[gnome-shell] boxpointer: If available, use source actor for constraining

[Jonas Ådahl <jadahl src gnome org>]

commit 96e14dcbe76cb2b7fc2dcb972a97575a7cb4a724
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Sep 4 14:37:45 2017 +0800

    boxpointer: If available, use source actor for constraining
    
    If a source actor is set, use that for determining the arrow side (i.e.
    whether the BoxPointer widget should expand in a certain direction).
    This is better because it ensures that the popup is displayed on the
    same monitor as the widget it originates from.
    
    Without this, entering text with a vertically aligned input method
    close to the bottom of a monitor would expand the BoxPointer downwards
    on the monitor beneath it, instead of upwards, which is what one would
    expect.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786886

 js/ui/boxpointer.js |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/boxpointer.js b/js/ui/boxpointer.js
index 091ae15..4527b4d 100644
--- a/js/ui/boxpointer.js
+++ b/js/ui/boxpointer.js
@@ -587,7 +587,10 @@ var BoxPointer = new Lang.Class({
     _calculateArrowSide: function(arrowSide) {
         let sourceAllocation = Shell.util_get_transformed_allocation(this._sourceActor);
         let [minWidth, minHeight, boxWidth, boxHeight] = this._container.get_preferred_size();
-        let monitor = Main.layoutManager.findMonitorForActor(this.actor);
+        let monitorActor = this.sourceActor;
+        if (!monitorActor)
+            monitorActor = this.actor;
+        let monitor = Main.layoutManager.findMonitorForActor(monitorActor);
 
         switch (arrowSide) {
         case St.Side.TOP: