How to conditionally use :straight?

[jthaman]

I have a computer that uses guix to manage emacs packages, but on my other computers, I would like to use straight to manage them. I'm trying to figure out how to make minimal changes to my init.el so that that I can use the same init on all machines.

Something like this fails:

(defvar guix-p (string-match-p "guix" (shell-command-to-string "cat /proc/version")))

(use-package no-littering
  :demand t
  :straight (not guix-p)  ; interprets not as a package
  :config
  (no-littering-theme-backups))

What's the right way to change the use-package macro so that the straight keyword is conditionally used on non-guix systems?

[raxod502]

There's no direct way to do this with use-package. You can instead just separate out the straight.el invocation, to:

(if guix-p
    (straight-register-package 'no-littering)
  (straight-use-package 'no-littering))
  
(use-package no-littering
  :demand t
  :config
  (no-littering-theme-backups))

If you want, you could write a macro wrapping use-package that would implement this behavior by default, and use it in your configuration.

[jthaman]

Many thanks for the explanation