image-mode: Advertize viewing as text less eagerly

* lisp/image-mode.el (image-text-based-formats): New defcustom.
(image-mode--setup-mode): Don't show message to show image as text
unless it is a text based image format.  Don't mention key binding
for editing as hex.  (Bug#51961)
(image-mode-as-text): Don't mention key binding for editing as hex.
(image-mode-as-hex): Minor cleanup.

1 files changed, 26 insertions, 17 deletions

diff --git a/lisp/image-mode.el b/lisp/image-mode.el
index 4ee02c0675a..c2b145d1a2e 100644
--- a/lisp/image-mode.el
+++ b/lisp/image-mode.el
@@ -457,6 +457,15 @@ call."
 
 ;;; Image Mode setup
 
+(defcustom image-text-based-formats '(svg xpm)
+  "List of image formats that use a plain text format.
+For such formats, display a message that explains how to edit the
+image as text, when opening such images in `image-mode'."
+  :type '(choice (const :tag "Disable completely" nil)
+                 (repeat :tag "List of formats" sexp))
+  :version "29.1"
+  :group 'image)
+
 (defvar-local image-type nil
   "The image type for the current Image mode buffer.")
 
@@ -695,12 +704,10 @@ Key bindings:
 
   (run-mode-hooks 'image-mode-hook)
   (let ((image (image-get-display-property))
-	(msg1 (substitute-command-keys
-               "Type \\[image-toggle-display] or \\[image-toggle-hex-display] to view the image as "))
-	animated)
+        msg animated)
     (cond
      ((null image)
-      (message "%s" (concat msg1 "an image.")))
+      (setq msg "an image"))
      ((setq animated (image-multi-frame-p image))
       (setq image-multi-frame t
 	    mode-line-process
@@ -718,10 +725,13 @@ Key bindings:
 			  keymap
 			  (down-mouse-1 . image-next-frame)
 			  (down-mouse-3 . image-previous-frame)))))))
-      (message "%s"
-	       (concat msg1 "text.  This image has multiple frames.")))
+      (setq msg "text.  This image has multiple frames"))
      (t
-      (message "%s" (concat msg1 "text or hex."))))))
+      (setq msg "text")))
+    (when (memq (plist-get (cdr image) :type) image-text-based-formats)
+      (message (substitute-command-keys
+                "Type \\[image-toggle-display] to view the image as %s")
+               msg))))
 
 ;;;###autoload
 (define-minor-mode image-minor-mode
@@ -768,11 +778,11 @@ on these modes."
   (image-mode-to-text)
   ;; Turn on hexl-mode
   (hexl-mode)
-  (message "%s" (concat
-                 (substitute-command-keys
-                  "Type \\[image-toggle-hex-display] or \\[image-toggle-display] to view the image as ")
-                 (if (image-get-display-property)
-                     "hex" "an image or text") ".")))
+  (message (substitute-command-keys
+            "Type \\[image-toggle-hex-display] or \
+\\[image-toggle-display] to view the image as %s")
+           (if (image-get-display-property)
+               "hex" "an image or text")))
 
 (defun image-mode-as-text ()
   "Set a non-image mode as major mode in combination with image minor mode.
@@ -788,11 +798,10 @@ See commands `image-mode' and `image-minor-mode' for more information
 on these modes."
   (interactive)
   (image-mode-to-text)
-  (message "%s" (concat
-                 (substitute-command-keys
-                  "Type \\[image-toggle-display] or \\[image-toggle-hex-display] to view the image as ")
-                 (if (image-get-display-property)
-                     "text" "an image or hex") ".")))
+  (message (substitute-command-keys
+            "Type \\[image-toggle-display] to view the image as %s")
+           (if (image-get-display-property)
+               "text" "an image")))
 
 (defun image-toggle-display-text ()
   "Show the image file as text.