Define advice for `narrow-to-region` so that it will automatically create an indirect buffer

multinarrow.lisp

;; Make narrowing nicer
; this makes sure we have a way to get the name of the current function
(which-function-mode)
(defadvice narrow-to-defun (before narrow-in-new-buffer activate)
  "When using `narrow-to-defun', narrow in an indirect buffer whose
   name is the original buffer's name augmented by the function
   being focused."
  (let ((parent-name (buffer-name))
        (name (concatenate 'string
                           (buffer-name)
                           ":"
                           (which-function))))
    (make-indirect-buffer (buffer-name) name t)
    (switch-to-buffer name)
    (make-local-variable 'destroy-and-switch-to-on-widen)
    (setq destroy-and-switch-to-on-widen parent-name)))
(defadvice widen (around destroy-indirect-narrow-buffer activate)
  (if (and (boundp 'destroy-and-switch-to-on-widen) destroy-and-switch-to-on-widen)
      (let ((next-buffer destroy-and-switch-to-on-widen))
        (kill-buffer)
        (switch-to-buffer next-buffer))
    ad-do-it))

hmmm, there should probably be a way to use which-function without requiring which-function-mode to be activated (which displays the current function name in the modeline). I am not very motivated to find it though; I usually use which-function-mode anyway.

you only need to require it to use, activation is not necesary so you can do (require 'which-func)

Even if the module is loaded, I had some problems with it failing to automatically build the imenu index the first time and I'm not sure why. I blindly activated which-function-mode to hopefully force the index to be built. Maybe it was just a fluke-y error though.