register_taxonomy function does not check reserved taxonomies

[sebastiaandegeus]

the function register_taxonomy() in wp-includes/taxonomy.php does not check for reserved taxonomies. But later on this will cause malfunctions or unexpected behaviour and bugs.

I wrote a very simple patch that checks if any of the reserved taxonomies are being registered and if so it notifies the developer by _doing_it_wrong and WP_Error as a fallback.

Projects and plugins that are using reserved taxonomies in the wild will not break. But the developers will be notified via the logs or on their development environments where WP_DEBUG is true.

[danielbachhuber]

Projects and plugins that are using reserved taxonomies in the wild will not break.

But you're returning early and the taxonomy wouldn't be registered?

Co-Authors Plus uses an author taxonomy behind the scenes, which seems like a perfectly valid use that would be broken by this patch.

[danielbachhuber]

Related #31154

[SergeyBiryukov]

Duplicate of #12929 and #18263.