bug#4623: 23.1.50; rmail changes encoding of characters on save

[Eli Zaretskii]

> Date: Mon, 07 Dec 2009 06:04:34 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 4623@emacsbugs.donarmstrong.com
> 
> > From: Markus Rost <rost@math.uni-bielefeld.de>
> > CC: 4623@emacsbugs.donarmstrong.com
> > Date: Sun,  6 Dec 2009 21:23:48 +0100 (CET)
> > 
> > One minor thing:  Since rmail-message-encoding is a global variable,
> > several Rmail buffers may interfere.
> 
> Right, I didn't think abut that possibility.  I will try to think
> about some simple solution.

I think I found it.

If we have to live with rmail-write-region-annotate, we might as well
have it do something useful:

Index: lisp/mail/rmail.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/mail/rmail.el,v
retrieving revision 1.562
diff -u -r1.562 rmail.el
--- lisp/mail/rmail.el  4 Dec 2009 05:00:47 -0000       1.562
+++ lisp/mail/rmail.el  7 Dec 2009 19:14:23 -0000
@@ -1316,13 +1316,19 @@
 This function preserves the current buffer's modified flag, and also
 sets the current buffer's `buffer-file-coding-system' to that of
 `rmail-view-buffer'."
-  (let ((modp (buffer-modified-p))
-       (coding
+  (let ((modp-this (buffer-modified-p))
+       (modp-that
+        (with-current-buffer rmail-view-buffer (buffer-modified-p)))
+       (coding-this buffer-file-coding-system)
+       (coding-that
         (with-current-buffer rmail-view-buffer
           buffer-file-coding-system)))
     (buffer-swap-text rmail-view-buffer)
-    (setq buffer-file-coding-system coding)
-    (restore-buffer-modified-p modp)))
+    (setq buffer-file-coding-system coding-that)
+    (with-current-buffer rmail-view-buffer
+      (setq buffer-file-coding-system coding-this)
+      (restore-buffer-modified-p modp-that))
+    (restore-buffer-modified-p modp-this)))
 
 (defun rmail-buffers-swapped-p ()
   "Return non-nil if the message collection is in `rmail-view-buffer'."
@@ -4179,16 +4185,31 @@
 (add-to-list 'desktop-buffer-mode-handlers
             '(rmail-mode . rmail-restore-desktop-buffer))
 
+;; We use this to record the encoding of the current message before
+;; saving the message collection.
+(defvar rmail-message-encoding nil)
+
 ;; Used in `write-region-annotate-functions' to write rmail files.
 (defun rmail-write-region-annotate (start end)
   (when (and (null start) (rmail-buffers-swapped-p))
+    (setq rmail-message-encoding buffer-file-coding-system)
     (set-buffer rmail-view-buffer)
-    ;; Prevent viewing different messages from messing up the coding. 
(Bug#4623)
-    ;; FIXME is there a better solution?
-    (set (make-local-variable 'coding-system-for-write) 'no-conversion)
     (widen)
     nil))
 
+;; Used to restore the encoding of the buffer where we show the
+;; current message, after we save the message collection.  This is
+;; needed because rmail-write-region-annotate switches buffers behind
+;; save-file's back, with the side effect that last-coding-system-used
+;; is assigned to buffer-file-coding-system of the wrong buffer.
+(defun rmail-after-save-hook ()
+  (if (or (eq rmail-view-buffer (current-buffer))
+         (eq rmail-buffer (current-buffer)))
+      (with-current-buffer
+         (if (rmail-buffers-swapped-p) rmail-buffer rmail-view-buffer)
+       (setq buffer-file-coding-system rmail-message-encoding))))
+(add-hook 'after-save-hook 'rmail-after-save-hook)
+
 
 ;;; Start of automatically extracted autoloads.