Hi Guix, this comes a little late, as Gnome folks have decided that evaluating arbitrary Javascript over DBus is perhaps not always the wisest idea¹, but I want to share with you a cool nifty tool regardless.
For starters, recall that Guix can only really set up its profile environment variables during login – that is if all processes are to respect them. This brings us into a weird chimera state after running `guix package': Any new variable introduced in our profile will be lost until we restart our shell. Or will it? Enter guile-ac-d-bus. With the newest version of Guile (3.0.9 at time of writing), we can actually connect to the session bus and do cool stuff with it. Watch me: --8<---------------cut here---------------start------------->8--- (define (d-bus-send/wait-for-reply bus message) (let ((serial (d-bus-write-message bus message))) (d-bus-conn-flush bus) (let loop ((msg (d-bus-read-message bus))) (if (equal? (d-bus-headers-ref (d-bus-message-headers msg) 'REPLY_SERIAL) serial) msg (loop (d-bus-read-message bus)))))) (let ((bus (d-bus-connect)) (message (make-d-bus-message MESSAGE_TYPE_METHOD_CALL 0 #f '() (vector (header-PATH "/org/freedesktop/DBus") (header-DESTINATION "org.freedesktop.DBus") (header-INTERFACE "org.freedesktop.DBus") (header-MEMBER "Hello")) #f))) (write (d-bus-send/wait-for-reply bus message)) (d-bus-disconnect bus)) --8<---------------cut here---------------end--------------->8--- Okay, but how does this solve our aforementioned problem? Well... --8<---------------cut here---------------start------------->8--- (define shell (make <service> #:docstring "Communicate with the GNOME Shell" #:provides '(gnome shell) #:start (lambda () (let ((bus (d-bus-connect)) (message (make-d-bus-message MESSAGE_TYPE_METHOD_CALL 0 #f '() (vector (header-PATH "/org/freedesktop/DBus") (header-DESTINATION "org.freedesktop.DBus") (header-INTERFACE "org.freedesktop.DBus") (header-MEMBER "Hello")) #f))) (d-bus-send/wait-for-reply bus message) bus)) #:stop (lambda (conn) (when conn (d-bus-disconnect conn)) #f) #:actions (let ((action->js (lambda (action . args) (format #f "imports.gi.GLib.~a(~{~s~^,~})" action args))) (shell-exec (lambda (conn js) (let ((method-call (make-d-bus-message MESSAGE_TYPE_METHOD_CALL 0 #f '() (vector (header-PATH "/org/gnome/Shell") (header-DESTINATION "org.gnome.Shell") (header-INTERFACE "org.gnome.Shell") (header-SIGNATURE "s") (header-MEMBER "Eval")) (list js)))) (let ((reply (d-bus-send/wait-for-reply conn method-call))) (apply peek 'reply (d-bus-message-body reply))))))) (make-actions (getenv (lambda (conn var) (and=> conn (cut shell-exec <> (action->js 'getenv var))))) (setenv (lambda (conn var val) (and=> conn (cut shell-exec <> (action->js 'setenv var val))))) (unsetenv (lambda (conn var) (and=> conn (cut shell-exec <> (action->js 'unsetenv var))))))))) --8<---------------cut here---------------end--------------->8--- Once you set the unsafe flag in Looking Glass and promise to be a very good girl, you can now extract environment variables. --8<---------------cut here---------------start------------->8--- $ herd getenv gnome PATH ;;; (reply #t "\"/gnu/store/s43dhx83c3a2g79vs5anf3wdmv9lwpi3-glib- 2.70.2-bin/bin:/run/setuid- programs:/home/yuri/.config/guix/current/bin:$HOME/.guix- profile/bin:$HOME/.guix-profile/sbin:/run/current- system/profile/bin:/run/current-system/profile/sbin\"") --8<---------------cut here---------------end--------------->8--- If you were naughty and didn't do the magic dance, you get a rather unhelpful result instead. --8<---------------cut here---------------start------------->8--- $ herd getenv gnome PATH ;;; (reply #f "") --8<---------------cut here---------------end--------------->8--- Anyway, we can now talk to DBus services from Shepherd, although doing so is currently a bit of a pain in the buttocks. Much of this is due to guile-ac-d-bus being somewhat obtuse and not having enough fibers in it. That being said, I'm sure there's some other use-case out there that is a good fit for this (wanna talk to loginctl for hibernation perhaps?) Cheers ¹ How dare they? Don't they know that this breaks my spacebar heating workflow?