Copyright © 2018 Oleg Pykhalov <go.wigust@gmail.com>

This patch adds a support for :which key.

*** a/bind-key.el	1970-01-01 03:00:01.000000000 +0300
--- b/bind-key.el	2018-02-11 00:23:34.858160456 +0300
***************
*** 217,222 ****
--- 217,223 ----
           (filter (plist-get args :filter))
           (menu-name (plist-get args :menu-name))
           (pkg (plist-get args :package))
+          (which (plist-get args :which))
           (key-bindings (progn
                           (while (keywordp (car args))
                             (pop args)
***************
*** 254,259 ****
--- 255,262 ----
               ,@(if menu-name
                     `((define-prefix-command ',prefix-map nil ,menu-name))
                   `((define-prefix-command ',prefix-map)))
+              ,@(if which
+                    `((which-key-add-key-based-replacements ,prefix ',which)))
               ,@(if (and map (not (eq map 'global-map)))
                     (wrap map `((bind-key ,prefix ',prefix-map ,map ,filter)))
                   `((bind-key ,prefix ',prefix-map nil ,filter)))))