[gnome-shell] calendar: Use binding for clearButton visibility

[Florian Müllner <fmuellner src gnome org>]

commit 27da3ed1fec700cedd3735241c5160e85bbc5383
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Sat Aug 31 20:43:05 2019 +0200

    calendar: Use binding for clearButton visibility
    
    When the calendar PlaceHolder is visible, the ClearButton shouldn't
    be. Instead of setting the visibility explicitly, we can use a property
    binding.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/700

 js/ui/calendar.js | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/js/ui/calendar.js b/js/ui/calendar.js
index 2a4214e60f..4de3965acf 100644
--- a/js/ui/calendar.js
+++ b/js/ui/calendar.js
@@ -1,7 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported Calendar, CalendarMessageList */
 
-const { Clutter, Gio, GLib, Shell, St } = imports.gi;
+const { Clutter, Gio, GLib, GObject, Shell, St } = imports.gi;
 const Signals = imports.signals;
 
 const Main = imports.ui.main;
@@ -1075,6 +1075,10 @@ var CalendarMessageList = class CalendarMessageList {
         });
         box.add_actor(this._clearButton);
 
+        this._placeholder.actor.bind_property('visible',
+            this._clearButton, 'visible',
+            GObject.BindingFlags.INVERT_BOOLEAN);
+
         this._sectionList = new St.BoxLayout({ style_class: 'message-list-sections',
                                                vertical: true,
                                                y_expand: true,
@@ -1145,7 +1149,6 @@ var CalendarMessageList = class CalendarMessageList {
 
         let empty = sections.every(s => s.empty || !s.actor.visible);
         this._placeholder.actor.visible = empty;
-        this._clearButton.visible = !empty;
 
         let canClear = sections.some(s => s.canClear && s.actor.visible);
         this._clearButton.reactive = canClear;