(use-modules (srfi srfi-9)
             (srfi srfi-9 gnu)
             (guix utils)
             (gnu)
             (gnu services)
             (gnu services shepherd))

(define add-service-requirement (lambda (service-type requirement)
    (set-field service-type (service-type-extensions)
            (map
                (lambda (ext)
                    (if (eq? (service-extension-target ext) shepherd-root-service-type)
                        (set-field ext (service-extension-compute)
                            (let ((comp (service-extension-compute ext)))
                                (lambda (. args)
                                  (let ((serv (apply comp args)))
                                    (map (lambda (serv)
                                          (set-field serv (shepherd-service-requirement) (append requirement (shepherd-service-requirement serv))))
                                         serv)))))
                        ext))
                (service-type-extensions service-type)))))