Fix reported problem with drag-and-drop inside VirtualBox

* lisp/x-dnd.el (x-dnd-handle-old-kde, x-dnd-handle-offix)
(x-dnd-handle-motif): Select window before handling drop, like
on Xdnd.
(x-dnd-convert-to-offix, x-dnd-do-offix-drop)
(x-dnd-handle-unsupported-drop): Accept local selection data and
use that instead.

* src/keyboard.c (kbd_buffer_get_event): Call unsupported drop
function with local selection data as 8th arg.
* src/xselect.c (x_get_local_selection): Accept new arg
`local_value'.  All callers changed.
(Fx_get_local_selection): New function.
(syms_of_xselect): Update defsubrs.

* src/xterm.c (x_dnd_lose_ownership): New function.
(x_dnd_begin_drag_and_drop): Unless new variable is true, disown
XdndSelection after returning.  This supposedly makes
drag-and-drop from guest to host work in VirtualBox without
causing pointer motion to become choppy afterwards.
(syms_of_xterm): New variable `x_dnd_preserve_selection_data'
and update doc string of `x-dnd-unsupported-drop-function'.

* test/lisp/dnd-tests.el (dnd-tests-begin-text-drag)
(dnd-tests-begin-file-drag, dnd-tests-begin-drag-files): Set new
variable to nil during tests.

1 files changed, 7 insertions, 3 deletions

diff --git a/test/lisp/dnd-tests.el b/test/lisp/dnd-tests.el
index aae9c80273f..18dd55c206c 100644
--- a/test/lisp/dnd-tests.el
+++ b/test/lisp/dnd-tests.el
@@ -38,6 +38,7 @@
   "Alist of selection names to their values.")
 
 (defvar x-treat-local-requests-remotely)
+(defvar x-dnd-preserve-selection-data)
 
 ;; Define some replacements for functions used by the drag-and-drop
 ;; code on X when running under something else.
@@ -152,7 +153,8 @@ This function only tries to handle strings."
   ;; program with reasonably correct behavior, such as dtpad, gedit,
   ;; or Mozilla.
   ;;                ASCII            Latin-1       UTF-8
-  (let ((test-text "hello, everyone! sæl öllsömul! всем привет"))
+  (let ((test-text "hello, everyone! sæl öllsömul! всем привет")
+        (x-dnd-preserve-selection-data t))
     ;; Verify that dragging works.
     (should (eq (dnd-begin-text-drag test-text) 'copy))
     (should (eq (dnd-begin-text-drag test-text nil 'move) 'move))
@@ -187,7 +189,8 @@ This function only tries to handle strings."
         (normal-multibyte-file (expand-file-name
                                 (make-temp-name "тест-на-перетаскивание")
                                 temporary-file-directory))
-        (remote-temp-file (dnd-tests-make-temp-name)))
+        (remote-temp-file (dnd-tests-make-temp-name))
+        (x-dnd-preserve-selection-data t))
     ;; Touch those files if they don't exist.
     (unless (file-exists-p normal-temp-file)
       (write-region "" 0 normal-temp-file))
@@ -273,7 +276,8 @@ This function only tries to handle strings."
          (expand-file-name (make-temp-name "dnd-test")
                            temporary-file-directory))
         (nonexistent-remote-file (dnd-tests-make-temp-name))
-        (nonexistent-remote-file-1 (dnd-tests-make-temp-name)))
+        (nonexistent-remote-file-1 (dnd-tests-make-temp-name))
+        (x-dnd-preserve-selection-data t))
     ;; Touch those files if they don't exist.
     (unless (file-exists-p normal-temp-file)
       (write-region "" 0 normal-temp-file))