add_filter( 'widget_tag_cloud_args','single_post_tag_cloud_tags' );
/**
* Output the tag_cloud only with tags of the single post as a list]
* @param array $args Display arguments.
* @return array Settings for the output.
*/
function single_post_tag_cloud_tags($args) {
global $post;
$post_tag_ids = wp_get_post_tags( $post->ID, array( 'fields' => 'ids' ) );
$args = array(
'include' => implode( ',',$post_tag_ids ),
'largest' => 12,
'smallest' => 12,
'format' => 'list',
);
return $args;
}

