bug#35387: unpack phase in the gnu-build-system is sometimes non-deterministic

["Ludovic Courtès" <ludo@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.

‘file-system-fold’ is just a wrapper around ‘readdir’ 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 ‘scandir’ sorts entries.

Thanks,
Ludo’.