Update Services: use allowed_options in the Multisite snippet - #536

Fixes #535.

The Multisite snippet on Update Services adds ping_sites to the allowed options with the whitelist_options filter, which Core deprecated in WordPress 5.5. The page also offers the snippet as a custom plugin or must-use plugin, but the code block had no opening <?php tag or plugin header, so it did not work as a plugin file as written.

This:

• switches the filter to allowed_options and changes the "Whitelist" comment to "Allow";
• adds <?php and a Plugin Name header, so the block works as a must-use plugin or as a regular plugin;
• adds a note that the snippet uses the allowed_options filter added in WordPress 5.5, and that older versions should use whitelist_options instead.

Testing

In Docker, on a Multisite network (subdirectory install) with WP_DEBUG and WP_DEBUG_LOG on, the network admin saved Settings > Writing with a new Update Services URL. The tested file is the page's code block, byte for byte.

WordPress 7.1.3 (PHP 8.3):

• No snippet: the Update Services field is not shown, and saving leaves ping_sites unchanged.
• Old snippet (whitelist_options), must-use plugin: the URL is saved, and debug.log gets "Hook whitelist_options is deprecated since version 5.5.0! Use allowed_options instead."
• New snippet, must-use plugin: the URL is saved, with no deprecation notice.
• New snippet, regular plugin: listed as "Update Services for Multisite", network activated, the URL is saved, with no deprecation notice.

WordPress 5.4.2 (PHP 7.4):

• Old snippet: the URL is saved, with no notice (the filter was not deprecated yet).
• New snippet: the field is shown, but the URL is not saved, which is the case the new version note covers.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code and Codex
Used for: Finding the issue by checking the handbook's hook names against Core, the change, Docker testing, and the wording of this description. I reviewed the change and the results, and I take responsibility for the contribution.