[gnome-shell-extensions] apps-menu: Only enable DND when there's a desktop

[Florian Müllner <fmuellner src gnome org>]

commit 09a60a27ba3c1dda954b6efe033326805d65f570
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Mar 15 05:23:57 2017 +0100

    apps-menu: Only enable DND when there's a desktop
    
    It's not very useful to allow dragging when there's no drop target,
    so tie the functionality added in the previous commit to the presence
    of a DESKTOP window.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=780371

 extensions/apps-menu/extension.js |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)
---
diff --git a/extensions/apps-menu/extension.js b/extensions/apps-menu/extension.js
index 404548d..5b01411 100644
--- a/extensions/apps-menu/extension.js
+++ b/extensions/apps-menu/extension.js
@@ -77,6 +77,13 @@ const ApplicationMenuItem = new Lang.Class({
         this.actor._delegate = this;
         let draggable = DND.makeDraggable(this.actor);
 
+        let maybeStartDrag = draggable._maybeStartDrag;
+        draggable._maybeStartDrag = (event) => {
+            if (this._dragEnabled)
+                return maybeStartDrag.call(draggable, event);
+            return false;
+        };
+
         draggable.connect('drag-begin', () => {
             Shell.util_set_hidden_from_pick(Main.legacyTray.actor, true);
         });
@@ -98,6 +105,10 @@ const ApplicationMenuItem = new Lang.Class({
         this.parent(active, params);
     },
 
+    setDragEnabled: function(enable) {
+        this._dragEnabled = enable;
+    },
+
     getDragActor: function() {
         return this._app.create_icon_texture(APPLICATION_ICON_SIZE);
     },
@@ -283,6 +294,10 @@ const DesktopTarget = new Lang.Class({
         });
     },
 
+    get hasDesktop() {
+        return this._desktop != null;
+    },
+
     _onWindowAdded: function(group, actor) {
         if (!(actor instanceof Meta.WindowActor))
             return;
@@ -300,6 +315,7 @@ const DesktopTarget = new Lang.Class({
         }
 
         this._desktop = desktop;
+        this.emit('desktop-changed');
 
         if (this._desktop) {
             this._desktopDestroyedId = this._desktop.connect('destroy', () => {
@@ -399,6 +415,11 @@ const ApplicationsButton = new Lang.Class({
         this._desktopTarget.connect('app-dropped', () => {
             this.menu.close();
         });
+        this._desktopTarget.connect('desktop-changed', () => {
+            this._applicationsButtons.forEach(item => {
+                item.setDragEnabled(this._desktopTarget.hasDesktop);
+            });
+        });
 
         this._applicationsButtons = new Map();
         this.reloadFlag = false;
@@ -673,6 +694,7 @@ const ApplicationsButton = new Lang.Class({
                let item = this._applicationsButtons.get(app);
                if (!item) {
                   item = new ApplicationMenuItem(this, app);
+                  item.setDragEnabled(this._desktopTarget.hasDesktop);
                   this._applicationsButtons.set(app, item);
                }
                if (!item.actor.get_parent())