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

[Juri Linkov <juri@linkov.net>]

>> Visiting a file from zip archive changes the modification time of
>> its directory.  It's possible to prevent directory time modification
>> by setting ‘buffer-file-truename’ later after the extractor prepares
>> the file in its buffer:
>
> Sorry, I don't think I understand what you are saying (and if I did, I
> cannot reproduce it).  I visited a random zip archive on my system,
> then pressed RET on one of the files, then killed the buffer which
> visited that file -- and didn't see any changes in the time stamps
> recorded in the zip archive.  Which is what I'd expect, since visiting
> a file from an archive doesn't rewrite the archive, nor modifies it in
> any other way.
>
> What am I missing?

It modifies the time of the directory where the zip archive is located,
e.g. visiting a file inside ~/dir/file.zip modifies the time of the
directory ~/dir/ because during unzipping in that directory, arc-mode
creates a temporary backup with the file name from ‘buffer-file-truename’.
Setting ‘buffer-file-truename’ later prevents from creating this
unnecessary backup copy that modifies the directory time.