bug#69606: [PATCH] Ensure default-directory exists when generating diff

[Philip Kaludercic <philipk@posteo.net>]

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When I generate a diff in some directory that I would afterwards delete,
the diff buffer appears to remain in the now non-existent directory
(according to `default-directory'), even if I want to generate a diff
for some other file.  The issue now is that make-process complains that
it cannot set the CWD when starting "diff", and instead fails with a
slightly confusing error message:

  start-process: Setting current directory: No such file or directory, /some/directory/that/doesnt/exist/anymore

This would fix the issue, but I don't think the solution is ideal:


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From 73a93310a9f38b15a7a849b75b4ea2b3805041ad 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 the users home
directory if default-directory is not a valid 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 a64fbc47853..47566dbc40b 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
+                    (expand-file-name "~"))))
     (with-current-buffer buf
       (setq buffer-read-only t)
       (buffer-disable-undo (current-buffer))
-- 
2.44.0


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Any other ideas?  Perhaps we should always set the default directory to
that 

-- 
	Philip Kaludercic on peregrine