Add a Gnus command to emojize symbols

* doc/misc/gnus.texi (Article Display): Document it.

* lisp/gnus/gnus-art.el (gnus-treat-emojize-symbols): New user option.
(gnus-treatment-function-alist): Map.
(article-emojize-symbols): New command and keystroke.

doc/misc/gnus.texi

@@ -9843,6 +9843,13 @@ Gravatarify the @code{From} header (@code{gnus-treat-from-gravatar}).
 Gravatarify all mail headers (i.e., @code{Cc}, @code{To})
 (@code{gnus-treat-from-gravatar}).
 
+@item W D e
+@kindex W D e @r{(Summary)}
+@findex gnus-article-emojize-symbols
+Some symbols have both a non-emoji presentation and an emoji
+presentation.  This command will make Gnus choose the emoji presentation
+(@code{gnus-article-emojize-symbols}).
+
 @item W D D
 @kindex W D D @r{(Summary)}
 @findex gnus-article-remove-images
@@ -12185,6 +12192,7 @@ controlling variable is a predicate list, as described above.
 @vindex gnus-treat-capitalize-sentences
 @vindex gnus-treat-overstrike
 @vindex gnus-treat-strip-cr
+@vindex gnus-treat-emojize-symbols
 @vindex gnus-treat-strip-headers-in-body
 @vindex gnus-treat-strip-leading-blank-lines
 @vindex gnus-treat-strip-multiple-blank-lines
@@ -12237,6 +12245,7 @@ possible but those listed are probably sufficient for most people.
 @item gnus-treat-capitalize-sentences (t, integer)
 @item gnus-treat-overstrike (t, integer)
 @item gnus-treat-strip-cr (t, integer)
+@item gnus-treat-emojize-symbols (t, integer)
 @item gnus-treat-strip-headers-in-body (t, integer)
 @item gnus-treat-strip-leading-blank-lines (t, first, integer)
 @item gnus-treat-strip-multiple-blank-lines (t, integer)

etc/NEWS

@@ -157,6 +157,18 @@ change the terminal used on a remote host.
 *** New user option 'mml-attach-file-at-the-end'.
 If non-nil, 'C-c C-a' will put attached files at the end of the message.
 
+** Gnus
+
++++
+*** New user option 'gnus-treat-emojize-symbols'.
+If non-nil, symbols that have an emoji representation will be
+displayed as emojis.
+
++++
+*** New command 'gnus-article-emojize-symbols'.
+This is bound to 'W D e' and will display symbols that have emoji
+representation as emojis.
+
 ** EIEIO
 
 +++

lisp/gnus/gnus-art.el

@@ -1167,6 +1167,19 @@ predicate.  See Info node `(gnus)Customizing Articles'."
   :link '(custom-manual "(gnus)Customizing Articles")
   :type gnus-article-treat-custom)
 
+(defcustom gnus-treat-emojize-symbols nil
+  "Display emoji versions of symbol.
+Some symbols have both a non-emoji presentation and an emoji
+presentation.  This treatment will make Gnus display the latter
+as emojis even when they weren't sent as such.
+
+Valid values are nil, t, `head', `first', `last', an integer or a
+predicate.  See Info node `(gnus)Customizing Articles'."
+  :version "29.1"
+  :group 'gnus-article-treat
+  :link '(custom-manual "(gnus)Customizing Articles")
+  :type gnus-article-treat-custom)
+
 (defcustom gnus-treat-unsplit-urls nil
   "Remove newlines from within URLs.
 Valid values are nil, t, `head', `first', `last', an integer or a
@@ -1650,6 +1663,7 @@ regexp."
 (defvar gnus-article-mime-handle-alist-1 nil)
 (defvar gnus-treatment-function-alist
   '((gnus-treat-strip-cr gnus-article-remove-cr)
+    (gnus-treat-emojize-symbols gnus-article-emojize-symbols)
     (gnus-treat-x-pgp-sig gnus-article-verify-x-pgp-sig)
     (gnus-treat-strip-banner gnus-article-strip-banner)
     (gnus-treat-strip-headers-in-body gnus-article-strip-headers-in-body)
@@ -2360,6 +2374,20 @@ fill width."
       (while (search-forward "\r" nil t)
 	(replace-match "\n" t t)))))
 
+(defun article-emojize-symbols ()
+  "Display symbols (that have an emoji version) as emojis."
+  (interactive nil gnus-article-mode)
+  (when-let ((font (and (display-multi-font-p)
+                        (car (internal-char-font nil ?😀)))))
+    (save-excursion
+      (let ((inhibit-read-only t))
+        (goto-char (point-min))
+        (while (re-search-forward "[[:multibyte:]]" nil t)
+          ;; If there's already a grapheme cluster here, skip it.
+          (when (and (not (find-composition (point)))
+                     (font-has-char-p font (char-after (match-beginning 0))))
+            (insert "\N{VARIATION SELECTOR-16}")))))))
+
 (defun article-remove-trailing-blank-lines ()
   "Remove all trailing blank lines from the article."
   (interactive nil gnus-article-mode)
@@ -4341,6 +4369,7 @@ If variable `gnus-use-long-file-name' is non-nil, it is
            article-fill-long-lines
            article-capitalize-sentences
            article-remove-cr
+           article-emojize-symbols
            article-remove-leading-whitespace
            article-display-x-face
            article-display-face
@@ -4448,6 +4477,7 @@ If variable `gnus-use-long-file-name' is non-nil, it is
        ["Treat overstrike" gnus-article-treat-overstrike t]
        ["Treat ANSI sequences" gnus-article-treat-ansi-sequences t]
        ["Remove carriage return" gnus-article-remove-cr t]
+       ["Emojize Symbols" gnus-article-emojize-symbols t]
        ["Remove leading whitespace" gnus-article-remove-leading-whitespace t]
        ["Remove quoted-unreadable" gnus-article-de-quoted-unreadable t]
        ["Remove base64" gnus-article-de-base64-unreadable t]

lisp/gnus/gnus-sum.el

@@ -2267,6 +2267,7 @@ increase the score of each group you read."
               "x" #'gnus-article-display-x-face
               "d" #'gnus-article-display-face
               "s" #'gnus-treat-smiley
+              "e" #'gnus-article-emojize-symbols
               "D" #'gnus-article-remove-images
               "W" #'gnus-article-show-images
               "F" #'gnus-article-toggle-fonts

lisp/gnus/gnus.el

@@ -2660,6 +2660,7 @@ are always t.")
       gnus-article-hide-headers gnus-article-hide-boring-headers
       gnus-article-treat-overstrike
       gnus-article-remove-cr gnus-article-remove-trailing-blank-lines
+      gnus-article-emojize-symbols
       gnus-article-display-x-face gnus-article-de-quoted-unreadable
       gnus-article-de-base64-unreadable
       gnus-article-decode-HZ