Stefan Kangas <stefankangas@gmail.com> writes:

> Philip Kaludercic <philipk@posteo.net> writes:
>
>> From 761ee105380c60bcf410e3f3f6e15af8073b1549 Mon Sep 17 00:00:00 2001
>> From: Philip Kaludercic <philipk@posteo.net>
>> Date: Thu, 7 Mar 2024 10:06:48 +0100
>> Subject: [PATCH] Ensure default-directory exists when generating diff
>>
>> * lisp/vc/diff.el (diff-no-select): Fall back to a fresh temporary
>> directory if 'default-directory' points to an invalid path.
>> ---
>>  lisp/vc/diff.el | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
>> index 70497a97d56..1aa4f87d1ea 100644
>> --- a/lisp/vc/diff.el
>> +++ b/lisp/vc/diff.el
>> @@ -188,7 +188,9 @@ diff-no-select
>>                                    (list (or old-alt old)
>>                                          (or new-alt new)))))
>>  		     " "))
>> -	 (thisdir default-directory))
>> +	 (thisdir (if (file-exists-p default-directory)
>> +                      default-directory
>> +                    (make-temp-file "emacs-diff" t))))
>>      (with-current-buffer buf
>>        (setq buffer-read-only t)
>>        (buffer-disable-undo (current-buffer))
>> --
>> 2.47.2
>
> Can we please also remove the temporary directory when we're done?

Sure, this should do the job: