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

[Juri Linkov <juri@linkov.net>]

>> > 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,

Installed.

> but wasn't the problem also with creation of a backup file?

Creation of a backup file is not a problem, because backups are created
on saving.  Visiting a file from a zip archive doesn't save it, and
thus doesn't create a backup.  But when the user explicitly saves
a file inside a zip archive, only then it should modify the time
of its directory.