Add a key binding to force focus back to the minibuffer

resolves #597

doc/DOCUMENTATION.md

@@ -1175,6 +1175,7 @@ Windows manipulation commands (start with `w`):
 
 Key Binding                               |                 Description
 ------------------------------------------|----------------------------------------------------------------
+<kbd>SPC w b</kbd>                        | force the focus back to the minibuffer (usefull with `helm` popups)
 <kbd>SPC w c</kbd>                        | close a window
 <kbd>SPC w d</kbd>                        | toggle window dedication (dedicated window cannot be reused by a mode)
 <kbd>SPC w H</kbd>                        | move window to the left

spacemacs/funcs.el

@@ -820,3 +820,9 @@ If ASCII si not provided then UNICODE is used instead."
            (symbol-value flycheck-mode))
       (call-interactively 'flycheck-previous-error)
     (call-interactively 'previous-error)))
+
+(defun switch-to-minibuffer-window ()
+  "switch to minibuffer window (if active)"
+  (interactive)
+  (when (active-minibuffer-window)
+    (select-window (active-minibuffer-window))))

spacemacs/keybindings.el

@@ -230,6 +230,7 @@
   "w."  'spacemacs/window-manipulation-micro-state
   "w2"  'layout-double-columns
   "w3"  'layout-triple-columns
+  "wb"  'switch-to-minibuffer-window
   "wc"  'delete-window
   "wC"  'delete-other-windows
   "wd"  'toggle-current-window-dedication