PR: https://github.com/mantisbt/mantisbt/pull/2226

It is important to note that the call plugin_file( ..., false, $this->basename ) is specified exactly this way, since this function may be called from another plugin; in that case, the current plugin will be the caller, not Mantis Graph.

Example of using Mantis Graph from other plugins:

/**
 * EVENT_CORE_HEADERS hook.
 */
public function core_headers() {
    ...
    if( plugin_is_loaded( 'MantisGraph' ) ) {
        if( gpc_get_string( 'page', '' ) === $this->basename . '/my_page_with_graphs.php' ) {
            $t_mantisgraph = plugin_get( 'MantisGraph' );
            $t_mantisgraph->include_chartjs();
        }
    }
}