Allow dragging and dropping multiple actions

* doc/lispref/frames.texi (Drag and Drop): Document new meaning
of `action'.
* lisp/term/haiku-win.el (x-begin-drag): Correct for new meaning
of `action'.
* src/xfns.c (Fx_begin_drag): Handle new alist meaning of
`action'.
* src/xterm.c (x_dnd_begin_drag_and_drop): New parameters
`ask_action_list', `ask_action_names' and `n_ask_actions'.
* src/xterm.h: Update prototypes.

doc/lispref/frames.texi

@@ -4061,6 +4061,11 @@ the drop target; or @code{XdndActionMove}, which means copy as with
 @code{XdndActionCopy}, and in addition the caller should delete
 whatever was stored in that selection after copying it.
 
+@var{action} may also be an alist which associates between symbols
+describing the available actions, and strings that the drop target is
+expected to present to the user to choose between the available
+actions.
+
 If @var{return-frame} is non-nil and the mouse moves over an Emacs
 frame after first moving out of @var{frame}, then the frame to which
 the mouse moves will be returned immediately.  This is useful when you

lisp/term/haiku-win.el

@@ -224,7 +224,9 @@ take effect on menu items until the menu bar is updated again."
               (push (cadr selection-result)
                     (cdr (alist-get (car selection-result) message
                                     nil nil #'equal))))))))
-    (prog1 (or action 'XdndActionCopy)
+    (prog1 (or (and (symbolp action)
+                    action)
+               'XdndActionCopy)
       (haiku-drag-message (or frame (selected-frame))
                           message))))
 

src/xfns.c

@@ -6614,17 +6614,28 @@ If RETURN-FRAME is non-nil, this function will return the frame if the
 mouse pointer moves onto an Emacs frame, after first moving out of
 FRAME.
 
+If ACTION is a list and not nil, its elements are assumed to be a cons
+of (ITEM . STRING), where ITEM is the name of an action, and STRING is
+a string describing ITEM to the user.  The drop target is expected to
+prompt the user to choose between any of the actions in the list.
+
 If ACTION is not specified or nil, `XdndActionCopy' is used
 instead.  */)
   (Lisp_Object targets, Lisp_Object action, Lisp_Object frame,
    Lisp_Object return_frame)
 {
   struct frame *f = decode_window_system_frame (frame);
-  int ntargets = 0;
+  int ntargets = 0, nnames = 0;
+  ptrdiff_t len;
   char *target_names[2048];
   Atom *target_atoms;
-  Lisp_Object lval, original;
+  Lisp_Object lval, original, tem, t1, t2;
   Atom xaction;
+  Atom action_list[2048];
+  char *name_list[2048];
+  char *scratch;
+
+  USE_SAFE_ALLOCA;
 
   CHECK_LIST (targets);
   original = targets;
@@ -6650,10 +6661,48 @@ instead.  */)
     xaction = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionMove;
   else if (EQ (action, QXdndActionLink))
     xaction = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionLink;
-  else if (EQ (action, QXdndActionAsk))
-    xaction = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionAsk;
   else if (EQ (action, QXdndActionPrivate))
     xaction = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionPrivate;
+  else if (CONSP (action))
+    {
+      xaction = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionAsk;
+      original = action;
+
+      CHECK_LIST (action);
+      for (; CONSP (action); action = XCDR (action))
+	{
+	  tem = XCAR (action);
+	  CHECK_CONS (tem);
+	  t1 = XCAR (tem);
+	  t2 = XCDR (tem);
+	  CHECK_SYMBOL (t1);
+	  CHECK_STRING (t2);
+
+	  if (nnames < 2048)
+	    {
+	      if (EQ (t1, QXdndActionCopy))
+		action_list[nnames] = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionCopy;
+	      else if (EQ (t1, QXdndActionMove))
+		action_list[nnames] = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionMove;
+	      else if (EQ (t1, QXdndActionLink))
+		action_list[nnames] = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionLink;
+	      else if (EQ (t1, QXdndActionPrivate))
+		action_list[nnames] = FRAME_DISPLAY_INFO (f)->Xatom_XdndActionPrivate;
+	      else
+		signal_error ("Invalid drag-and-drop action", tem);
+
+	      scratch = SSDATA (ENCODE_UTF_8 (t2));
+	      len = strlen (scratch);
+	      name_list[nnames] = SAFE_ALLOCA (len + 1);
+	      strncpy (name_list[nnames], scratch, len + 1);
+
+	      nnames++;
+	    }
+	  else
+	    error ("Too many actions");
+	}
+      CHECK_LIST_END (action, original);
+    }
   else
     signal_error ("Invalid drag-and-drop action", action);
 
@@ -6666,8 +6715,10 @@ instead.  */)
 
   x_set_dnd_targets (target_atoms, ntargets);
   lval = x_dnd_begin_drag_and_drop (f, FRAME_DISPLAY_INFO (f)->last_user_time,
-				    xaction, !NILP (return_frame));
+				    xaction, !NILP (return_frame), action_list,
+				    (const char **) &name_list, nnames);
 
+  SAFE_FREE ();
   return lval;
 }
 

src/xterm.c

@@ -6942,7 +6942,9 @@ x_top_window_to_frame (struct x_display_info *dpyinfo, int wdesc)
 
 Lisp_Object
 x_dnd_begin_drag_and_drop (struct frame *f, Time time, Atom xaction,
-			   bool return_frame_p)
+			   bool return_frame_p, Atom *ask_action_list,
+			   const char **ask_action_names,
+			   size_t n_ask_actions)
 {
 #ifndef USE_GTK
   XEvent next_event;
@@ -6951,9 +6953,11 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time time, Atom xaction,
   XWindowAttributes root_window_attrs;
   struct input_event hold_quit;
   struct frame *any;
-  char *atom_name;
+  char *atom_name, *ask_actions;
   Lisp_Object action, ltimestamp;
   specpdl_ref ref;
+  ptrdiff_t i, end, fill;
+  XTextProperty prop;
 
   if (!FRAME_VISIBLE_P (f))
     error ("Frame is invisible");
@@ -6972,6 +6976,41 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time time, Atom xaction,
   else
     x_dnd_selection_timestamp = XFIXNUM (ltimestamp);
 
+  if (n_ask_actions)
+    {
+      ask_actions = NULL;
+      end = 0;
+
+      for (i = 0; i < n_ask_actions; ++i)
+	{
+	  fill = end;
+	  end += strlen (ask_action_names[i]) + 1;
+
+	  if (ask_actions)
+	    ask_actions = xrealloc (ask_actions, end);
+	  else
+	    ask_actions = xmalloc (end);
+
+	  strncpy (ask_actions + fill,
+		   ask_action_names[i],
+		   end - fill);
+	}
+
+      prop.value = (unsigned char *) ask_actions;
+      prop.encoding = XA_STRING;
+      prop.format = 8;
+      prop.nitems = end;
+
+      XSetTextProperty (FRAME_X_DISPLAY (f), FRAME_X_WINDOW (f),
+			&prop, FRAME_DISPLAY_INFO (f)->Xatom_XdndActionDescription);
+      xfree (ask_actions);
+
+      XChangeProperty (FRAME_X_DISPLAY (f), FRAME_X_WINDOW (f),
+		       FRAME_DISPLAY_INFO (f)->Xatom_XdndActionList, XA_ATOM, 32,
+		       PropModeReplace, (unsigned char *) ask_action_list,
+		       n_ask_actions);
+    }
+
   x_dnd_in_progress = true;
   x_dnd_frame = f;
   x_dnd_last_seen_window = FRAME_X_WINDOW (f);

src/xterm.h

@@ -1373,7 +1373,8 @@ extern void x_scroll_bar_configure (GdkEvent *);
 #endif
 
 extern Lisp_Object x_dnd_begin_drag_and_drop (struct frame *, Time, Atom,
-					      bool);
+					      bool, Atom *, const char **,
+					      size_t);
 extern void x_set_dnd_targets (Atom *, int);
 
 INLINE int