* lisp/international/mule-cmds.el: Use group-function in read-char-by-name.

(mule--ucs-names-group): Simplify for using by group-function.
(read-char-by-name-group): Remove defcustom
obsoleted by completions-group.
(read-char-by-name): Mention completions-group and
completions-group-sort in docstring.  Use group-function when
completions-group is non-nil.
https://lists.gnu.org/archive/html/emacs-devel/2021-05/msg00791.html

etc/NEWS

@@ -1090,12 +1090,11 @@ so e.g. like 'C-x 8 [' inserts a left single quotation mark,
 'C-x \ [' does the same.
 
 ---
-*** New user options 'read-char-by-name-sort' and 'read-char-by-name-group'.
-'read-char-by-name-sort' defines the sorting order of characters for
-completion of 'C-x 8 RET TAB' and can be customized to sort them
-by codepoints instead of character names by default.  The 't' value of
-'read-char-by-name-group' groups the characters for completion of
-'C-x 8 RET TAB' by Unicode blocks.
+*** New user option 'read-char-by-name-sort'.
+It defines the sorting order of characters for completion of 'C-x 8 RET TAB'
+and can be customized to sort them by codepoints instead of character names.
+Additionally, you can group characters by Unicode blocks after customizing
+'completions-group' and 'completions-group-sort'.
 
 ---
 *** Improved language transliteration in Malayalam input methods.
@@ -2767,6 +2766,10 @@ It accepts a list of completions and should return a list where
 each element is a list with three elements: a completion,
 a prefix string, and a suffix string.
 
++++
+** New completion function 'group-function' for grouping candidates.
+It takes two arguments: a completion candidate and a 'transform' flag.
+
 +++
 ** 'read-char-from-minibuffer' and 'y-or-n-p' support 'help-form'.
 If you bind 'help-form' to a non-nil value while calling these functions,

lisp/international/mule-cmds.el

@@ -3104,35 +3104,11 @@ on encoding."
               (list name (concat (if char (list char) " ") "\t") "")))
           names))
 
-(defun mule--ucs-names-group (names)
-  (let* ((codes-and-names
-          (mapcar (lambda (name) (cons (gethash name ucs-names) name)) names))
-         (grouped
-          (seq-group-by
-           (lambda (code-name)
-             (let ((script (aref char-script-table (car code-name))))
-               (if script (symbol-name script) "ungrouped")))
-           codes-and-names))
-         names-with-header header)
-    (dolist (group (sort grouped (lambda (a b) (string< (car a) (car b)))))
-      (setq header t)
-      (dolist (code-name (cdr group))
-        (push (list
-               (cdr code-name)
-               (concat
-                (if header
-                    (progn
-                      (setq header nil)
-                      (concat "\n" (propertize
-                                    (format "* %s\n" (car group))
-                                    'face 'header-line)))
-                  "")
-                ;; prefix
-                (if (car code-name) (format "%c" (car code-name)) " ") "\t")
-               ;; suffix
-               "")
-              names-with-header)))
-    (nreverse names-with-header)))
+(defun mule--ucs-names-group (name transform)
+  (if transform
+      name
+    (let ((script (aref char-script-table (gethash name ucs-names))))
+      (if script (symbol-name script) "ungrouped"))))
 
 (defun char-from-name (string &optional ignore-case)
   "Return a character as a number from its Unicode name STRING.
@@ -3164,14 +3140,6 @@ Defines the sorting order either by character names or their codepoints."
   :group 'mule
   :version "28.1")
 
-(defcustom read-char-by-name-group nil
-  "How to group characters for `read-char-by-name' completion.
-When t, split characters to sections of Unicode blocks
-sorted alphabetically."
-  :type 'boolean
-  :group 'mule
-  :version "28.1")
-
 (defun read-char-by-name (prompt)
   "Read a character by its Unicode name or hex number string.
 Display PROMPT and read a string that represents a character by its
@@ -3185,8 +3153,9 @@ preceded by an asterisk `*' and use completion, it will show all
 the characters whose names include that substring, not necessarily
 at the beginning of the name.
 
-The options `read-char-by-name-sort' and `read-char-by-name-group'
-define the sorting order of completion characters and how to group them.
+The options `read-char-by-name-sort', `completions-group', and
+`completions-group-sort' define the sorting order of completion characters,
+whether to group them, and how to sort groups.
 
 Accept a name like \"CIRCULATION FUNCTION\", a hexadecimal
 number like \"2A10\", or a number in hash notation (e.g.,
@@ -3204,11 +3173,12 @@ as names, not numbers."
 		 `(metadata
 		   (display-sort-function
 		    . ,(when (eq read-char-by-name-sort 'code)
-                         #'mule--ucs-names-sort-by-code))
+			 #'mule--ucs-names-sort-by-code))
 		   (affixation-function
-		    . ,(if read-char-by-name-group
-                           #'mule--ucs-names-group
-                         #'mule--ucs-names-affixation))
+		    . ,#'mule--ucs-names-affixation)
+		   (group-function
+		    . ,(when completions-group
+			 #'mule--ucs-names-group))
 		   (category . unicode-name))
 	       (complete-with-action action (ucs-names) string pred)))))
 	 (char