Customize: Fix regression in ability to create submenus for nav menus via drag and drop.

See #34391.
Fixes #38948 for 4.7 branch.
Props delawski, adamsilverstein.

Built from https://develop.svn.wordpress.org/branches/4.7@39377


git-svn-id: http://core.svn.wordpress.org/branches/4.7@39317 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/customize-nav-menus.js

@@ -1029,7 +1029,7 @@
 		},
 
 		onChangeExpanded: function( expanded, args ) {
-			var section = this;
+			var section = this, completeCallback;
 
 			if ( expanded ) {
 				wpNavMenu.menuList = section.contentContainer;
@@ -1045,6 +1045,11 @@
 					}
 				} );
 
+				// Make sure Sortables is initialized after the section has been expanded to prevent `offset` issues.
+				if ( args.completeCallback ) {
+					completeCallback = args.completeCallback;
+				}
+				args.completeCallback = function() {
 					if ( 'resolved' !== section.deferred.initSortables.state() ) {
 						wpNavMenu.initSortables(); // Depends on menu-to-edit ID being set above.
 						section.deferred.initSortables.resolve( wpNavMenu.menuList ); // Now MenuControl can extend the sortable.
@@ -1052,6 +1057,10 @@
 						// @todo Note that wp.customize.reflowPaneContents() is debounced, so this immediate change will show a slight flicker while priorities get updated.
 						api.control( 'nav_menu[' + String( section.params.menu_id ) + ']' ).reflowMenuItems();
 					}
+					if ( _.isFunction( completeCallback ) ) {
+						completeCallback();
+					}
+				};
 			}
 			api.Section.prototype.onChangeExpanded.call( section, expanded, args );
 		}

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-RC1-39374';
+$wp_version = '4.7-RC1-39377';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.