Add aggressive-indent to spacemacs layer

toggle with `t i`, disabled by default

doc/DOCUMENTATION.md

@@ -698,6 +698,7 @@ Some UI indicators can be toggled on and off (toggles start with `t`):
 <kbd>SPC t 8</kbd>    | display a mark on the 80th column
 <kbd>SPC t F</kbd>    | toggle frame fullscreen
 <kbd>SPC t f</kbd>    | toggle display of the fringe
+<kbd>SPC t i</kbd>    | toggle aggressive indent
 <kbd>SPC t l</kbd>    | toggle truncate lines
 <kbd>SPC t L</kbd>    | toggle visual lines
 <kbd>SPC t M</kbd>    | toggle frame maximize
@@ -819,6 +820,7 @@ eⓅ           | [e-project][e-project] mode
 Ⓕ            | flycheck mode
 Ⓕ2           | flymake mode
 Ⓖ            | guide-key mode
+Ⓘ            | aggressive indent mode
 (Ⓟ)          | paredit mode
 Ⓢ            | flyspell mode
 (Ⓢ)          | [smartparens][sp] mode

spacemacs/packages.el

@@ -3,6 +3,7 @@
     ac-ispell
     ace-jump-mode
     ag
+    aggressive-indent
     anzu
     auto-complete
     auto-complete-clang
@@ -143,6 +144,22 @@ which require an initialization must be listed explicitly in the list.")
       (setq ace-jump-mode-scope 'global)
       (evil-leader/set-key "`" 'ace-jump-mode-pop-mark))))
 
+(defun spacemacs/init-aggressive-indent ()
+  (use-package aggressive-indent
+    :defer t
+    :init
+    (progn
+      (defun spacemacs/toggle-aggressive-indent ()
+        "Toggle the aggressive indent mode for the current buffer."
+        (interactive)
+        (require 'aggressive-indent)
+        (if (symbol-value aggressive-indent-mode)
+            (global-aggressive-indent-mode -1)
+          (global-aggressive-indent-mode)))
+      (evil-leader/set-key "ti" 'spacemacs/toggle-aggressive-indent))
+    :config
+    (spacemacs|diminish aggressive-indent-mode " Ⓘ")))
+
 (defun spacemacs/init-anzu ()
   (use-package anzu
     :init