Fix region display while dragging mouse

* lisp/mouse.el (mouse-drag-track): Reset deactivate-mark in the
buffer of the drag event, to allow mark to be set and the region
be shown as we drag the mouse.  (Bug#24030)

This was backported from master
(cherry picked from commit 7d58b02f363ab02961faa950d1ba727df96f2f19)

1 files changed, 5 insertions, 3 deletions

diff --git a/lisp/mouse.el b/lisp/mouse.el
index d0694007d56..699225277de 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -808,14 +808,16 @@ The region will be defined with mark and point."
   (setq mouse-selection-click-count-buffer (current-buffer))
   (deactivate-mark)
   (let* ((scroll-margin 0) ; Avoid margin scrolling (Bug#9541).
+         (start-posn (event-start start-event))
+         (start-point (posn-point start-posn))
+         (start-window (posn-window start-posn))
+         (_ (with-current-buffer (window-buffer start-window)
+              (setq deactivate-mark nil)))
          ;; We've recorded what we needed from the current buffer and
          ;; window, now let's jump to the place of the event, where things
          ;; are happening.
          (_ (mouse-set-point start-event))
          (echo-keystrokes 0)
-         (start-posn (event-start start-event))
-         (start-point (posn-point start-posn))
-         (start-window (posn-window start-posn))
          (bounds (window-edges start-window))
          (make-cursor-line-fully-visible nil)
          (top (nth 1 bounds))