use-package: How to defer loading a command when depending on other deferred packages?

Question

I would like to autoload the command f-join from f.el using use-package. Note that the package f.el depends on the packages dash.el and s.el. Here is a minimal example:

(setq debug-on-error t)
(let ((default-directory  "~/test/emacs")
      (packages (list "dash.el" "f.el" "s.el" "use-package")))
  (dolist (package packages)
    (add-to-list 'load-path (expand-file-name package))))

(eval-when-compile
  (require 'use-package))

(use-package dash
  :defer t)

(use-package f
  :after (s dash)   ;; make loading order-independent
  :commands f-join  ;; add autoload for f-join
  :defer t)

(use-package s
  :defer t)

(f-join "a" "b")
(message-box "Everything ok")

Running this with emacs -Q -l gives error:

Debugger entered--Lisp error: (void-function f-join)

Changing :defer to :demand on the dependent packages dash.el and s.el eliminates the error message, but now the packages are no longer autoloaded, which is what I wanted to avoid.

Answer 1

Remove :after (s dash), they will be required while loading f.el.

By using M-x emacs-lisp-macroexpand, you can expand your use-package use into

(progn
  (defvar use-package--warning281
    #'(lambda
        (keyword err)
        (let
            ((msg
              (format "%s/%s: %s" 'f keyword
                      (error-message-string err))))
          (display-warning 'use-package msg :error))))
  (condition-case-unless-debug err
      (eval-after-load 'dash
        '(eval-after-load 's
           '(unless
                (fboundp 'f-join)
              (autoload #'f-join "f" nil t))))
    (error
     (funcall use-package--warning281 :catch err))))

So f-join is not autoloaded in time.