allView: Remove icon from folder when dropping outside

When dropping an app icon to outside the folder, remove the
app from that folder. GNOME Shell is already smart enough
to figure out the setting changes and update the icons.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/603

js/ui/appDisplay.js

@@ -731,6 +731,38 @@ var AllView = class AllView extends BaseAppView {
         }
     }
 
+    _canDropAt(source) {
+        if (!(source instanceof AppIcon))
+            return false;
+
+        if (!global.settings.is_writable('favorite-apps'))
+            return false;
+
+        if (!(source.view instanceof FolderView))
+            return false;
+
+        return true;
+    }
+
+    handleDragOver(source, actor, x, y, time) {
+        if (!this._canDropAt(source))
+            return DND.DragMotionResult.NO_DROP;
+
+        return DND.DragMotionResult.MOVE_DROP;
+    }
+
+    acceptDrop(source, actor, x, y, time) {
+        if (!this._canDropAt(source))
+            return false;
+
+        source.view.removeApp(source.app);
+
+        if (this._currentPopup)
+            this._currentPopup.popdown();
+
+        return true;
+    }
+
     inhibitEventBlocker() {
         this._nEventBlockerInhibits++;
         this._eventBlocker.visible = this._nEventBlockerInhibits == 0;
@@ -1248,6 +1280,19 @@ var FolderView = class FolderView extends BaseAppView {
 
         return apps;
     }
+
+    removeApp(app) {
+        let folderApps = this._folder.get_strv('apps');
+        let index = folderApps.indexOf(app.id);
+        if (index < 0)
+            return false;
+
+        folderApps.splice(index, 1);
+
+        this._folder.set_strv('apps', folderApps);
+
+        return true;
+    }
 };
 
 var FolderIcon = class FolderIcon {