master 833767e53f: Disable middle click selection emulation during XDS

[Po Lu]

branch: master
commit 833767e53fcb55e3000b54de1cb3803900c363e9
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Disable middle click selection emulation during XDS
    
    * doc/lispref/frames.texi (Drag and Drop): Document new
    variable.
    * lisp/x-dnd.el (x-dnd-do-direct-save): Disable drop emulation
    during XDS drag-and-drop.
    
    * src/keyboard.c (kbd_buffer_get_event): Handle recorded value.
    * src/xterm.c (x_dnd_do_unsupported_drop): Return if new
    variable is nil.
    (x_dnd_send_unsupported_drop): Record value of new variable in
    events.
    (x_dnd_begin_drag_and_drop): Handle recorded value.
    (syms_of_xterm): New variable `x-dnd-use-unsupported-drop'.
---
 doc/lispref/frames.texi | 12 ++++++++++++
 lisp/x-dnd.el           |  2 ++
 src/keyboard.c          |  5 ++++-
 src/xterm.c             | 20 +++++++++++++++++---
 4 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 720753edad..f7491502f4 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -4280,6 +4280,18 @@ will only be used if @code{"FILE_NAME"} is one of the 
targets given to
 to drop all supported content.
 @end defvar
 
+@defvar x-dnd-use-unsupported-drop
+When one of the @code{"STRING"}, @code{"UTF8_STRING"},
+@code{"COMPOUND_TEXT"} or @code{"TEXT"} targets is present in the list
+given to @code{x-begin-drag}, Emacs will try to use synthesized mouse
+events and the primary selection to insert the text if the drop target
+doesn't support any drag-and-drop protocol at all.
+
+A side effect is that Emacs will become the owner of the primary
+selection upon such a drop.  If that is not desired, then the drop
+emulation can be disabled by setting this variable to @code{nil}.
+@end defvar
+
 @node Color Names
 @section Color Names
 
diff --git a/lisp/x-dnd.el b/lisp/x-dnd.el
index c3d56f327d..43905e1bb0 100644
--- a/lisp/x-dnd.el
+++ b/lisp/x-dnd.el
@@ -1144,6 +1144,7 @@ ACTION is the action given to `x-begin-drag'."
   "Whether or not the drop target made a request for `XdndDirectSave0'.")
 
 (defvar x-dnd-disable-motif-protocol)
+(defvar x-dnd-use-unsupported-drop)
 
 (defun x-dnd-handle-direct-save (_selection _type _value)
   "Handle a selection request for `XdndDirectSave'."
@@ -1204,6 +1205,7 @@ was taken, or the direct save failed."
         ;; possibly work with Motif or OffiX programs.
         (x-dnd-disable-motif-protocol t)
         (x-dnd-use-offix-drop nil)
+        (x-dnd-use-unsupported-drop nil)
         (prop-deleted nil)
         encoded-name)
     (unwind-protect
diff --git a/src/keyboard.c b/src/keyboard.c
index 8b8d348c41..4cac20eb4b 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -4068,7 +4068,10 @@ kbd_buffer_get_event (KBOARD **kbp,
 
          /* `x-dnd-unsupported-drop-function' could have deleted the
             event frame.  */
-         if (!FRAME_LIVE_P (f))
+         if (!FRAME_LIVE_P (f)
+             /* This means `x-dnd-use-unsupported-drop' was nil when the
+                event was generated.  */
+             || NILP (XCAR (XCDR (XCDR (XCDR (event->ie.arg))))))
            break;
 
          x_dnd_do_unsupported_drop (FRAME_DISPLAY_INFO (f),
diff --git a/src/xterm.c b/src/xterm.c
index 500443ebaa..fa43371f05 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -3810,6 +3810,9 @@ x_dnd_do_unsupported_drop (struct x_display_info *dpyinfo,
   if (NILP (value))
     return;
 
+  if (!x_dnd_use_unsupported_drop)
+    return;
+
   event.xbutton.serial = 0;
   event.xbutton.send_event = True;
   event.xbutton.display = dpyinfo->display;
@@ -3914,9 +3917,10 @@ x_dnd_send_unsupported_drop (struct x_display_info 
*dpyinfo, Window target_windo
   ie.kind = UNSUPPORTED_DROP_EVENT;
   ie.code = (unsigned) target_window;
   ie.modifiers = x_dnd_unsupported_event_level;
-  ie.arg = list3 (assq_no_quit (QXdndSelection,
+  ie.arg = list4 (assq_no_quit (QXdndSelection,
                                dpyinfo->terminal->Vselection_alist),
-                 targets, arg);
+                 targets, arg, (x_dnd_use_unsupported_drop
+                                ? Qt : Qnil));
   ie.timestamp = before;
 
   XSETINT (ie.x, root_x);
@@ -11377,7 +11381,10 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time time, 
Atom xaction,
 
       /* `x-dnd-unsupported-drop-function' could have deleted the
         event frame.  */
-      if (!FRAME_LIVE_P (event_frame))
+      if (!FRAME_LIVE_P (event_frame)
+         /* This means `x-dnd-use-unsupported-drop' was nil when the
+            event was generated.  */
+         || NILP (XCAR (XCDR (XCDR (XCDR (event->ie.arg))))))
        continue;
 
       x_dnd_do_unsupported_drop (FRAME_DISPLAY_INFO (event_frame),
@@ -28075,4 +28082,11 @@ drag-and-drop code.  */);
 When non-nil, `x-begin-drag' will not drop onto any window that only
 supports the Motif drag-and-drop protocols.  */);
   x_dnd_disable_motif_protocol = false;
+
+  DEFVAR_BOOL ("x-dnd-use-unsupported-drop", x_dnd_use_unsupported_drop,
+    doc: /* Enable the emulation of drag-and-drop based on the primary 
selection.
+When nil, do not use the primary selection and synthetic mouse clicks
+to emulate the drag-and-drop of `STRING', `UTF8_STRING',
+`COMPOUND_TEXT' or `TEXT'.  */);
+  x_dnd_use_unsupported_drop = true;
 }