Add duplicate link to admin bar menu

add_action( 'admin_bar_menu', function ( $admin_bar ) {

	// Only show this when editing a post.

	$screen = get_current_screen();

	if ( ! $screen || 'post' !== $screen->base ) {

		return;

	}

	$post             = get_post();

	$post_type_object = get_post_type_object( $post->post_type );

	if ( null === $post_type_object || ! current_user_can( $post_type_object->cap->create_posts ) ) {

		return;

	}

	$url = wp_nonce_url(

		add_query_arg(

			array(

				'action'  => 'wpcode_snippet_duplicate_post',

				'post_id' => $post->ID,

			),

			'admin.php'

		),

		'wpcode_duplicate_post_' . $post->ID,

		'wpcode_duplicate_nonce'

	);

	$admin_bar->add_menu(

		array(

			'id'    => 'wpcode_duplicate',

			'title' => 'Duplicate',

			'href'  => $url,

		)

	);

}, 1100 );