loading the `folding` mode with `use-package`

Question

I am using the folding minor mode in Emacs which I get installed with the following use-package macro:

(use-package folding
  :ensure t)

The above works and ensures that folding is installed whenever I fire up Emacs. However, when I visit a buffer with the folded marks ( // {{{ and // }}}), the minor mode is not automatically loaded and I have to load it explicitly with:

M-x folding-mode

I looked up the documentation and saw that for the Folding mode to start automatically when a folded file is loaded you need to do this:

(if (load "folding" 'nomessage 'noerror)
         (folding-mode-add-find-file-hook))

However, changing my use-package macro to the following:

(use-package folding
  :ensure t
  :config
  (if (load "folding" 'nomessage 'noerror)
      (folding-mode-add-find-file-hook))
  )

… makes no difference. I still have to load folding mode manually with M-x folding-mode. What gives?

update

Turns out that in addition to the accepted answer, I also had to add an Emacs file variable at the end of the file:

// {{{ folding-mode

// Local Variables:
// folded-file: t
// End:

// }}}

But adding this editor-specific markup in every source file is too much for me. Is there a way to automatically always activate folding-mode when visiting a buffer?

I have tried

(use-package folding
   :ensure t
   :config
     (folding-mode))

… and:

(use-package folding
   :ensure t
   :config
     (setq 'folding-mode t))

… but none of the above is working.

Answer 1

Just do

(use-package folding
  :ensure t
  :config
  (folding-mode-add-find-file-hook))

As to why, the

if (load "folding" 'nomessage 'noerror)

bit is really saying "try and load this package, and if it works invoke the next command" (see help for load). You take care of that using use-package already, so you just need to call the next command directly in :config.

Edit:

Based on the update, try something like this:

(use-package folding
  :ensure t
  :config
  (folding-install-hooks)
  (defun my-always-fold ()
    (setq-local folded-file t))
  (advice-add #'folding-mode-find-file :before #'my-always-fold))

That seems to work in my tests.

Answer 2

Try:

(use-package folding
  :ensure t
  :init
  (folding-mode-add-find-file-hook))

It seems that you want to only load folding-mode the first time you visit a folded file, but the hook that detects whether a file is folded is in the folding-mode package! This of course is impossible, you'll have to uncoditionally load folding-mode as above.

You may prefer to stick with:

(use-package folding
  :ensure t
  :config
  (folding-mode-add-find-file-hook))

It's not as bad you might think: it's true that on the very first folded file you open in a given session you'll have to manually run M-x folding-mode, but then the hook gets installed and any other folded file you open will get detected and put in folding-mode.