Fatal error: call to undefined function wp_cache_get() (in option.php)

[dugwood]

Hello,

I've read a lot of issues about the missing wp_cache_get() function in some cases. And I think I've found some clues.

First, the website must be in Maintenance mode. I've seen a lot of reports on StackOverflow or the like with « upgrading », which is done after enabling the maintenance mode. When this happens, the wp-settings.php will stop early, avoiding the cache to be loaded.

But plugins, notably the translation plugins, are loaded. And many rely on cache to be present.

One way to deal with this, as we are in maintenance, so degraded status, is to load the default cache functions.

Using WordPress 6.7.1 it should be around line 383 in wp-includes/load.php:

<?php
        require_once ABSPATH . WPINC . '/functions.php';
        wp_load_translations_early();

Which may be changed as:

<?php
        require_once ABSPATH . WPINC . '/functions.php';
        require_once ABSPATH . WPINC . '/cache.php';
        wp_load_translations_early();

This way the translation plugins called in wp_load_translations_early() would work as expected.

[dugwood]

To build up on this: it's one of my patches that calls for get_locale() which in turn calls for get_option() which will call for wp_cache_get(). So maybe it's not related directly to plugins. But cache should be loaded anyway IMHO.

[abcd95]

Hey @dugwood, Welcome to Trac, and thanks for bringing this up.

Reproduction Report

Description

This report validates that the issue can be reproduced.

Environment

• WordPress: 6.7.1
• PHP: 8.2.25
• Server: nginx/1.27.2
• Database: mysqli (Server: 8.0.40 / Client: mysqlnd 8.2.25)
• Browser: Chrome 131.0.0.0
• OS: macOS
• Theme: Twenty Twenty-Five 1.0

Actual Results

A fatal occurs because wp_cache_get() is undefined, as cache.php is not loaded during maintenance mode.

Fatal error: Uncaught Error: Call to undefined function wp_cache_get() 

Additional Notes

This issue occurs specifically during WordPress maintenance mode (e.g., during upgrades)