Show info for current stage in admin toolbar.

show-current-stage.php

<?php
/**
 * Show info for current stage in admin toolbar.
 */
function show_current_stage_info( $wp_admin_bar ) {
    if ( defined( 'WP_STAGE' ) && WP_STAGE != '%%WP_STAGE%%' ) {
        $args = array(
            'id'    => 'current-stage',
            'title' => '<span class="dashicons dashicons-admin-site" style="font-family: \'dashicons\'; font-size: 20px; margin-right: 5px;"></span> Current stage: ' . WP_STAGE,
            'meta'  => array( 'class' => 'current-stage' ),
            'parent' => 'top-secondary'
        );
        $wp_admin_bar->add_node( $args );
    }
}
add_action( 'admin_bar_menu', 'show_current_stage_info', 999 );