Add a term to list in block editor taxonomy sidebar

I’m the author of a plugin called Radio Buttons for taxonomies which converts certain taxonomy metaboxes (in classic) and sidebars (block editor) to use Radio buttons instead of checkboxes for selecting a term.

Unlike with checkboxes, which you can simply uncheck, with radio buttons if you want to offer someone the chance to “undo” a selection (or not apply a term) you need to provide an additional “term” they can select and then no save any value. It’s a sort of pseudo term if you will.

Due to this, I filter the result of get_terms() and add a fake term with a 0 value. On save, I check for a 0 value for the term and make sure there are no terms saved for that post.

To reduce it to something y’all can test, here’s an example code snippet:

/**
 * Add new 0 or null term in metabox and quickedit
 * this will allow users to "undo" a term if the taxonomy is not required
 *
 * @param array         $terms      Array of found terms.
 * @param array         $taxonomies An array of taxonomies.
 * @param array         $args       An array of get_terms() arguments.
 * @return array
 */
function kia_get_terms( $terms, $taxonomies, $args ) { 

    if ( isset( $args['fields'] ) && $args['fields'] == 'all' ) {

        $no_term = esc_html__( 'No term', 'my-text-domain' );

        $uncategorized = (object) array( 
            'term_id' => 0,
            'count' => 0,
            'description' => '',
            'name' => $no_term,
            'slug' => '0',
            'taxonomy' => 'category',
            'parent' => '0',
        );

        array_push( $terms, new WP_Term( $uncategorized ) );

    }

    return $terms;
}

add_filter( 'get_terms', 'kia_get_terms', 10, 3 );

In the classic editor, this works fine. But in the block editor (which still fetches the terms using get_terms() via the REST API… this causes an Uncaught (in promise) error and seems to get stuck in an infinite loop. How can I prevent this from looping?

Answers:

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Method 1

The problem is you are passing “term_id” as 0 in your code. Use -1 instead!. It will definitely show up in the Block Editor. I guess this is a bug of Gutenberg though.

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