Emacs Tree View

by Mads Hartmann - 12 May 2016

Every once in a while I find it really convenient to use a tree-like project explorer to get an overview of the project I'm working on. For me this is especially the case when working on new projects or during pair-prgramming sessions. This feature has become ubiquitous in all editors and Emacs does have quit a lot of packages that try to solve this problem. Throughout the years I've tried a couple of them (some examples being sr-speedbar, project-explorer, emacs-neotree) but none of them really seem to cut it for me so I sat down and did a bit of elisp.

Here are a couple of the features I was looking for

I believe I've accomplished this without too much hacking around; I'm using a couple of packages and some built-in emacs features.

Lets start with the packages. I'm using use-package to configure all my emacs packages; if you aren't using it already I can really recommend it.

The first part of the solution is dired-subtree. This is a very helpful package that makes it possible to insert a subdirectory as a separate listing in the active dired buffer thus giving you a tree-like dired buffer.

(use-package dired-subtree
  (:map dired-mode-map
	("<enter>" . mhj/dwim-toggle-or-open)
	("<return>" . mhj/dwim-toggle-or-open)
	("<tab>" . mhj/dwim-toggle-or-open)
	("<down-mouse-1>" . mhj/mouse-dwim-to-toggle-or-open))
    ;; Function to customize the line prefixes (I simply indent the lines a bit)
    (setq dired-subtree-line-prefix (lambda (depth) (make-string (* 2 depth) ?\s)))
    (setq dired-subtree-use-backgrounds nil)))

The functions mhj/dwim-toggle-or-open and mhj/mouse-dwim-to-toggle-or-open are optional but I use them to either expand a folder or open a file depending on the what is under the point when you execute it. Here's the implementation.

(defun mhj/dwim-toggle-or-open ()
  "Toggle subtree or open the file."
  (if (file-directory-p (dired-get-file-for-visit))

(defun mhj/mouse-dwim-to-toggle-or-open (event)
  "Toggle subtree or the open file on mouse-click in dired."
  (interactive "e")
  (let* ((window (posn-window (event-end event)))
	 (buffer (window-buffer window))
	 (pos (posn-point (event-end event))))
      (with-current-buffer buffer
	(goto-char pos)

So now we have a dired buffer that works as a tree-view. To have dired put folders before files in its list, and to hide a couple of files I don't care about I use the following configuration

(use-package dired
  :ensure nil
    (setq insert-directory-program "/usr/local/opt/coreutils/libexec/gnubin/ls")
    (setq dired-listing-switches "-lXGh --group-directories-first")
    (add-hook 'dired-mode-hook 'dired-omit-mode)
    (add-hook 'dired-mode-hook 'dired-hide-details-mode)))

This configuration is for OS X. Notice that I use GNU ls rather than the ls that ships with OS X as it doesn't support the command line options we need for this. You can get this by running brew install coreutils

Now we have a dired buffer with the functionality we want. To solve the last two requirements we use two very handy Emacs features: Dedicated Windows and Action Functions for display-buffer.

(defun mhj/toggle-project-explorer ()
  "Toggle the project explorer window."
  (let* ((buffer (dired-noselect (projectile-project-root)))
	(window (get-buffer-window buffer)))
    (if window

(defun mhj/show-project-explorer ()
  "Project dired buffer on the side of the frame.
Shows the projectile root folder using dired on the left side of
the frame and makes it a dedicated window for that buffer."
  (let ((buffer (dired-noselect (projectile-project-root))))
      (display-buffer-in-side-window buffer '((side . left) (window-width . 0.2)))
      (set-window-dedicated-p (get-buffer-window buffer) t))))

(defun mhj/hide-project-explorer ()
  "Hide the project-explorer window."
  (let ((buffer (dired-noselect (projectile-project-root))))
      (delete-window (get-buffer-window buffer))
      (kill-buffer buffer))))

The interesting functions here are display-buffer-in-side-window and set-window-dedicated-p.

That's all it takes. I've been using it for a couple of weeks and so far I've very happy with the solution. It's pretty convenient that it's using dired as it gives you a lot of features for free and it plays well with other dired packages like dired-narrow.