Hack to make “adaptive-wrap-prefix-mode” work with tabs and show a fill indicator.

adaptive-wrap-fill-context-prefix

(defun adaptive-wrap-fill-context-prefix (begin end)
  "Like `fill-context-prefix', but with length adjusted by `adaptive-wrap-extra-indent'."
  ;; Note: fill-context-prefix may return nil; See:
  ;; http://article.gmane.org/gmane.emacs.devel/156285
  (let* ((fcp (or (fill-context-prefix begin end) ""))
         (fcp-len (string-width fcp)))
    (if (>= adaptive-wrap-extra-indent 0)
        (concat (make-string fcp-len ?\ )
                "│"
                (make-string adaptive-wrap-extra-indent ?\ ))
      "")))