bug#26599: patch for mwheel.el

[Tak Kunihiro]

To utilize both horizontal and vertical scrolling by touchpad, I
locally turn off auto-hscroll-mode during wheel scrolling using
advice-add.

  (advice-add 'mwheel-scroll :before 'touchpad-mode)

Is it possible to add a line that runs hook on `mwheel.el' to let me
do so without advice-add?

In `(emacs) Coding Standards', to avoid using ‘defadvice’ is
implicitly suggested.  Adding the line lets me implement
`touchpad-mode' which makes swiping touchpad scroll horizontally and
vertically, in cleaner fashion (without any side effects, I think).


diff -u "c:/Users/dream/.emacs.d/site-lisp/mwheel.20170410.el" 
"c:/Users/dream/.emacs.d/site-lisp/mwheel.el"
--- c:/Users/dream/.emacs.d/site-lisp/mwheel.20170410.el        2017-04-21 
09:28:22.949364100 +0900
+++ c:/Users/dream/.emacs.d/site-lisp/mwheel.el 2017-04-21 21:19:46.792800400 
+0900
@@ -148,6 +148,12 @@
   :group 'mouse
   :type 'boolean)
 
+(defcustom mwheel-pre-scroll-hook nil
+  "A hook that gets run just before scrolling by wheel."
+  :group 'mouse
+  :type 'hook
+  :version "26.1")
+
 (eval-and-compile
   (if (fboundp 'event-button)
       (fset 'mwheel-event-button 'event-button)
@@ -232,6 +238,7 @@
       ;; When the double-mouse-N comes in, a mouse-N has been executed already,
       ;; So by adding things up we get a squaring up (1, 3, 6, 10, 15, ...).
       (setq amt (* amt (event-click-count event))))
+    (run-hooks 'mwheel-pre-scroll-hook)
     (unwind-protect
        (let ((button (mwheel-event-button event)))
          (cond ((eq button mouse-wheel-down-event)
@@ -320,7 +327,6 @@
   "Enable mouse wheel support."
   (mouse-wheel-mode (if uninstall -1 1)))
 
-
 ;;; For tilt-scroll
 ;;;
 (defcustom mwheel-tilt-scroll-p nil