From a77b7447d73398a4d2b05489b09f51c37b0f41ac 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
---
 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 431c60d6c..9e961a186 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -411,10 +411,15 @@ 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,
@@ -422,6 +427,18 @@ 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) {
@@ -432,6 +449,7 @@ var _Draggable = new Lang.Class({
                 }
             }
         }
+        dragEvent.targetActor.disconnect(targetActorDestroyHandlerId);
 
         while (target) {
             if (target._delegate && target._delegate.handleDragOver) {