From 7ce128134985dd9fc3cb2a83dccf31d8b8924071 Mon Sep 17 00:00:00 2001
From: Felix Arntz <flixos90@git.wordpress.org>
Date: Mon, 4 Dec 2023 19:36:27 +0000
Subject: [PATCH] Themes: Avoid autoloading the previous theme's theme mods
 when switching to another theme.

This reduces unnecessarily autoloaded data from inactive themes, which can contribute to slow database performance as part of excessive autoloading.

Props mukesh27, rajinsharwar, igmoweb, joemcgill, swissspidy, westonruter, flixos90.
Fixes #59537.
See #59975.


git-svn-id: https://develop.svn.wordpress.org/trunk@57153 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/theme.php                     |  7 ++++
 .../phpunit/tests/theme/autoloadThemeMods.php | 42 +++++++++++++++++++
 2 files changed, 49 insertions(+)
 create mode 100644 tests/phpunit/tests/theme/autoloadThemeMods.php

diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index f063bc97a0..81c91ab5cc 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -840,6 +840,13 @@ function switch_theme( $stylesheet ) {
 	$new_theme->delete_pattern_cache();
 	$old_theme->delete_pattern_cache();
 
+	// Set autoload=no for the old theme, autoload=yes for the switched theme.
+	$theme_mods_options = array(
+		'theme_mods_' . $stylesheet                  => 'yes',
+		'theme_mods_' . $old_theme->get_stylesheet() => 'no',
+	);
+	wp_set_option_autoload_values( $theme_mods_options );
+
 	/**
 	 * Fires after the theme is switched.
 	 *
diff --git a/tests/phpunit/tests/theme/autoloadThemeMods.php b/tests/phpunit/tests/theme/autoloadThemeMods.php
new file mode 100644
index 0000000000..e653ac6a77
--- /dev/null
+++ b/tests/phpunit/tests/theme/autoloadThemeMods.php
@@ -0,0 +1,42 @@
+<?php
+
+require_once __DIR__ . '/base.php';
+
+/**
+ * Test autoload for theme mods.
+ *
+ * @package WordPress
+ * @subpackage Theme
+ *
+ * @group themes
+ */
+class Tests_Autoload_Theme_Mods extends WP_Theme_UnitTestCase {
+
+	/**
+	 * Tests that theme mods should not autoloaded after switch_theme.
+	 *
+	 * @ticket 39537
+	 */
+	public function test_that_on_switch_theme_previous_theme_mods_should_not_be_autoload() {
+		global $wpdb;
+
+		$current_theme_stylesheet = get_stylesheet();
+
+		// Set a theme mod for the current theme.
+		$new_theme_stylesheet = 'block-theme';
+		set_theme_mod( 'foo-bar-option', 'a-value' );
+
+		switch_theme( $new_theme_stylesheet );
+
+		$this->assertSame( 'no', $wpdb->get_var( $wpdb->prepare( "SELECT autoload FROM $wpdb->options WHERE option_name = %s", "theme_mods_$current_theme_stylesheet" ) ), 'Theme mods autoload value not set to no in database' );
+		$this->assertSame( 'yes', $wpdb->get_var( $wpdb->prepare( "SELECT autoload FROM $wpdb->options WHERE option_name = %s", "theme_mods_$new_theme_stylesheet" ) ), 'Theme mods autoload value not set to yes in database' );
+
+		switch_theme( $current_theme_stylesheet );
+
+		$this->assertSame( 'yes', $wpdb->get_var( $wpdb->prepare( "SELECT autoload FROM $wpdb->options WHERE option_name = %s", "theme_mods_$current_theme_stylesheet" ) ), 'Theme mods autoload value not set to yes in database' );
+		$this->assertSame( 'no', $wpdb->get_var( $wpdb->prepare( "SELECT autoload FROM $wpdb->options WHERE option_name = %s", "theme_mods_$new_theme_stylesheet" ) ), 'Theme mods autoload value not set to no in database' );
+
+		// Basic assertion to make sure that we haven't lost the mods.
+		$this->assertSame( 'a-value', get_theme_mod( 'foo-bar-option' ) );
+	}
+}