Post ID facet

<?php

/**
 * Usage:
 *
 * 1. Add the following to your (child) theme's functions.php
 * 2. Create a new facet named "post_id"
 * 3. Set its data source to "Post Type" (this serves as a placeholder)
 * 4. Save and re-index
 */
add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'post_id' == $params['facet_name'] ) {
        $params['facet_value'] = $params['post_id'];
        $params['facet_display_value'] = $params['post_id'];
    }
    return $params;
}, 10, 2 );