gistfile1.el

;;; Problem solved, by subterfuge.
(defadvice rgrep (around rgrep-rename-previous-buffer activate compile)
  "If a previous *grep* buffer exists, offer to rename it before
running the new process."
  (interactive
   (let ((old-grep-buf (get-buffer "*grep*")))
     (if (and old-grep-buf
              (y-or-n-p "Grep results buffer already exists; rename it first? "))
         (let ((new-buf-name (read-string "New name: ")))
           (with-current-buffer old-grep-buf
             (rename-buffer new-buf-name))))
     ;; Sneaky: we need to match the interactive spec for the original
     ;; rgrep, but we also just want to use the original
     ;; interactivity.  Hence, this dummy list followed by
     ;; 'call-interactively (and no reference to ad-do-it)
     (list 'ignored-re 'ignored-files 'ignored-dirs)))
  (call-interactively 'ad-Orig-rgrep))


;;; This doesn't work: I want to advise rgrep so that if an existing
;;; set of results exists, offer the user the opportunity to rename
;;; them before they get clobbered.  Currently it errors because the
;;; argument lists don't match (due to the interactive form), but I
;;; also want to continue using the original definition's interaction,
;;; just tack some extra before it.  Can I do this?
;; (defadvice rgrep (around rgrep-rename-previous-buffer activate compile)
;;   "If a previous *grep* buffer exists, offer to rename it before
;;   running the new process."
;;   (interactive)
;;   (let ((old-grep-buf (get-buffer "*grep*")))
;;     (if (and old-grep-buf
;;              (y-or-n-p "Grep results buffer already exists; rename it first? "))
;;         (let ((new-buf-name (read-string "New name: ")))
;;           (with-current-buffer old-grep-buf
;;             (rename-buffer new-buf-name)))))
;;   (call-interactively 'ad-Orig-rgrep))