Add support for dragging text from Emacs to other programs

This still probably needs some more protection from
malfunctioning clients which delete windows at random, but I
don't know if that's a problem in practice.

* doc/emacs/frames.texi (Drag and Drop):
* doc/lispref/frames.texi (Drag and Drop): Document new
features.

* etc/NEWS: Announce new function `x-begin-drag' and new user
option `mouse-drag-and-drop-region-cross-program'.

* lisp/mouse.el (mouse-drag-and-drop-region-cross-program): New
user option.
(x-begin-drag): New variable declaration.
(mouse-drag-and-drop-region): If the mouse moves out of an Emacs
frame, begin a window system drag.
* lisp/x-dnd.el (x-dnd-handle-xdnd): Remove left-over debugging
code.

* src/xfns.c (Fx_set_mouse_absolute_pixel_position): Fix
indentation of opening paren.
(Fx_begin_drag): New function.
(syms_of_xfns): Define new subr.
* src/xselect.c (x_timestamp_for_selection): New function.

* src/xterm.c (X_DND_SUPPORTED_VERSION): New preprocessor
declaration.
(x_dnd_get_window_proto, x_dnd_send_enter, x_dnd_send_position)
(x_dnd_send_leave, x_dnd_send_drop, x_set_dnd_targets)
(x_dnd_begin_drag_and_drop): New functions.
(handle_one_xevent): Handle drag-and-drop motion and button
events when active.
(x_free_frame_resources): If f is the DND source, stop
drag-and-drop.
(x_term_init): Intern new atoms.
(syms_of_xterm): New symbol QXdndSelection.

* src/xterm.h (struct x_display_info): New atoms
Xatom_XdndAware, Xatom_XdndSelection, Xatom_XdndTypeList,
Xatom_XdndActionCopy, Xatom_XdndActionMove,
Xatom_XdndActionLink, Xatom_XdndActionAsk,
Xatom_XdndActionPrivate, Xatom_XdndActionList,
Xatom_XdndActionDescription, Xatom_XdndProxy, Xatom_XdndEnter,
Xatom_XdndPosition, Xatom_XdndStatus, Xatom_XdndLeave,
Xatom_XdndDrop, and Xatom_XdndFinished.

1 files changed, 10 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index d6b5da3902e..f4d8756950b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -170,6 +170,11 @@ methods instead.
 * Changes in Emacs 29.1
 
 +++
+** New user option 'mouse-drag-and-drop-region-cross-program'.
+If non-nil, this option allows dragging text in the region from Emacs
+to another program.
+
++++
 ** New function 'command-query'.
 This function makes its argument command prompt the user for
 confirmation before executing.
@@ -1203,6 +1208,11 @@ functions.
 
 * Lisp Changes in Emacs 29.1
 
++++
+** New function 'x-begin-drag'.
+This function initiates a drag-and-drop request with the contents of
+the selection 'XdndSelection', and returns when a drop occurs.
+
 ---
 ** New function 'ietf-drums-parse-date-string'.
 This function parses RFC5322 (and RFC822) date strings, and should be