Fake Facet Ghost Choices

<?php

/** Add fake facet choices as ghosts - for example if you need to display terms that
 * don't have any posts in them yet, and you want them to appear as ghost choices.
 * This example is for basic non-hierarchal checkbox, but
 * could be adapted for Radio facets.
 * Note: allowing users to make non-existant selections can have 
 * weird side-effects.
  */
add_filter( 'facetwp_facet_html', function( $output, $params ) {

    if ( 'categories' == $params['facet']['name'] ) { // adjust name of facet

        /** Array of facet_value (the technical value of the choice), facetwp_display_value (the display value of the choice).
         * Could be added manually as below, or with some custom code 
         * to find the values that you need from terms or other sources.
         */
        $fake_facets = [ 'fake1' => 'Fake 1', 'fake2' => 'Another Fake' ];

        $fake_output = '';
        foreach ( $fake_facets as $fake => $fake_display ) {
            $fake_output .= '<div class="facetwp-checkbox disabled" data-value="' . $fake . '">' . $fake_display . ' <span class="facetwp-counter">(0)</span></div>';
        }

        $output = $output . $fake_output;

    }

    return $output;
}, 10, 2);