Subject: Automake output non-deterministic when used with later Perls
From: demerphq <[email-masked]>
To: [email-masked]
Date: Mon, 6 Feb 2017 03:32:11 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

Some time back I switched Perl to using a randomly seeded hash
function. (I am a core perl committer, and I do a lot of work on its
hash function.)

A consequence of this is that default output from tools like
Data::Dumper is non-deterministic, meaning output files under source
control, etc, change unnecessarily every time.

At least part of the automake toolset is affected, for instance autom4te.

For autom4te a simple solution is to add:

$Data::Dumper::Sortkeys = 1;

to the script. This seems to fix the problem I was observing, but an
audit of the use of  the "keys" function to ensure that any such use
for output is sorted will eliminate this class of errors.

I would be happy to put together a pull request, or a patch if you
could point me to the relevant repository. (Which does not appear to
be documented in the installed versions of automake, although I may
have overlooked it.)

I am sorry I cannot give a better reproduction description than this:

while hacking the "dieharder" package I observed that after running
"autoreconf -i" that the file ./autom4te.cache/requests file changed
in ways that it should not have. Opening the file I observed it
contains output clearly from the Perl Data::Dumper module, I then made
the patch to autom4te described above, and observed that after running
"autoreconf -i" again the output was sorted, and that after running it
yet again the file was unchanged.

Classic unsorted use of undefined hash order bug that we had to do a
lot of cleanup in the Perl world around the time of Perl 5.10

Thanks,
Yves

-- 
perl -Mre=debug -e "/just|another|perl|hacker/"