bug#57501: call-with-file-lock does not remove lock file

[Ludovic Courtès]

Ricardo Wurmus <rekado@elephly.net> skribis:

> “call-with-file-lock” and “call-with-file-lock/no-wait” create a lock
> file but don’t remove the lock file when they exit.
>
> (guix build syscalls) defines these procedures with “dynamic-wind” so
> that the lock is always lifted with “unlock-file”.  While “unlock-file”
> uses the fcntl syscall to remove the lock on the file, the lock file
> itself is not deleted.
>
> I think it should be deleted.  When the lock file sticks around we may
> run into problems due to lock file ownership.  For example, imagine a
> cron job running as a different user that upgrades the contents of a
> user profile.  That cron job would leave behind an unlocked lock file
> owned by that user, preventing the owner of the profile from operating
> on the profile even though the lock has already been lifted with
> “unlock-file”.
>
> I propose letting either unlock-file or with-profile-lock delete the
> lock file.

Agreed.  Done in a68229b9a0f450db622511adfe00ff7307d745d3, thanks!

Ludo’.