autosave undo history

core/prelude-editor.el

@@ -57,6 +57,11 @@
 (setq auto-save-file-name-transforms
       `((".*" ,temporary-file-directory t)))
 
+;; autosave the undo-tree history
+(setq undo-tree-history-directory-alist
+      `((".*" . ,temporary-file-directory)))
+(setq undo-tree-auto-save-history t)
+
 ;; revert buffers automatically when underlying files are changed externally
 (global-auto-revert-mode t)