Handle virtual modifiers in the DND scrolling code

* lisp/x-dnd.el (x-dnd-modifier-mask): Handle virtual modifiers.
* src/xfns.c (Fx_get_modifier_masks): New function.
(syms_of_xfns): Define new subr.
* src/xterm.c (x_get_keyboard_modifiers): New function.
* src/xterm.h: Update prototypes.

lisp/x-dnd.el

@@ -696,19 +696,30 @@ with coordinates relative to the root window."
   "Return the nmore-than3 bit from the 32 bit FLAGS in an XDndEnter message."
   (logand flags 1))
 
+(declare-function x-get-modifier-masks "xfns.c")
+
 (defun x-dnd-modifier-mask (mods)
   "Return the X modifier mask for the Emacs modifier state MODS.
 MODS is a single symbol, or a list of symbols such as `shift' or
 `control'."
-  (let ((mask 0))
+  (let ((virtual-modifiers (x-get-modifier-masks))
+        (mask 0))
     (unless (consp mods)
       (setq mods (list mods)))
     (dolist (modifier mods)
       ;; TODO: handle virtual modifiers such as Meta and Hyper.
       (cond ((eq modifier 'shift)
-             (setq mask (logior mask 1)))   ; ShiftMask
+             (setq mask (logior mask 1))) ; ShiftMask
             ((eq modifier 'control)
-             (setq mask (logior mask 4))))) ; ControlMask
+             (setq mask (logior mask 4))) ; ControlMask
+            ((eq modifier 'meta)
+             (setq mask (logior mask (nth 4 virtual-modifiers))))
+            ((eq modifier 'hyper)
+             (setq mask (car virtual-modifiers)))
+            ((eq modifier 'super)
+             (setq mask (cadr virtual-modifiers)))
+            ((eq modifier 'alt)
+             (setq mask (nth 2 virtual-modifiers)))))
     mask))
 
 (defun x-dnd-hscroll-flags ()

src/xfns.c

@@ -9426,6 +9426,24 @@ present and mapped to the usual X keysyms.  */)
 #endif
 }
 
+DEFUN ("x-get-modifier-masks", Fx_get_modifier_masks, Sx_get_modifier_masks,
+       0, 1, 0,
+       doc: /* Return the X modifier masks corresponding to keyboard modifiers.
+The optional second argument TERMINAL specifies which display to fetch
+modifier masks from.  TERMINAL should be a terminal object, a frame or
+a display name (a string).  If TERMINAL is omitted or nil, that stands
+for the selected frame's display.
+
+Return a list of (HYPER SUPER ALT SHIFT-LOCK META), each element being
+a number describing the modifier mask for the corresponding Emacs
+modifier.  */)
+  (Lisp_Object terminal)
+{
+  struct x_display_info *dpyinfo;
+
+  dpyinfo = check_x_display_info (terminal);
+  return x_get_keyboard_modifiers (dpyinfo);
+}
 
 
 /***********************************************************************
@@ -10090,6 +10108,7 @@ eliminated in future versions of Emacs.  */);
   defsubr (&Sx_begin_drag);
   defsubr (&Sx_display_set_last_user_time);
   defsubr (&Sx_translate_coordinates);
+  defsubr (&Sx_get_modifier_masks);
 
   tip_timer = Qnil;
   staticpro (&tip_timer);

src/xterm.c

@@ -28187,6 +28187,27 @@ x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost,
     }
 }
 
+/* Return a list of the keyboard modifier masks in DPYINFO.
+
+   Value is a list of (HYPER SUPER ALT SHIFT-LOCK META), each element
+   being the appropriate modifier mask.  */
+
+Lisp_Object
+x_get_keyboard_modifiers (struct x_display_info *dpyinfo)
+{
+  /* This sometimes happens when the function is called during display
+     initialization, which can happen while obtaining vendor specific
+     keysyms.  */
+  if (!dpyinfo->xkb_desc && !dpyinfo->modmap)
+    x_find_modifier_meanings (dpyinfo);
+
+  return list5 (make_uint (dpyinfo->hyper_mod_mask),
+		make_uint (dpyinfo->super_mod_mask),
+		make_uint (dpyinfo->alt_mod_mask),
+		make_uint (dpyinfo->shift_lock_mask),
+		make_uint (dpyinfo->meta_mod_mask));
+}
+
 void
 syms_of_xterm (void)
 {

src/xterm.h

@@ -1645,6 +1645,7 @@ extern bool x_defined_color (struct frame *, const char *, Emacs_Color *,
                              bool, bool);
 extern void x_preserve_selections (struct x_display_info *, Lisp_Object,
 				   Lisp_Object);
+extern Lisp_Object x_get_keyboard_modifiers (struct x_display_info *);
 #ifdef HAVE_X_I18N
 extern void free_frame_xic (struct frame *);
 # if defined HAVE_X_WINDOWS && defined USE_X_TOOLKIT