spacemacs/layers/+tools/dash/packages.el

 ;; see conditional package inclusion
(setq dash-packages '(helm-dash))

(cond
 ((spacemacs/system-is-mac)
  (push 'dash-at-point dash-packages))
 ((or (spacemacs/system-is-linux)
      (spacemacs/system-is-mswindows))
  (push 'zeal-at-point dash-packages)))

(when (configuration-layer/layer-usedp 'spacemacs-helm)
  (defun dash/init-helm-dash ()
    (use-package helm-dash
      :defer t
      :init
      (spacemacs/set-leader-keys
        "dh" 'helm-dash-at-point
        "dH" 'helm-dash)
      :config
      (defun dash//activate-package-docsets (path)
        "Add dash docsets from specified PATH."
        (setq helm-dash-docsets-path path
              helm-dash-common-docsets (helm-dash-installed-docsets))
        (message (format "activated %d docsets from: %s"
                         (length helm-dash-common-docsets) path)))
      (dash//activate-package-docsets dash-helm-dash-docset-path))))

(defun dash/init-dash-at-point ()
  (use-package dash-at-point
    :defer t
    :init
    (progn
      (spacemacs/set-leader-keys "dd" 'dash-at-point)
      (spacemacs/set-leader-keys "dD" 'dash-at-point-with-docset))))

(defun dash/init-zeal-at-point ()
  (use-package zeal-at-point
    :defer t
    :init
    (spacemacs/set-leader-keys
      "dd" 'zeal-at-point
      "dD" 'zeal-at-point-set-docset)
    :config
    ;; This lets users seach in multiple docsets
    (push '(web-mode . "html,css,javascript") zeal-at-point-mode-alist)
    ))