Eshell: Add comment on history uniqueness algorithm

.emacs.d/lisp/init-eshell.el

@@ -235,6 +235,10 @@ This should be faster then `seq-uniq'."
         (index 1))
     (while (<= index (1- (ring-length eshell-history-ring)))
       (if (string= first (ring-ref eshell-history-ring index))
+          ;; REVIEW: We could stop at the first match, it would be faster and it
+          ;; would eliminate duplicates if we started from a fresh history.
+          ;; From an existing history that would not clean up existing
+          ;; duplicates beyond the first one.
           (ring-remove eshell-history-ring index)
         (setq index (1+ index))))))
 (add-hook 'eshell-pre-command-hook 'ambrevar/eshell-history-remove-duplicates)