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.

1 files changed, 6 insertions, 2 deletions

diff --git a/etc/NEWS b/etc/NEWS
index bfcb7cf3255..5e412f2b557 100644
--- a/etc/NEWS
+++ b/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
-according to the orientation in the Exif data, if any.
+*** 'auto-mode-alist' now includes many of the types typically
+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