From d5434d7cc72591d4f9e8afcd646c0fcf136249ba Mon Sep 17 00:00:00 2001
From: Sergey Biryukov <sergeybiryukov.ru@gmail.com>
Date: Wed, 20 Nov 2019 18:49:03 +0000
Subject: [PATCH] Customize: If the return URL for Close button is a page added
 to the Appearance menu by a deactivated theme, fall back to the Themes
 screen.

Props JarretC, Jean-David, SergeyBiryukov.
Fixes #46686.
Built from https://develop.svn.wordpress.org/trunk@46754


git-svn-id: http://core.svn.wordpress.org/trunk@46554 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/class-wp-customize-manager.php | 20 ++++++++++++++++++++
 wp-includes/version.php                    |  2 +-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index 17a6fa5767..decf0b87cf 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -4622,9 +4622,13 @@ final class WP_Customize_Manager {
 	 *
 	 * @since 4.4.0
 	 *
+	 * @global array $_registered_pages
+	 *
 	 * @return string URL for link to close Customizer.
 	 */
 	public function get_return_url() {
+		global $_registered_pages;
+
 		$referer                    = wp_get_referer();
 		$excluded_referer_basenames = array( 'customize.php', 'wp-login.php' );
 
@@ -4637,6 +4641,22 @@ final class WP_Customize_Manager {
 		} else {
 			$return_url = home_url( '/' );
 		}
+
+		$return_url_basename = wp_basename( parse_url( $this->return_url, PHP_URL_PATH ) );
+		$return_url_query    = parse_url( $this->return_url, PHP_URL_QUERY );
+
+		if ( 'themes.php' === $return_url_basename && $return_url_query ) {
+			parse_str( $return_url_query, $query_vars );
+
+			/*
+			 * If the return URL is a page added by a theme to the Appearance menu via add_submenu_page(),
+			 * verify that belongs to the active theme, otherwise fall back to the Themes screen.
+			 */
+			if ( isset( $query_vars['page'] ) && ! isset( $_registered_pages[ "appearance_page_{$query_vars['page']}" ] ) ) {
+				$return_url = admin_url( 'themes.php' );
+			}
+		}
+
 		return $return_url;
 	}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 1e7face89a..1bbc25bcfe 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.4-alpha-46753';
+$wp_version = '5.4-alpha-46754';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.