From 28e7acf1686ec4e31a4ced16c759560832eb7316 Mon Sep 17 00:00:00 2001
From: Sergey Biryukov <sergeybiryukov@git.wordpress.org>
Date: Mon, 1 Apr 2019 16:17:11 +0000
Subject: [PATCH] Customize: Only add `custom-background` to `body_class()` if
 the current theme supports custom background.

Props wido, swissspidy, ocean90, Mte90.
Fixes #38168.

git-svn-id: https://develop.svn.wordpress.org/trunk@45088 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/post-template.php         |  3 ++-
 src/wp-includes/theme.php                 |  4 ++-
 tests/phpunit/tests/post/getBodyClass.php | 32 +++++++++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/wp-includes/post-template.php b/src/wp-includes/post-template.php
index b817edec4f..3765e9873c 100644
--- a/src/wp-includes/post-template.php
+++ b/src/wp-includes/post-template.php
@@ -773,7 +773,8 @@ function get_body_class( $class = '' ) {
 		$classes[] = 'no-customize-support';
 	}
 
-	if ( get_background_color() !== get_theme_support( 'custom-background', 'default-color' ) || get_background_image() ) {
+	if ( current_theme_supports( 'custom-background' )
+		&& ( get_background_color() !== get_theme_support( 'custom-background', 'default-color' ) || get_background_image() ) ) {
 		$classes[] = 'custom-background';
 	}
 
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index 9a72126488..23907bc549 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -2730,7 +2730,9 @@ function _remove_theme_support( $feature ) {
 				break;
 			}
 			$support = get_theme_support( 'custom-background' );
-			remove_action( 'wp_head', $support[0]['wp-head-callback'] );
+			if ( isset( $support[0]['wp-head-callback'] ) ) {
+				remove_action( 'wp_head', $support[0]['wp-head-callback'] );
+			}
 			remove_action( 'admin_menu', array( $GLOBALS['custom_background'], 'init' ) );
 			unset( $GLOBALS['custom_background'] );
 			break;
diff --git a/tests/phpunit/tests/post/getBodyClass.php b/tests/phpunit/tests/post/getBodyClass.php
index 9c8ce670e6..c631199aa9 100644
--- a/tests/phpunit/tests/post/getBodyClass.php
+++ b/tests/phpunit/tests/post/getBodyClass.php
@@ -203,6 +203,38 @@ class Tests_Post_GetBodyClass extends WP_UnitTestCase {
 		$this->assertContains( 'attachment-jpeg', $class );
 	}
 
+	/**
+	 * @ticket 38168
+	 */
+	public function test_custom_background_class_is_added_when_theme_supports_it() {
+		add_theme_support( 'custom-background', array( 'default-color', '#ffffff' ) );
+		set_theme_mod( 'background_color', '#000000' );
+
+		$class = get_body_class();
+		$current_theme_supports_custom_background = current_theme_supports( 'custom-background' );
+
+		remove_theme_mod( 'background_color' );
+		remove_theme_support( 'custom-background' );
+
+		$this->assertTrue( $current_theme_supports_custom_background );
+		$this->assertContains( 'custom-background', $class );
+	}
+
+	/**
+	 * @ticket 38168
+	 */
+	public function test_custom_background_class_is_not_added_when_theme_support_is_missing() {
+		set_theme_mod( 'background_color', '#000000' );
+
+		$class = get_body_class();
+		$current_theme_supports_custom_background = current_theme_supports( 'custom-background' );
+
+		remove_theme_mod( 'background_color' );
+
+		$this->assertFalse( $current_theme_supports_custom_background );
+		$this->assertNotContains( 'custom-background', $class );
+	}
+
 	/**
 	 * @ticket 44005
 	 * @group privacy