Fix live previews for moving widget to another sidebar

* Send all sidebars_widgets settings, not just the setting for the widget being edited
* Let incoming customized POST data completely override sidebars_widgets settings; stop merging
* Stop deleting widget instance settings from preview customizer because unnecessary and
  because of possible race condition when moving widgets across sidebars

widget-customizer-preview.js

@@ -179,14 +179,18 @@ var WidgetCustomizerPreview = (function ($) {
 							return;
 						}
 
+						var customized = {};
 						var sidebar_id = null;
-						var sidebar_widgets = [];
 						wp.customize.each( function ( setting, setting_id ) {
 							var matches = setting_id.match( /^sidebars_widgets\[(.+)\]/ );
-							if ( matches && setting().indexOf( widget_id ) !== -1 ) {
-								sidebar_id = matches[1];
-								sidebar_widgets = setting();
+							if ( ! matches ) {
+								return;
+							}
+							var other_sidebar_id = matches[1];
+							if ( setting().indexOf( widget_id ) !== -1 ) {
+								sidebar_id = other_sidebar_id;
 							}
+							customized[sidebar_id_to_setting_id( other_sidebar_id )] = setting();
 						} );
 						if ( ! sidebar_id ) {
 							throw new Error( 'Widget does not exist in a sidebar.' );
@@ -199,8 +203,7 @@ var WidgetCustomizerPreview = (function ($) {
 							setting_id: setting_id,
 							setting: JSON.stringify( to )
 						};
-						var customized = {};
-						customized[ sidebar_id_to_setting_id( sidebar_id ) ] = sidebar_widgets;
+
 						customized[setting_id] = to;
 						data.customized = JSON.stringify(customized);
 						data[self.render_widget_nonce_post_key] = self.render_widget_nonce_value;
@@ -286,16 +289,9 @@ var WidgetCustomizerPreview = (function ($) {
 							return;
 						}
 
-						// Remove widgets (their DOM element and their setting) when removed from sidebar
+						// Delete the widget from the DOM if it no longer exists in the sidebar
 						$.each( from, function ( i, old_widget_id ) {
 							if ( -1 === to.indexOf( old_widget_id ) ) {
-								var setting_id = widget_id_to_setting_id( old_widget_id );
-								if ( wp.customize.has( setting_id ) ) {
-									wp.customize.remove( setting_id );
-									delete already_bound_widgets[setting_id];
-								}
-
-								// Delete the widget from the DOM if it wasn't added to its new location in the other sidebar
 								self.getSidebarWidgetElement( sidebar_id, old_widget_id ).remove();
 							}
 						} );

widget-customizer.js

@@ -168,13 +168,12 @@ var WidgetCustomizer = (function ($) {
 					return widget_form_controls.container[0];
 				} );
 
-				// Re-sort widget form controls
+				// Re-sort widget form controls (including widgets form other sidebars newly moved here)
 				sidebar_widgets_add_control.before( final_control_containers );
 				control.applyCardinalOrderClassNames();
 
 				// If the widget was dragged into the sidebar, make sure the sidebar_id param is updated
 				_( widget_form_controls ).each( function ( widget_form_control ) {
-					// @todo We need to delete the widget from the old sidebar, and re-fetch via Ajax
 					widget_form_control.params.sidebar_id = control.params.sidebar_id;
 				} );
 

widget-customizer.php

@@ -269,10 +269,7 @@ static function prepreview_added_sidebars_widgets( $sidebars_widgets ) {
 		foreach ( self::$_customized as $setting_id => $value ) {
 			if ( preg_match( '/^sidebars_widgets\[(.+?)\]$/', $setting_id, $matches ) ) {
 				$sidebar_id = $matches[1];
-				if ( ! isset( $sidebars_widgets[$sidebar_id] ) ) {
-					$sidebars_widgets[$sidebar_id] = array();
-				}
-				$sidebars_widgets[$sidebar_id] = array_unique( array_merge( $value, $sidebars_widgets[$sidebar_id] ) );
+				$sidebars_widgets[$sidebar_id] = $value;
 			}
 		}
 		return $sidebars_widgets;