3

If I have something like:

(use-package X
  :defer t
  (add-hook 'some-mode 'package-x-function))

Will that work as expected given that I set :defer t and the package doesn't have any "built-in" autoloads and I'm not using any of the autoload-creating use-package functions? In other words, does registering a hook alone take care of loading package X given that I set :defer t?

If not, what is the minimal additional configuration I require to make the hook work? Would I have to do something like :commands package-x-function?

5

I think this should do what you want:

(use-package X
  :commands package-x-function
  :init
  (add-hook 'some-mode 'package-x-function))

The :commands directive will generate an autoload for package-x-function, and the :init directive will immediately add it to the hook. Because :commands implies :defer, the package won't be loaded immediately. When the hook is run, the autoload will be looked up and the package will be loaded.

If you left off the :commands part, then you'd get a void-function error when the hook is run, because Emacs won't have a definition for package-x-function and there's no autoload to tell it how to get one.

  • Normally if the package wasn't deferred, you'd put the add-hook in the :config section, so that it wouldn't occur until the package was loaded. In this case thanks to the autoload created by :commands, it makes sense to put it in the :init right, otherwise there would never be a "trigger" run to autoload the package. – Jorge Israel Peña Jan 20 '16 at 19:54
  • Forgot to phrase my comment as a question. Would appreciate a confirmation on that. – Jorge Israel Peña Jan 20 '16 at 20:02
  • Correct. You need something to load the package, and so using the hook to do so means that it needs to be in :init rather than :config. – Aaron Harris Jan 20 '16 at 20:30

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