Reformatter elixir configuration

reformatter-elixir.el

(use-package reformatter
  :ensure t
  :config
  ; Adds a reformatter configuration called "+elixir-format"
  ; This uses "mix format -"
  (reformatter-define +elixir-format
    :program "mix"
    :args '("format" "-"))
  ; defines a function that looks for the .formatter.exs file used by mix format
  (defun +set-default-directory-to-mix-project-root (original-fun &rest args)
    (if-let* ((mix-project-root (and buffer-file-name
                                     (locate-dominating-file buffer-file-name
                                                             ".formatter.exs"))))
        (let ((default-directory mix-project-root))
          (apply original-fun args))
      (apply original-fun args)))
  ; adds an advice to the generated function +elxir-format-region that sets the proper root dir
  ; mix format needs to be run from the root directory otherwise it wont use the formatter configuration
  (advice-add '+elixir-format-region :around #'+set-default-directory-to-mix-project-root)
  ; Adds a hook to the major-mode that will add the generated function +elixir-format-on-save-mode
  ; So, every time we save an elixir file it will try to find a .formatter.exs and then run mix format from
  ; that file's directory
  (add-hook 'elixir-mode-hook #'+elixir-format-on-save-mode))