WordPress Remove CPT Base URL and Ensure Unique Slug

removecptslug.php

<?php
/**
 * Add in functions.php or in a specialized plugin
 * Change 'location' to the desired CPT which should already exist
 * (example created via ACF)
 * Mostly extracted from https://wordpress.stackexchange.com/questions/203951/remove-slug-from-custom-post-type-post-urls
 * By Matt Keys, arafatgazi and others
 */
// remove post type from permalinks
function remove_post_type( $post_link, $post, $leavename ) {

    if ( $post->post_type != 'location' ) {
        return $post_link;
    } else {
        $post_link = str_replace( '/' . $post->post_type . '/', '/', $post_link );
        return $post_link;
    }
}
add_filter( 'post_type_link', 'remove_post_type', 10, 3 );


// instruct wordpress on how to find posts from the new permalinks
function parse_request_remove_cpt_slug( $query_vars ) {

    // return if admin dashboard 
    if ( is_admin() ) {
        return $query_vars;
    }

    // return if pretty permalink isn't enabled
    if ( ! get_option( 'permalink_structure' ) ) {
        return $query_vars;
    }

    $cpt = 'location';

    // store post slug value to a variable
    if ( isset( $query_vars['pagename'] ) ) {
        $slug = $query_vars['pagename'];
    } elseif ( isset( $query_vars['name'] ) ) {
        $slug = $query_vars['name'];
    } else {
        global $wp;
        
        $path = $wp->request;

        // use url path as slug
        if ( $path && strpos( $path, '/' ) === false ) {
            $slug = $path;
        } else {
            $slug = false;
        }
    }

    if ( $slug ) {
        $post_match = get_page_by_path( $slug, 'OBJECT', $cpt );

        if ( ! is_admin() && $post_match ) {

            // remove any 404 not found error element from the query_vars array because a post match already exists in cpt
            if ( isset( $query_vars['error'] ) && $query_vars['error'] == 404 ) {
                unset( $query_vars['error'] );
            }

            // remove unnecessary elements from the original query_vars array
            unset( $query_vars['pagename'] );
    
            // add necessary elements in the the query_vars array
            $query_vars['post_type'] = $cpt;
            $query_vars['name'] = $slug;
            $query_vars[$cpt] = $slug; // this constructs the "cpt=>post_slug" element
        }
    }

    return $query_vars;
}
add_filter( 'request', "parse_request_remove_cpt_slug" , 1, 1 );

// avoid creating posts, pages or CPT (ie location) with existing slugs.
function prevent_slug_duplicates( $slug, $post_ID, $post_status, $post_type, $post_parent, $original_slug ) {
    $check_post_types = array(
        'post',
        'page',
        'location'
    );
    
    // If not one of the types we care about, just return the slug
    if ( ! in_array( $post_type, $check_post_types ) ) {
        return $slug;
    }

    // Check for duplicate slug in relevant post types
    $suffix = 1;
    $original_slug = $slug;
    
    // Loop until we find a unique slug
    while ( true ) {
        if ( 'location' == $post_type ) {
            // Check for existing post or page with the same slug
            $post_match = get_page_by_path( $slug, 'OBJECT', 'post' );
            $page_match = get_page_by_path( $slug, 'OBJECT', 'page' );

            if ( $post_match || $page_match ) {
                $slug = $original_slug . '-' . $suffix;
                $suffix++;
            } else {
                break; // Slug is unique, exit loop
            }
        } else {
            // Check if location already exists with the same slug for a post or page
            $custom_post_type_match = get_page_by_path( $slug, 'OBJECT', 'location' );

            if ( $custom_post_type_match ) {
                $slug = $original_slug . '-' . $suffix;
                $suffix++;
            } else {
                break; // Slug is unique, exit loop
            }
        }
    }

    return $slug;
}
add_filter( 'wp_unique_post_slug', 'prevent_slug_duplicates', 10, 6 );