bug#30215: Visiting files from zip archives should not modify directory time

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: 30215@debbugs.gnu.org
> Date: Wed, 24 Jan 2018 23:36:10 +0200
> 
> > If that's the problem, then I think it would be cleaner to disable
> > creation of lock files and backup files by less subtle means -- by
> > let-binding create-lockfiles and make-backup-files.  Doing that by
> > leaving buffer-file-truename at nil leaves the code less clear IMO,
> > and relies on assumptions that might not hold at some future point.
> 
> Thanks for the suggestion, this is better indeed:
> 
> diff --git a/lisp/arc-mode.el b/lisp/arc-mode.el
> index adb3669..4fe1b03 100644
> --- a/lisp/arc-mode.el
> +++ b/lisp/arc-mode.el
> @@ -807,7 +807,7 @@ archive-summarize
>  Optional argument SHUT-UP, if non-nil, means don't print messages
>  when parsing the archive."
>    (widen)
> -  (let ((buffer-file-truename nil) ; avoid changing dir mtime by lock_file
> +  (let ((create-lockfiles nil) ; avoid changing dir mtime by lock_file

This LGTM, but wasn't the problem also with creation of a backup file?