Aggiunge all'indice di ricerca di wp anche i campi acf (da verificare come funzioni esattamente) From https://support.advancedcustomfields.com/forums/topic/making-acf-data-available-to-wp_search/

acf-extend-search.php

<?php
// Make the search to index custom
/**
 * Extend WordPress search to include custom fields
 * http://adambalee.com
 *
 * Join posts and postmeta tables
 * http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_join
 */
function cf_search_join( $join ) {
    global $wpdb;
    if ( is_search() ) {    
        $join .=' LEFT JOIN '.$wpdb->postmeta. ' ON '. $wpdb->posts . '.ID = ' . $wpdb->postmeta . '.post_id ';
    }
    return $join;
}
add_filter('posts_join', 'cf_search_join' );

/**
 * Modify the search query with posts_where
 * http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_where
 */
function cf_search_where( $where ) {
    global $pagenow, $wpdb;
    if ( is_search() ) {
        $where = preg_replace(
            "/\(\s*".$wpdb->posts.".post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
            "(".$wpdb->posts.".post_title LIKE $1) OR (".$wpdb->postmeta.".meta_value LIKE $1)", $where );
    }
    return $where;
}
add_filter( 'posts_where', 'cf_search_where' );

/**
 * Prevent duplicates
 * http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_distinct
 */
function cf_search_distinct( $where ) {
    global $wpdb;
    if ( is_search() ) {
        return "DISTINCT";
    }
    return $where;
}
add_filter( 'posts_distinct', 'cf_search_distinct' );