH:

   2 0 obj
   <</Producer(GPL Ghostscript 9.26)
   /CreationDate(D:20210717203740-07'00')
   /ModDate(D:20210717203740-07'00')
   /Creator(groff version 1.22.3)>>endobj

If I build with the SOURCE_DATE_EPOCH environment variable,
these dates from Ghostscript follow that variable.
That's why Guillaume isn't seeing an issue in that section
of the file.

Here is what I am going with:

commit 8fbf3f55446427c06248ce222a05fd09d77ac878 (HEAD -> master)
Author: Kaz Kylheku <[email-masked]>
Date:   Sat Jul 17 19:11:20 2021 -0700

     doc: reproducible PDF.

     * Makefile (txr-manpage.pdf): If SOURCE_DATE_EPOCH exists,
     then run pdf-clobber-stamps.tl.

     * pdf-clobber-stamps.tl: New file.

diff --git a/Makefile b/Makefile
index 0094985f..cac9b3c0 100644
--- a/Makefile
+++ b/Makefile
@@ -560,6 +560,7 @@ txr-manpage.html: txr.1 genman.txr
  txr-manpage.pdf: txr.1 checkman.txr
         $(TXR) checkman.txr $<
         tbl $< | pdfroff -ww -man --no-toc - > $@
+       [ $$SOURCE_DATE_EPOCH ] && $(TXR) pdf-clobber-stamps.tl || true

  #
  # Special targets used by ./configure
diff --git a/pdf-clobber-stamps.tl b/pdf-clobber-stamps.tl
new file mode 100644
index 00000000..0e56a44d
--- /dev/null
+++ b/pdf-clobber-stamps.tl
@@ -0,0 +1,19 @@
+(let* ((epoch (or (tointz (getenv "SOURCE_DATE_EPOCH")) 0))
+       (isotime (time-string-utc epoch "%FT%T+00:00"))
+       (pdf (file-get-string "txr-manpage.pdf"))
+       (start (search-str pdf "<?xpacket begin="))
+       (end (if start (search-str pdf "<?xpacket end" start)))
+       (xml (if end [pdf start..end]))
+       (orig-len (len xml)))
+  (unless xml
+    (format *stderr* "XML block not found in PDF")
+    (exit nil))
+  (upd xml
+    (regsub #/uuid:........-....-....-....-............/
+            "uuid:00000000-0000-0000-0000-000000000000")
+    (regsub #/Date>....-..-..T..:..:..-..:../
+            `Date>@isotime`))
+  (assert (eql (len xml) orig-len))
+  (set [pdf start..end] xml)
+  (file-put-string "txr-manpage.pdf.temp" pdf)
+  (rename-path "txr-manpage.pdf.temp" "txr-manpage.pdf"))