Eli Zaretskii <eliz@gnu.org> writes:

>> From: Dan Jacobson <jidanni@jidanni.org>
>> Cc: 60896@debbugs.gnu.org,control@debbugs.gnu.org
>> Date: Wed, 25 Jan 2023 10:51:43 +0800
>>
>> Well, if the file is not in 7z format,
>> then I hope dired-view-file would make an error message,
>> like it does if a file is not in .gz format:
>> ---
>> Error while executing "gzip -c -q -d < /tmp/x.gz"
>>
>>
>> gzip: stdin: not in gzip format
>
> That gzip error message comes from the gzip program, not from Emacs.
> What does 7z say in a similar case?  That's what dired-view-file
> should show.

See the attachments for example outputs.  #1 is a malformed 7z archive
(in my case just an empty file created by `touch`), and #2 contains an
actual 7z archive created by `7z a 2.7z memsize.c`.

Best,


RY