Add unregister_taxonomy()

[swissspidy]

This is a follow-up to #11058.

While working on #14761 I stumbled upon the former ticket suggesting adding a unregister_taxonomy() function. It ended up with the addition of a new register_taxonomy_for_object_type() function.

Since _unregister_taxonomy() is used across all unit tests, I think we should add a real function for this for developers.

From Nacin's comment from three years ago:

An unregister_taxonomy() function needs to un-roll quite a bit:

• Remove the query var from the WP class, if one was registered.
• Remove any rewrite tags and permastructs.
• Remove the callback for handling the meta box.

An unregister_taxonomy() function should disallow the unregistration of 'post_tag' and 'category' until core does not assume they exist in many, many locations. The same block might also need to be in place in unregister_taxonomy_for_object_type() for the 'post' object type until core no longer breaks under any existing assumptions as well.

I'm gonna work on this together with #14761.

[swissspidy]

35227.diff​ adds the same remove_rewrite_tag() function as the patch in #14761 and does the following:

• Properly removes the taxonomy from the $wp_taxonomies global
• Removes rewrite tags and permastructs
• Removes the callback for handling the meta box
• Prevents unregistering built-in taxonomies

[swissspidy]

@boonebgorges You're the terms & taxonomy guy. Mind having a look at this one?

[boonebgorges]

@swissspidy A few thoughts, in no particular order:

• Docblock description for WP_Rewrite::remove_rewrite_tag() is copied from add_rewrite_tag() and needs to be updated.
• After unsetting array values in remove_rewrite_tag(), we could have gaps in the numerical array keys (ie: 0, 1, 3, 4). Does this matter? Worth resetting indexes using array_values() after unset()ing?
• Personal preference, but I'd say that with a new function (and no backward compatibility concerns) we should be returning descriptive WP_Error objects on various failures in unregister_taxonomy().
• Between this ticket and #14761, it's probably worth adding a WP::remove_query_arg() helper.
• Similarly, I'd prefer a remove_permastruct() method to reaching into $wp_rewrite's public properties.
• register_taxonomy() adds a specific callback to 'wp_ajax_add-' . $taxonomy, but when unregistering, you remove_all_actions(). Perhaps it's wiser to be conservative here and only undo the specific add_action() from register_taxonomy().
• In the test suite, don't remove _unregister_taxonomy(). Just make it a wrapper. Plugins are using it.

Looks like you have pretty well covered the various pieces of register_taxonomy() aside from these issues.

[swissspidy]

Replying to boonebgorges:

Thanks for your feedback so far! I incorporated it in the latest patch.

I created new tickets for adding the individual helper methods:

• #35234 for WP::remove_query_var()
• #35235 for remove_permastruct()
• #35236 for remove_rewrite_tag()

35227.2.diff​ relies on these patches, making this one much more readable.

After unsetting array values in remove_rewrite_tag(), we could have gaps in the numerical array keys (ie: 0, 1, 3, 4). Does this matter? Worth resetting indexes using array_values() after unset()ing?

I see no harm in not re-indexing the arrays.

[boonebgorges]

35227.2.diff​ is looking good - so much lovelier with the new functions :) Once those other tickets are landed, I think this one is good to go.

[swissspidy]

After the other tickets landed, I slightly updated the unit tests in 35227.3.diff​ to make them easier to read. Adds a new test_unregister_taxonomy_removes_permastruct() test.

[swissspidy]

In 36243:

Taxonomy: Introduce unregister_taxonomy().

This new function can be used to completely unregister non built-in taxonomies.

Fixes #35227.

[johnbillion]

In 36247:

Taxonomy: More tests for unregister_taxonomy().

See #35227

[DrewAPicture]

In 36961:

Docs: Improve the summary and return description in the DocBlock for unregister_taxonomy(), introduced in [36243].

See #35227. See #35986.