Add a major-mode for the *Messages* buffer

Ref: http://lists.gnu.org/archive/html/emacs-devel/2010-02/msg00135.html

* lisp/simple.el (messages-buffer-mode): New major mode.
(messages-buffer): New function.

* lisp/startup.el (normal-top-level): Switch mode of *Messages* buffer.

* src/xdisp.c (message_dolog): If we create *Messages*,
switch it to messages-buffer-mode.

* lisp/emacs-lisp/ert.el (ert--force-message-log-buffer-truncation)
(ert-run-test): Use `message-buffer' function.
(ert--force-message-log-buffer-truncation): Ignore read-only.

* lisp/help.el (view-echo-area-messages): Use `message-buffer' function.

* lisp/mail/emacsbug.el (report-emacs-bug): Use `message-buffer' function.

* lisp/gnus/gnus-util.el (gnus-message-with-timestamp-1):
Use `message-buffer' function if available.  Ignore read-only.

* etc/NEWS: Mention this.

2 files changed, 20 insertions, 3 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b4ec77780e4..00b59e89e67 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2013-09-17  Glenn Morris  <rgm@gnu.org>
+
+        * xdisp.c (message_dolog): If we create *Messages*,
+        switch it to messages-buffer-mode.
+
 2013-09-17  Paul Eggert  <eggert@cs.ucla.edu>
 
         Don't overuse 'const' in types of locals.
diff --git a/src/xdisp.c b/src/xdisp.c
index 4582002fa0e..b07aad51bc9 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -1,7 +1,6 @@
 /* Display generation from window structure and buffer text.
 
-Copyright (C) 1985-1988, 1993-1995, 1997-2013 Free Software Foundation,
-Inc.
+Copyright (C) 1985-1988, 1993-1995, 1997-2013 Free Software Foundation, Inc.
 
 This file is part of GNU Emacs.
 
@@ -9538,7 +9537,20 @@ message_dolog (const char *m, ptrdiff_t nbytes, bool nlflag, bool multibyte)
 
       old_deactivate_mark = Vdeactivate_mark;
       oldbuf = current_buffer;
-      Fset_buffer (Fget_buffer_create (Vmessages_buffer_name));
+
+      /* Ensure the Messages buffer exists, and switch to it.
+         If we created it, set the major-mode.  */
+      {
+        int newbuffer = 0;
+        if (NILP (Fget_buffer (Vmessages_buffer_name))) newbuffer = 1;
+
+        Fset_buffer (Fget_buffer_create (Vmessages_buffer_name));
+
+        if (newbuffer &&
+            !NILP (Ffboundp (intern ("messages-buffer-mode"))))
+          call0 (intern ("messages-buffer-mode"));
+      }
+
       bset_undo_list (current_buffer, Qt);
 
       oldpoint = message_dolog_marker1;