bug#8308: 23.3; Use utf-8 for writing abbrev file

[Leo <sdl.web@gmail.com>]

On 2011-03-22 10:48 +0800, Stefan Monnier wrote:
> I think it might be OK to do it for Emacs-25, but since Emacs-22 can't
> handle utf-8-emacs, I think it's a bit early to switch to it in
> Emacs-24.  If utf-8 is sufficient, OTOH it's the best choice.  So maybe
> we should check the buffer first to see if utf-8 is safe, and only fall
> back to emacs-mule if utf-8 is not safe.

I think default to utf-8 is good, which is sufficient for most people.
Any comments on the following patch? I don't know how to introduce a
char unencodable with utf-8 to the abbrevs. So it is only partially
tested.


=== modified file 'lisp/abbrev.el'
--- lisp/abbrev.el	2011-01-25 04:08:28 +0000
+++ lisp/abbrev.el	2011-03-22 03:30:52 +0000
@@ -225,21 +225,29 @@
 		    abbrev-file-name)))
   (or (and file (> (length file) 0))
       (setq file abbrev-file-name))
-  (let ((coding-system-for-write 'emacs-mule))
-    (with-temp-file file
-      (insert ";;-*-coding: emacs-mule;-*-\n")
+  (let ((coding-system-for-write 'utf-8))
+    (with-temp-buffer
       (dolist (table
-               ;; We sort the table in order to ease the automatic
-               ;; merging of different versions of the user's abbrevs
-               ;; file.  This is useful, for example, for when the
-               ;; user keeps their home directory in a revision
-               ;; control system, and is therefore keeping multiple
-               ;; slightly-differing copies loosely synchronized.
-               (sort (copy-sequence abbrev-table-name-list)
-                     (lambda (s1 s2)
-                       (string< (symbol-name s1)
-                                (symbol-name s2)))))
-	(insert-abbrev-table-description table nil)))))
+	       ;; We sort the table in order to ease the automatic
+	       ;; merging of different versions of the user's abbrevs
+	       ;; file.  This is useful, for example, for when the
+	       ;; user keeps their home directory in a revision
+	       ;; control system, and is therefore keeping multiple
+	       ;; slightly-differing copies loosely synchronized.
+	       (sort (copy-sequence abbrev-table-name-list)
+		     (lambda (s1 s2)
+		       (string< (symbol-name s1)
+				(symbol-name s2)))))
+	(insert-abbrev-table-description table nil))
+      (when (unencodable-char-position (point-min) (point-max) 'utf-8)
+	(setq coding-system-for-write
+	      (if (> emacs-major-version 24)
+		  'utf-8-emacs
+		;; For compatibility with Emacs 22
+		'emacs-mule)))
+      (goto-char (point-min))
+      (insert (format ";;-*-coding: %s;-*-\n" coding-system-for-write))
+      (write-region nil nil file nil 0))))
 \f
 (defun add-mode-abbrev (arg)
   "Define mode-specific abbrev for last word(s) before point.