bug#61394: 30.0.50; [PATCH] Image-dired thumb name based on content

[Manuel Giraud via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Manuel Giraud <manuel@ledu-giraud.fr>
>> Cc: stefankangas@gmail.com,  contovob@tcd.ie,  61394@debbugs.gnu.org
>> Date: Wed, 02 Aug 2023 20:00:19 +0200
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > Thanks.  Maybe I'm missing something, but isn't the problem limited to
>> > just one method of naming the thumbnail files?  If so, shouldn't these
>> > changes be limited to that method alone?
>> 
>> Yes.  First I had a test about the method around the call to
>> 'image-dired-update-thumbnail-at-point' but then I realize that nothing
>> will be done for others methods as I'm doing a test on the thumb name
>> change:
>>         ... (unless (string= thumb old-thumb) ...
>
> This at least warrants a comment, so that others won't have to be
> bothered by the same questions.

What about this one?  I've also permuted some instructions to avoid a
flicker when updating the thumbnail.
-- 
Manuel Giraud

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From 4759066712e9cec4906f95a96b3c6b023149eade Mon Sep 17 00:00:00 2001
From: Manuel Giraud <manuel@ledu-giraud.fr>
Date: Tue, 1 Aug 2023 18:56:33 +0200
Subject: [PATCH] Fix thumbnail update when thumb name is based on image
 content

* lisp/image/image-dired-util.el
(image-dired-update-thumbnail-at-point): New function to update
thumbnail when original image contents changed.

* lisp/image/image-dired-external.el
(image-dired-rotate-original): Use it.

* lisp/image/image-dired.el (image-dired-display-thumbs): Fix
spacing while here.
---
 lisp/image/image-dired-external.el |  3 ++-
 lisp/image/image-dired-util.el     | 18 ++++++++++++++++++
 lisp/image/image-dired.el          |  2 +-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/lisp/image/image-dired-external.el b/lisp/image/image-dired-external.el
index 9f35e17a7e6..77352c25a3b 100644
--- a/lisp/image/image-dired-external.el
+++ b/lisp/image/image-dired-external.el
@@ -405,7 +405,8 @@ image-dired-rotate-original
                 (not image-dired-rotate-original-ask-before-overwrite))
             (progn
               (copy-file image-dired-temp-rotate-image-file file t)
-              (image-dired-refresh-thumb))
+              (image-dired-refresh-thumb)
+              (image-dired-update-thumbnail-at-point))
           (image-dired-display-image file))))))
 
 \f
diff --git a/lisp/image/image-dired-util.el b/lisp/image/image-dired-util.el
index 70911bce45a..40e90e6dcb8 100644
--- a/lisp/image/image-dired-util.el
+++ b/lisp/image/image-dired-util.el
@@ -190,6 +190,24 @@ image-dired-image-at-point-p
   "Return non-nil if there is an `image-dired' thumbnail at point."
   (get-text-property (point) 'image-dired-thumbnail))
 
+(defun image-dired-update-thumbnail-at-point ()
+  "Update the thumbnail at point if the original image file has been
+modified.  Take care of uncaching and removing the old thumbnail
+file."
+  (when (image-dired-image-at-point-p)
+    (let* ((file (image-dired-original-file-name))
+           (thumb (expand-file-name (image-dired-thumb-name file)))
+           (image (get-text-property (point) 'display)))
+      (when image
+        (let ((old-thumb (plist-get (cdr image) :file)))
+          ;; If 'thumb' and 'old-thumb' are the same file names, do
+          ;; nothing.  This would be the case when
+          ;; 'image-dired-thumb-naming' is set to 'sha1-filename'.
+          (unless (string= thumb old-thumb)
+            (setf (plist-get (cdr image) :file) thumb)
+            (clear-image-cache old-thumb)
+            (delete-file old-thumb)))))))
+
 (defun image-dired-window-width-pixels (window)
   "Calculate WINDOW width in pixels."
   (declare (obsolete window-body-width "29.1"))
diff --git a/lisp/image/image-dired.el b/lisp/image/image-dired.el
index 98596510ec1..33beb5b3e49 100644
--- a/lisp/image/image-dired.el
+++ b/lisp/image/image-dired.el
@@ -590,7 +590,7 @@ image-dired-display-thumbs
 `image-dired-previous-line-and-display' where we do not want the
 thumbnail buffer to be selected."
   (interactive "P" nil dired-mode)
-  (setq image-dired--generate-thumbs-start  (current-time))
+  (setq image-dired--generate-thumbs-start (current-time))
   (let ((buf (image-dired-create-thumbnail-buffer))
         files dired-buf)
     (if arg
-- 
2.40.0