From 3b54ab37edece2287495461afceff4d0960642a4 Mon Sep 17 00:00:00 2001
From: Sergey Biryukov <sergeybiryukov@git.wordpress.org>
Date: Wed, 20 Nov 2019 18:47:08 +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.

git-svn-id: https://develop.svn.wordpress.org/trunk@46754 602fd350-edb4-49c9-b593-d223f7449a82
---
 .../class-wp-customize-manager.php            | 20 +++++++++++++++++++
 tests/phpunit/tests/customize/manager.php     |  8 ++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/wp-includes/class-wp-customize-manager.php b/src/wp-includes/class-wp-customize-manager.php
index 17a6fa5767..decf0b87cf 100644
--- a/src/wp-includes/class-wp-customize-manager.php
+++ b/src/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/tests/phpunit/tests/customize/manager.php b/tests/phpunit/tests/customize/manager.php
index bca6decdc4..0adaade1b3 100644
--- a/tests/phpunit/tests/customize/manager.php
+++ b/tests/phpunit/tests/customize/manager.php
@@ -2829,6 +2829,14 @@ class Tests_WP_Customize_Manager extends WP_UnitTestCase {
 		$this->assertEquals( admin_url( 'edit.php' ), $this->manager->get_return_url() );
 	}
 
+	/**
+	 * @ticket 46686
+	 */
+	function test_return_url_with_deactivated_theme() {
+		$this->manager->set_return_url( admin_url( 'themes.php?page=mytheme_documentation' ) );
+		$this->assertEquals( admin_url( 'themes.php' ), $this->manager->get_return_url() );
+	}
+
 	/**
 	 * Test get_autofocus()/set_autofocus() methods.
 	 *