spacemacs-core: Fix issues with major-mode-leader

Use same hook as evil-leader for major-mode-leader. This fixes an
inconsistency that could arise between the leader key being bound but
the major-mode leader key not being bound (See for example syl20bnr#3000). By
using the same hook as evil-leader-mode, we ensure that either both keys
or bound or neither.

A minor problem that was fixed was `mode-map` and `major-mode-map` were
not let bound and had global scope.

layers/+distribution/spacemacs-core/funcs.el

@@ -114,27 +114,27 @@ used as the prefix command."
 
 (defun spacemacs/activate-major-mode-leader ()
   "Bind major mode key map to `dotspacemacs-major-mode-leader-key'."
-  (setq mode-map (cdr (assoc major-mode evil-leader--mode-maps)))
-  (when mode-map
-    (setq major-mode-map (lookup-key mode-map (kbd "m")))
-    (mapc (lambda (s)
-            (eval `(define-key
-                     ,(intern (format "evil-%S-state-local-map" s))
-                     ,(kbd dotspacemacs-major-mode-leader-key)
-                     major-mode-map)))
-          '(normal motion))
-    (mapc (lambda (s)
-            (eval `(define-key
-                     ,(intern (format "evil-%S-state-local-map" s))
-                     ,(kbd dotspacemacs-major-mode-emacs-leader-key)
-                     major-mode-map)))
-          '(emacs insert normal motion visual))
-    ;; using `bound-and-true-p', because hybrid-mode may not be loaded when
-    ;; using emacs or vim style
-    (when (bound-and-true-p hybrid-mode)
-      (define-key evil-hybrid-state-map
-        (kbd dotspacemacs-major-mode-emacs-leader-key)
-        major-mode-map))))
+  (let* ((mode-map (cdr (assoc major-mode evil-leader--mode-maps)))
+         (major-mode-map (when mode-map (lookup-key mode-map (kbd "m")))))
+    (when major-mode-map
+      (mapc (lambda (s)
+              (eval `(define-key
+                       ,(intern (format "evil-%S-state-local-map" s))
+                       ,(kbd dotspacemacs-major-mode-leader-key)
+                       major-mode-map)))
+            '(normal motion))
+      (mapc (lambda (s)
+              (eval `(define-key
+                       ,(intern (format "evil-%S-state-local-map" s))
+                       ,(kbd dotspacemacs-major-mode-emacs-leader-key)
+                       major-mode-map)))
+            '(emacs insert normal motion visual))
+      ;; using `bound-and-true-p', because hybrid-mode may not be loaded when
+      ;; using emacs or vim style
+      (when (bound-and-true-p hybrid-mode)
+        (define-key evil-hybrid-state-map
+          (kbd dotspacemacs-major-mode-emacs-leader-key)
+          major-mode-map)))))
 
 (defun spacemacs/split-and-new-line ()
   "Split a quoted string or s-expression and insert a new line with

layers/+distribution/spacemacs-core/packages.el

@@ -457,8 +457,8 @@ Example: (evil-map visual \"<\" \"<gv\")"
             '(emacs insert normal visual motion))
       ;; experimental: map SPC m to ,
       (when dotspacemacs-major-mode-leader-key
-        (add-hook 'after-change-major-mode-hook
-                  'spacemacs/activate-major-mode-leader)))))
+        (add-hook 'evil-local-mode-hook
+                  'spacemacs/activate-major-mode-leader t)))))
 
 (defun spacemacs-core/init-evil-surround ()
   (use-package evil-surround