Add and use function horizontal-scroll-bars-available-p.

* scroll-bar.el (horizontal-scroll-bars-available-p): New
function.
(horizontal-scroll-bar-mode): Rewrite using
horizontal-scroll-bars-available-p.
* menu-bar.el (menu-bar-showhide-scroll-bar-menu): Rewrite using
horizontal-scroll-bars-available-p.

4 files changed, 37 insertions, 16 deletions

diff --git a/etc/NEWS b/etc/NEWS
index bdda3ed0672..3b7516dd819 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -240,6 +240,8 @@ optional repeat-count argument.
 ** Emacs can now draw horizontal scroll bars on some platforms that
 provide toolkit scroll bars, namely Gtk, Lucid, Motif and Windows.
 Horizontal scroll bars are turned off by default.
+*** New function `horizontal-scroll-bars-available-p' telling whether
+    horizontal scroll bars are available on the underlying system.
 *** New mode `horizontal-scroll-bar-mode' to toggle horizontal scroll
     bars on all existing and future frames.
 *** New frame parameters `horizontal-scroll-bars' and
diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 2cc27412da4..c6469006b81 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,12 @@
+2014-09-05  Martin Rudalics  <rudalics@gmx.at>
+
+        * scroll-bar.el (horizontal-scroll-bars-available-p): New
+        function.
+        (horizontal-scroll-bar-mode): Rewrite using
+        horizontal-scroll-bars-available-p.
+        * menu-bar.el (menu-bar-showhide-scroll-bar-menu): Rewrite using
+        horizontal-scroll-bars-available-p.
+
 2014-09-05  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * subr.el (call-process-shell-command, process-file-shell-command):
diff --git a/lisp/menu-bar.el b/lisp/menu-bar.el
index 57acbbe648e..9657c5924f9 100644
--- a/lisp/menu-bar.el
+++ b/lisp/menu-bar.el
@@ -903,19 +903,17 @@ by \"Save Options\" in Custom buffers.")
       '(menu-item "Horizontal"
                   menu-bar-horizontal-scroll-bar
                   :help "Horizontal scroll bar"
-                  :visible (display-graphic-p)
-                  :button (:radio . (eq (cdr (assq 'horizontal-scroll-bars
-                                                   (frame-parameters)))
-                                        t))))
+                  :visible (horizontal-scroll-bars-available-p)
+                  :button (:radio . (cdr (assq 'horizontal-scroll-bars
+                                               (frame-parameters))))))
 
     (bindings--define-key menu [none-horizontal]
       '(menu-item "None-horizontal"
                   menu-bar-no-horizontal-scroll-bar
                   :help "Turn off horizontal scroll bars"
-                  :visible (display-graphic-p)
-                  :button (:radio . (eq (cdr (assq 'horizontal-scroll-bars
-                                                   (frame-parameters)))
-                                        nil))))
+                  :visible (horizontal-scroll-bars-available-p)
+                  :button (:radio . (not (cdr (assq 'horizontal-scroll-bars
+                                                   (frame-parameters)))))))
 
     (bindings--define-key menu [right]
       '(menu-item "On the Right"
diff --git a/lisp/scroll-bar.el b/lisp/scroll-bar.el
index 588ac3b0f8a..63713c24a64 100644
--- a/lisp/scroll-bar.el
+++ b/lisp/scroll-bar.el
@@ -144,6 +144,13 @@ created in the future."
                             (if v (or previous-scroll-bar-mode
                                       default-frame-scroll-bars))))))
 
+(defun horizontal-scroll-bars-available-p ()
+  "Return non-nil when horizontal scroll bars are available on this system."
+  (and (display-graphic-p)
+       (boundp 'x-toolkit-scroll-bars)
+       x-toolkit-scroll-bars
+       (not (eq (window-system) 'ns))))
+
 (define-minor-mode horizontal-scroll-bar-mode
   "Toggle horizontal scroll bars on all frames (Horizontal Scroll Bar mode).
 With a prefix argument ARG, enable Horizontal Scroll Bar mode if
@@ -155,14 +162,19 @@ created in the future."
   :init-value nil
   :global t
   :group 'frames
-  (dolist (frame (frame-list))
-    (set-frame-parameter
-     frame 'horizontal-scroll-bars horizontal-scroll-bar-mode))
-  ;; Handle `default-frame-alist' entry.
-  (setq default-frame-alist
-        (cons (cons 'horizontal-scroll-bars horizontal-scroll-bar-mode)
-              (assq-delete-all 'horizontal-scroll-bars
-                               default-frame-alist))))
+  (if (and horizontal-scroll-bar-mode
+           (not (horizontal-scroll-bars-available-p)))
+      (progn
+        (setq horizontal-scroll-bar-mode nil)
+        (message "Horizontal scroll bars are not implemented on this system"))
+    (dolist (frame (frame-list))
+      (set-frame-parameter
+       frame 'horizontal-scroll-bars horizontal-scroll-bar-mode))
+    ;; Handle `default-frame-alist' entry.
+    (setq default-frame-alist
+          (cons (cons 'horizontal-scroll-bars horizontal-scroll-bar-mode)
+                (assq-delete-all 'horizontal-scroll-bars
+                                 default-frame-alist)))))
 
 (defun toggle-scroll-bar (arg)
   "Toggle whether or not the selected frame has vertical scroll bars.