[gnome-shell/wip/fix-panel-destroy-handler-leak] panel: Disconnect destroy signal handler when needed

[Ray Strode <halfline src gnome org>]

commit dfbbf07511b827d9d9c2f5f4e6289f28892ae643
Author: Ray Strode <rstrode redhat com>
Date:   Tue Oct 6 10:29:00 2020 -0400

    panel: Disconnect destroy signal handler when needed
    
    The panel corners try to match their style to the buttons closest
    to them. In order to make sure the corner styles stay in sync with
    their neighboring buttons, they connect to the style-changed signals
    of the buttons.
    
    In order to make sure the style-changed signal handler isn't leaked,
    it gets disconnected when the button is destroyed.
    
    Unfortunately, the destroy signal handler connection itself gets leaked!
    
    This commit ensures the destroy signal handler gets disconnected any
    time the neighboring button is re-determined.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1460

 js/ui/panel.js | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)
---
diff --git a/js/ui/panel.js b/js/ui/panel.js
index b168907def..4f664e2499 100644
--- a/js/ui/panel.js
+++ b/js/ui/panel.js
@@ -591,14 +591,20 @@ class PanelCorner extends St.DrawingArea {
             button = this._findRightmostButton(box);
 
         if (button) {
-            if (this._button && this._buttonStyleChangedSignalId) {
-                this._button.disconnect(this._buttonStyleChangedSignalId);
-                this._button.style = null;
+            if (this._button) {
+                if (this._buttonStyleChangedSignalId) {
+                    this._button.disconnect(this._buttonStyleChangedSignalId);
+                    this._button.style = null;
+                }
+
+                if (this._buttonDestroySignalId) {
+                    this._button.disconnect(this._buttonDestroySignalId);
+                }
             }
 
             this._button = button;
 
-            button.connect('destroy', () => {
+            this._buttonDestroySignalId = button.connect('destroy', () => {
                 if (this._button == button) {
                     this._button = null;
                     this._buttonStyleChangedSignalId = 0;