Fix warnings about unrecognized keys without helm or ivy layers

In perspective transient state. b and l keys in the docstring have no
corresponding functions declared whenever both helm and ivy layers are not
used.

Add two private variables to fix the issue:
- spacemacs--persp-display-buffers-func
- spacemacs--persp-display-perspectives-func

These variables are set to the correct functions by the helm and ivy layers via
a use-package hook.

Default is `ignore` function so b and l does nothing if both helm and ivy layers
are not used, TODO: we should find a better default function.

layers/+completion/helm/packages.el

@@ -709,10 +709,13 @@ Search for a search tool in the order provided by `dotspacemacs-search-tools'."
   ;;  Restore popwin-mode after a Helm session finishes.
   (add-hook 'helm-cleanup-hook #'spacemacs//helm-restore-display))
 
+(defun helm/pre-init-persp-mode ()
+  (spacemacs|use-package-add-hook persp-mode
+    :post-config
+    (setq
+     spacemacs--persp-display-buffers-func 'spacemacs/persp-helm-mini
+     spacemacs--persp-display-perspectives-func 'spacemacs/helm-perspectives)))
+
 (defun helm/post-init-projectile ()
   (setq projectile-completion-system 'helm))
 
-(defun helm/post-init-persp-mode ()
-  (spacemacs/transient-state-register-add-bindings 'layouts
-    '(("b" spacemacs/persp-helm-mini :exit t)
-      ("l" spacemacs/helm-perspectives :exit t))))

layers/+completion/ivy/packages.el

@@ -214,6 +214,13 @@
   (use-package ivy-hydra)
   (define-key hydra-ivy/keymap [escape] 'hydra-ivy/keyboard-escape-quit-and-exit))
 
+(defun ivy/pre-init-persp-mode ()
+  (spacemacs|use-package-add-hook presp-mode
+    :post-config
+    (setq
+     spacemacs--persp-display-buffers-func 'spacemacs/ivy-spacemacs-layout-buffer
+     spacemacs--persp-display-perspectives-func 'spacemacs/ivy-spacemacs-layouts)))
+
 (defun ivy/post-init-persp-mode ()
   ;; based on https://gist.github.com/Bad-ptr/1aca1ec54c3bdb2ee80996eb2b68ad2d#file-persp-ivy-el
   (add-hook 'ivy-ignore-buffers #'spacemacs//layout-not-contains-buffer-p)
@@ -230,12 +237,12 @@
    'spacemacs/ivy-spacemacs-layouts
    '(("c" persp-kill-without-buffers "Close layout(s)")
      ("k" persp-kill  "Kill layout(s)")))
+  ;; TODO: better handling of C and X bindings for ivy
+  ;;       check ivy/pre-init-persp-mode
   (spacemacs/transient-state-register-remove-bindings 'layouts
     '("C" "X"))
   (spacemacs/transient-state-register-add-bindings 'layouts
-    '(("b" spacemacs/ivy-spacemacs-layout-buffer :exit t)
-      ("l" spacemacs/ivy-spacemacs-layouts :exit t)
-      ("C" spacemacs/ivy-spacemacs-layout-close-other :exit t)
+    '(("C" spacemacs/ivy-spacemacs-layout-close-other :exit t)
       ("X" spacemacs/ivy-spacemacs-layout-kill-other :exit t))))
 
 (defun ivy/post-init-projectile ()

layers/+spacemacs/spacemacs-layouts/funcs.el

@@ -59,6 +59,20 @@ Cancels autosave on exiting perspectives mode."
 
 ;; Persp transient-state
 
+(defvar spacemacs--persp-display-buffers-func 'ignore
+  "Function to display buffers in the prespective.")
+(defun spacemacs/presp-buffers ()
+  "Call the function defined in `spacemacs--persp-display-buffers-func'"
+  (interactive)
+  (call-interactively spacemacs--persp-display-buffers-func))
+
+(defvar spacemacs--persp-display-perspectives-func 'ignore
+  "Function to display perspectives.")
+(defun spacemacs/presp-buffers ()
+  "Call the function defined in `spacemacs--persp-display-perspectives-func'"
+  (interactive)
+  (call-interactively spacemacs--persp-display-perspectives-func))
+
 (defun spacemacs//layouts-ts-toggle-hint ()
   "Toggle the full hint docstring for the layouts transient-state."
   (interactive)

layers/+spacemacs/spacemacs-layouts/packages.el

@@ -188,10 +188,12 @@
         ("C-l" persp-next)
         ("a" persp-add-buffer :exit t)
         ("A" persp-import-buffers :exit t)
+        ("b" spacemacs/presp-buffers :exit t)
         ("d" spacemacs/layouts-ts-close)
         ("D" spacemacs/layouts-ts-close-other :exit t)
         ("h" spacemacs/layout-goto-default :exit t)
         ("L" persp-load-state-from-file :exit t)
+        ("l" spacemacs/presp-perspectives :exit t)
         ("n" persp-next)
         ("N" persp-prev)
         ("o" spacemacs/select-custom-layout :exit t)