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

[Christopher Baines <mail@cbaines.net>]

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Ludovic Courtès <ludo@gnu.org> writes:

> 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.

That sounds great :)

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