Require tags for bbPress topics [closed]

In the back end, it’s a matter of using the hook save_post, as topic is a Custom Post Type.

If no Tags are filled, saving is cancelled and a link is presented so the user can go back to the editing screen.
But, there’s one caveat: the title is not preserved, if it is a new topic it comes back blank and if it is an existing topic any changes are lost. The content and topic attributes are preserved.
^{I’m not quite sure there is a solution for this…}

add_action( 'save_post', 'save_post_wpse_82956', 10, 2 );

/**
 * Require Tags for new bbPress Topic
 */
function save_post_wpse_82956( $post_id, $post_object ) 
{
    // Auto save or Ajax
    if ( 
        ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
        || ( defined('DOING_AJAX') && DOING_AJAX ) )
        return;

    // Correct post_type
    if ( 'topic' != $post_object->post_type )
        return;

    // First instance of the post (right after clicking "New Topic")
    if( 'auto-draft' == $post_object->post_status )
        return;

    if ( empty( $_POST['tax_input']['topic-tag'] ) ) 
        wp_die( '<a href="https://wordpress.stackexchange.com/questions/82956/javascript:history.go(-1)">' . __( '&laquo; &laquo; Please, add tags to the topic' ) . '</a>' );

}

---

And in the front end, a couple of bbPress action hooks and a simple check are enough (when posting multiple replies, a Javascript workaround is necessary, check comments):

add_action( 'bbp_new_topic_pre_extras', 'check_front_end_tags_wpse_82956' );
add_action( 'bbp_new_reply_pre_extras', 'check_front_end_tags_wpse_82956' );

function check_front_end_tags_wpse_82956()
{
    if( empty( $_POST['bbp_topic_tags'] ) )
    {
        // WORKAROUND FOR LINKS WITH HASH TAG, e.g., topic/lorem-ipsum#post-91
        // Necessary when posting multiple replies that generate hashed links
        // OTHERWISE A SIMPLE href="https://wordpress.stackexchange.com/questions/82956/javascript:history.go(-1) WOULD WORK
        ?><script>
        function goBack() {
            if (window.history && history.pushState) {
                history.replaceState("", "", "?no-tags=true);
                history.go(-1);
            }
        }
        </script><?php

        wp_die( '<a href="javascript:goBack()">' . __( '&laquo; &laquo; Please, add tags to the topic' ) . '</a>' );
    }
}