Summary: Improve sexp-based movement in message-mode

Works by giving citations and smileys a different syntax.  This helps
modes like `show-paren-mode', `electric-pair-mode', and C-M-*
sexp-based movement.

* lisp/gnus/message.el (message--syntax-propertize): New function.
(message-mode): Set syntax-related vars.
(message-smileys): New variable.

* test/automated/message-mode-tests.el: New file

lisp/gnus/message.el

@@ -2961,6 +2961,30 @@ See also `message-forbidden-properties'."
 
 (autoload 'ecomplete-setup "ecomplete") ;; for Emacs <23.
 
+(defvar message-smileys '(":-)" ":)"
+                          ":-(" ":("
+                          ";-)" ";)")
+  "A list of recognized smiley faces in `message-mode'.")
+
+(defun message--syntax-propertize (beg end)
+  "Syntax-propertize certain message text specially."
+  (let ((citation-regexp (concat "^" message-cite-prefix-regexp ".*$"))
+        (smiley-regexp (regexp-opt message-smileys)))
+    (goto-char beg)
+    (while (search-forward-regexp citation-regexp
+                                  end 'noerror)
+      (let ((start (match-beginning 0))
+            (end (match-end 0)))
+        (add-text-properties start (1+ start)
+                             `(syntax-table ,(string-to-syntax "<")))
+        (add-text-properties end (min (1+ end) (point-max))
+                             `(syntax-table ,(string-to-syntax ">")))))
+    (goto-char beg)
+    (while (search-forward-regexp smiley-regexp
+            end 'noerror)
+      (add-text-properties (match-beginning 0) (match-end 0)
+                           `(syntax-table ,(string-to-syntax "."))))))
+
 ;;;###autoload
 (define-derived-mode message-mode text-mode "Message"
   "Major mode for editing mail and news to be sent.
@@ -3063,7 +3087,13 @@ M-RET    `message-newline-and-reformat' (break the line and reformat)."
     ;; multibyte is not necessary at all. -- zsh
     (mm-enable-multibyte))
   (set (make-local-variable 'indent-tabs-mode) nil) ;No tabs for indentation.
-  (mml-mode))
+  (mml-mode)
+  ;; Syntactic fontification. Helps `show-paren-mode',
+  ;; `electric-pair-mode', and C-M-* navigation by syntactically
+  ;; excluding citations and other artifacts.
+  ;;
+  (setq-local syntax-propertize-function 'message--syntax-propertize)
+  (setq-local parse-sexp-ignore-comments t))
 
 (defun message-setup-fill-variables ()
   "Setup message fill variables."

test/automated/message-mode-tests.el

@@ -0,0 +1,55 @@
+;;; message-mode-tests.el --- Tests for message-mdoe  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2015  Free Software Foundation, Inc.
+
+;; Author: João Távora <joaotavora@gmail.com>
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This file contains tests for message-mode.
+
+;;; Code:
+(require 'ert)
+(require 'ert-x)
+
+(ert-deftest message-mode-propertize ()
+  (with-temp-buffer
+    (unwind-protect
+        (progn
+          (message-mode)
+          (insert "here's an opener (\n"
+                  "here's a sad face :-(\n"
+                  "> here's citing someone with an opener (\n"
+                  "and here's a closer ")
+          (let ((last-command-event ?\)))
+            (ert-simulate-command '(self-insert-command 1)))
+          ;; Syntax propertization doesn't kick in batch mode
+          (when noninteractive
+            (syntax-propertize (point-max)))
+          (backward-sexp)
+          (should (string= "here's an opener "
+                           (buffer-substring-no-properties
+                            (line-beginning-position)
+                            (point))))
+          (forward-sexp)
+          (should (string= "and here's a closer )"
+                           (buffer-substring-no-properties
+                            (line-beginning-position)
+                            (point)))))
+      (set-buffer-modified-p nil))))
+
+(provide 'message-mode-tests)
+;;; message-mode-tests.el ends here