Adds Graphviz layer

- Uses a forked version of graphviz-dot-mode.el with a local install.
  Upstream PR: ppareit/graphviz-dot-mode#18

layers/+lang/graphviz/README.org

@@ -0,0 +1,37 @@
+#+TITLE: graphviz layer
+#+HTML_HEAD_EXTRA: <link rel="stylesheet" type="text/css" href="../css/readtheorg.css" />
+
+#+CAPTION: logo
+
+# The maximum height of the logo should be 200 pixels.
+[[img/graphviz.png]]
+
+* Table of Contents                                        :TOC_4_org:noexport:
+ - [[Description][Description]]
+ - [[Install][Install]]
+ - [[Key bindings][Key bindings]]
+
+* Description
+This contains a forked version of [[https://github.com/ppareit/graphviz-dot-mode][graphviz-dot-mode]] that enables a live-reload
+type work flow for editing `.dot` files. When live-preview is enabled, saving
+the file will automatically trigger a compilation and reload of the image buffer
+associated with the file.
+
+If the live preview is not always updating the rendered image properly, you can
+try to adjust the value of ~graphviz-dot-revert-delay~ higher to give the
+compiler more time to finish generating the file before reverting the buffer.
+
+* Install
+To use this contribution add it to your =~/.spacemacs=
+
+#+begin_src emacs-lisp
+  (setq-default dotspacemacs-configuration-layers '(graphviz))
+#+end_src
+
+* Key bindings
+| Key Binding | Description                          |
+|-------------+--------------------------------------|
+| ~<SPC> t~   | Toggle live-preview                  |
+| ~<SPC> c~   | Set compile command and compile file |
+| ~<SPC> p~   | Preview file                         |
+| ~<SPC> ,~   | Preview file                         |

layers/+lang/graphviz/packages.el

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+;;; packages.el --- graphviz layer packages file for Spacemacs.
+;;
+;; Copyright (c) 2012-2016 Sylvain Benner & Contributors
+;;
+;; This file is not part of GNU Emacs.
+;;
+;;; License: GPLv3
+
+;;; Commentary:
+
+;;; Code:
+
+(defconst graphviz-packages
+  '((graphviz-dot-mode :location (recipe :fetcher github :repo "luxbock/graphviz-dot-mode"))))
+
+(defun graphviz/init-graphviz-dot-mode ()
+  (use-package graphviz-dot-mode
+    :mode (("\\.diag$"      . graphviz-dot-mode)
+           ("\\.blockdiag$" . graphviz-dot-mode)
+           ("\\.nwdiag$"    . graphviz-dot-mode)
+           ("\\.rackdiag$"  . graphviz-dot-mode)
+           ("\\.dot$"       . graphviz-dot-mode)
+           ("\\.gv"         . graphviz-dot-mode))
+    :config
+    (progn
+      (spacemacs|add-toggle graphviz-live-reload
+        :status graphviz-dot-auto-preview-on-save
+        :on (graphviz-turn-on-live-preview)
+        :off (graphviz-turn-off-live-preview)
+        :documentation "Enable Graphviz live reload.")
+      (define-key graphviz-dot-mode-map (kbd "M-q") 'graphviz-dot-indent-graph)
+      (spacemacs/set-leader-keys-for-major-mode 'graphviz-dot-mode
+        "t" 'spacemacs/toggle-graphviz-live-reload
+        "c" 'compile
+        "p" 'graphviz-dot-preview
+        "," 'graphviz-dot-preview))))
+
+;;; packages.el ends here