package.el actually uses exactly the same method, it's just recompiling on startup makes the errors more noticable.
The function used is package--make-autoloads-and-compile
, which calls:
(byte-recompile-directory pkg-dir 0 t)
So the original code in the question is correct. However, to recompile a directory that isn't yet compiled, you can do the following:
(require 'dash)
(require 'f)
(defun was-compiled-p (path)
"Does the directory at PATH contain any .elc files?"
(--any-p (f-ext? it "elc") (f-files path)))
(defun ensure-packages-compiled ()
"If any packages installed with package.el aren't compiled yet, compile them."
(--each (f-directories package-user-dir)
(unless (was-compiled-p it)
(byte-recompile-directory it 0))))
(ensure-packages-compiled)