From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Subject: bug#35387: unpack phase in the gnu-build-system is sometimes
	non-deterministic
Date: Tue, 23 Apr 2019 16:36:40 +0200
Message-ID: <87ef5shjpj.fsf@gnu.org>
References: <87mukh6vjq.fsf@cbaines.net>
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In-Reply-To: <87mukh6vjq.fsf@cbaines.net> (Christopher Baines's message of
	"Tue, 23 Apr 2019 08:16:25 +0100")
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To: Christopher Baines <mail@cbaines.net>
Cc: 35387@debbugs.gnu.org

Hi Chris,

Christopher Baines <mail@cbaines.net> skribis:

> I believe that the direnv package has encountered an issue with the
> gnu-build-system [1].
>
> 1: https://issues.guix.info/issue/35386
>
> Due to the combination of the 'setup-go-environment phase from the
> go-build-system, and the 'unpack phase of the gnu-build-system, there
> are two directories to be considered by first-subdirectory when called
> from the unpack phase.
>
> It seems from direnv that this either consistently, with the package
> working on one machine, or failing consistently on another.
>
> To avoid issues like this in the future, I think it would be good to
> have first-subdirectory raise an error if it's behaviour could be
> non-deterministic.

=E2=80=98file-system-fold=E2=80=99 is just a wrapper around =E2=80=98readdi=
r=E2=80=99 so the order in
which it sees directory entries is non-deterministic.

What about writing it like this:

  (define (first-subdirectory directory)
    "Return the file name of the first sub-directory of DIRECTORY."
    (match (scandir directory
                    (lambda (file)
                      (and (not (member file '("." "..")))
                           (file-is-directory? (string-append directory "/"
                                                              file)))))
      ((first . _) first)))

The result will be deterministic since =E2=80=98scandir=E2=80=99 sorts entr=
ies.

Thanks,
Ludo=E2=80=99.