From fa2ddcc52f5dc5bda1336abcbaed1bf30234a465 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20=C3=85dahl?= <jadahl@gmail.com>
Date: Thu, 3 Jan 2019 11:53:13 +0100
Subject: [PATCH] dnd: Repick target actor if destroyed mid iteration

The picked target actor may be destroyed (e.g. hover style change
resulting in the ClutterTexture to be destroyed). If we don't handle
this, GJS will abort when it sees the exception caused by Javascript
code trying to access the destroyed target actor.

To handle it, listen on the 'destroy' signal on the target actor, and
repick, so a valid actor is passed to the next motion callback.

Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/632

(cherry picked from commit 4259676f6e09de275d29dcae5b00026f26faa9ab)
---
 js/ui/dnd.js | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index a38607c24..ec1ba1d41 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -396,10 +396,15 @@ var _Draggable = new Lang.Class({
         return true;
     },
 
+    _pickTargetActor() {
+        return this._dragActor.get_stage().get_actor_at_pos(Clutter.PickMode.ALL,
+                                                            this._dragX, this._dragY);
+    },
+
     _updateDragHover() {
         this._updateHoverId = 0;
-        let target = this._dragActor.get_stage().get_actor_at_pos(Clutter.PickMode.ALL,
-                                                                  this._dragX, this._dragY);
+        let target = this._pickTargetActor();
+
         let dragEvent = {
             x: this._dragX,
             y: this._dragY,
@@ -407,6 +412,18 @@ var _Draggable = new Lang.Class({
             source: this.actor._delegate,
             targetActor: target
         };
+
+        let targetActorDestroyHandlerId;
+        let handleTargetActorDestroyClosure;
+        handleTargetActorDestroyClosure = () => {
+            target = this._pickTargetActor();
+            dragEvent.targetActor = target;
+            targetActorDestroyHandlerId =
+                target.connect('destroy', handleTargetActorDestroyClosure);
+        };
+        targetActorDestroyHandlerId =
+            target.connect('destroy', handleTargetActorDestroyClosure);
+
         for (let i = 0; i < dragMonitors.length; i++) {
             let motionFunc = dragMonitors[i].dragMotion;
             if (motionFunc) {
@@ -417,6 +434,7 @@ var _Draggable = new Lang.Class({
                 }
             }
         }
+        dragEvent.targetActor.disconnect(targetActorDestroyHandlerId);
 
         while (target) {
             if (target._delegate && target._delegate.handleDragOver) {