Default exotic image formats (like .webp) to image-mode

* doc/lispref/errors.texi (Standard Errors): Mention the new error.

* lisp/files.el (auto-mode-alist): Add a bunch of image suffixes
to the list (bug#37972) based on the output from "gm convert -list
format" (i.e., graphicsmagick).

* lisp/image-mode.el (image-mode): Rewrite to possibly notify the
user about image-use-external-converter.
(image-mode--setup-mode): Factor out into own function and don't
run under `condition-case' as there's nothing here that should
error.

* lisp/image.el (unknown-image-type): New error.
(image-type): Signal that error so that image-mode can offer
sensible feedback to the user.

doc/lispref/errors.texi

@@ -215,6 +215,9 @@ The message is @samp{Wrong number of arguments}.  @xref{Argument List}.
 
 @item wrong-type-argument
 The message is @samp{Wrong type argument}.  @xref{Type Predicates}.
+
+@item unknown-image-type
+The message is @samp{Cannot determine image type}.  @xref{Images}.
 @end table
 
 @ignore    The following seem to be unused now.

etc/NEWS

@@ -2933,6 +2933,9 @@ data about creation times and orientation and the like.
 'exif-parse-file' and 'exif-parse-buffer' are the main interface
 functions.
 
+*** 'image-mode' now uses this library to automatically rotate images
+according to the orientation in the Exif data, if any.
+
 *** New library image-converter.
 If you need to view exotic image formats for which Emacs doesn't have
 native support, customize the new user option
@@ -2940,8 +2943,9 @@ native support, customize the new user option
 GraphicsMagick, ImageMagick or 'ffmpeg' installed, they will then be
 used to convert images automatically before displaying them.
 
-*** 'image-mode' now uses this library to automatically rotate images
+*** 'auto-mode-alist' now includes many of the types typically
-according to the orientation in the Exif data, if any.
+supported by the external image converters, like WEPB, BMP and ICO.
+These now default to using 'image-mode'.
 
 *** 'imagemagick-types-inhibit' disables using ImageMagick by default.
 'image-mode' started using ImageMagick by default for all images

lisp/files.el

@@ -2847,7 +2847,51 @@ ARC\\|ZIP\\|LZH\\|LHA\\|ZOO\\|[JEW]AR\\|XPI\\|RAR\\|CBR\\|7Z\\)\\'" . archive-mo
      ;; The following should come after the ChangeLog pattern
      ;; for the sake of ChangeLog.1, etc.
      ;; and after the .scm.[0-9] and CVS' <file>.<rev> patterns too.
-     ("\\.[1-9]\\'" . nroff-mode)))
+     ("\\.[1-9]\\'" . nroff-mode)
+     ;; Image file types probably supported by `image-convert'.
+     ("\\.art\\'" . image-mode)
+     ("\\.avs\\'" . image-mode)
+     ("\\.bmp\\'" . image-mode)
+     ("\\.cmyk\\'" . image-mode)
+     ("\\.cmyka\\'" . image-mode)
+     ("\\.crw\\'" . image-mode)
+     ("\\.dcr\\'" . image-mode)
+     ("\\.dcx\\'" . image-mode)
+     ("\\.dng\\'" . image-mode)
+     ("\\.dpx\\'" . image-mode)
+     ("\\.fax\\'" . image-mode)
+     ("\\.hrz\\'" . image-mode)
+     ("\\.icb\\'" . image-mode)
+     ("\\.icc\\'" . image-mode)
+     ("\\.icm\\'" . image-mode)
+     ("\\.ico\\'" . image-mode)
+     ("\\.icon\\'" . image-mode)
+     ("\\.jbg\\'" . image-mode)
+     ("\\.jbig\\'" . image-mode)
+     ("\\.jng\\'" . image-mode)
+     ("\\.jnx\\'" . image-mode)
+     ("\\.miff\\'" . image-mode)
+     ("\\.mng\\'" . image-mode)
+     ("\\.mvg\\'" . image-mode)
+     ("\\.otb\\'" . image-mode)
+     ("\\.p7\\'" . image-mode)
+     ("\\.pcx\\'" . image-mode)
+     ("\\.pdb\\'" . image-mode)
+     ("\\.pfa\\'" . image-mode)
+     ("\\.pfb\\'" . image-mode)
+     ("\\.picon\\'" . image-mode)
+     ("\\.pict\\'" . image-mode)
+     ("\\.rgb\\'" . image-mode)
+     ("\\.rgba\\'" . image-mode)
+     ("\\.tga\\'" . image-mode)
+     ("\\.wbmp\\'" . image-mode)
+     ("\\.webp\\'" . image-mode)
+     ("\\.wmf\\'" . image-mode)
+     ("\\.wpg\\'" . image-mode)
+     ("\\.xcf\\'" . image-mode)
+     ("\\.xmp\\'" . image-mode)
+     ("\\.xwd\\'" . image-mode)
+     ("\\.yuv\\'" . image-mode)))
   "Alist of filename patterns vs corresponding major mode functions.
 Each element looks like (REGEXP . FUNCTION) or (REGEXP FUNCTION NON-NIL).
 \(NON-NIL stands for anything that is not nil; the value does not matter.)

lisp/image-mode.el

@@ -552,8 +552,6 @@ to toggle between display as an image and display as text or hex.
 Key bindings:
 \\{image-mode-map}"
   (interactive)
-  (condition-case err
-      (progn
   (unless (display-images-p)
     (error "Display does not support images"))
 
@@ -561,16 +559,34 @@ Key bindings:
   (setq major-mode 'image-mode)
 
   (if (not (image-get-display-property))
+      (progn
+        (when (condition-case err
                 (progn
 	          (image-toggle-display-image)
+                  t)
+              (unknown-image-type
+               (image-mode-as-text)
+               (funcall
+                (if (called-interactively-p 'any) 'error 'message)
+                "Unknown image type; consider switching `image-use-external-converter' on")
+               nil)
+              (error
+               (image-mode-as-text)
+               (funcall
+                (if (called-interactively-p 'any) 'error 'message)
+                "Cannot display image: %s" (cdr err))
+               nil))
 	  ;; If attempt to display the image fails.
 	  (if (not (image-get-display-property))
-		  (error "Invalid image")))
+	      (error "Invalid image"))
+          (image-mode--setup-mode)))
     ;; Set next vars when image is already displayed but local
     ;; variables were cleared by kill-all-local-variables
     (setq cursor-type nil truncate-lines t
-		image-type (plist-get (cdr (image-get-display-property)) :type)))
+	  image-type (plist-get (cdr (image-get-display-property)) :type))
+    (image-mode--setup-mode)))
 
+(defun image-mode--setup-mode ()
   (setq mode-name (if image-type (format "Image[%s]" image-type) "Image"))
   (use-local-map image-mode-map)
 
@@ -600,9 +616,7 @@ Key bindings:
 		       (format "[%s/%s]"
 			       (1+ (image-current-frame ',image))
 			       ,(car animated))
-			     'help-echo "Frames
+		       'help-echo "Frames\nmouse-1: Next frame\nmouse-3: Previous frame"
-mouse-1: Next frame
-mouse-3: Previous frame"
 		       'mouse-face 'mode-line-highlight
 		       'local-map
 		       '(keymap
@@ -612,17 +626,9 @@ mouse-3: Previous frame"
 			  (down-mouse-3 . image-previous-frame)))))))
       (message "%s"
 	       (concat msg1 "text.  This image has multiple frames.")))
-;;;			     (substitute-command-keys
-;;;			      "\\[image-toggle-animation] to animate."))))
      (t
       (message "%s" (concat msg1 "text or hex."))))))
 
-    (error
-     (image-mode-as-text)
-     (funcall
-      (if (called-interactively-p 'any) 'error 'message)
-      "Cannot display image: %s" (cdr err)))))
-
 ;;;###autoload
 (define-minor-mode image-minor-mode
   "Toggle Image minor mode in this buffer.

lisp/image.el

@@ -151,6 +151,8 @@ or \"ffmpeg\") is installed."
   :type 'boolean
   :version "27.1")
 
+(define-error 'unknown-image-type "Unknown image type")
+
 ;; Map put into text properties on images.
 (defvar image-map
   (let ((map (make-sparse-keymap)))
@@ -391,7 +393,7 @@ Optional DATA-P non-nil means SOURCE is a string containing image data."
                             (require 'image-converter)
                             (image-convert-p source))))))
     (unless type
-      (error "Cannot determine image type")))
+      (signal 'unknown-image-type "Cannot determine image type")))
   (when (and (not (eq type 'image-convert))
              (not (memq type (and (boundp 'image-types) image-types))))
     (error "Invalid image type `%s'" type))