Re Resyncing in ediff

[Doug Lewan <dougl@shubertticketing.com>]

A few days ago I asked:
> Is there a "nice" way to get ediff to resync?

Drew Adams had a suggestion that was close to what I already do: Narrow from point to end of buffer in both buffers of interest and ediff from there. Thank you Drew.

Since my current world is in C, I've written a little hack that [mostly] works for C. It works on a per function basis. It's not ideal, but it seems adequate. I freely invite anyone to turn it into something that's actually good.

,Doug

Here's the code:

;;; Commentary:

;; Sometimes ediff gets confused about which regions should correspond.
;; (This seems most common around blank or effectively blank lines.)
;; The problem really only arises from diffing long things (usually files).
;; This file contains code to help diff two things (usually files)
;; just one function at a time.

;;; Documentation:

;; To use this:
;; (1) Load this code.
;; (2) Open the two files to be diffed in exactly 2 windows.
;; (3) Put the point in the function of interest in one of those windows.
;; (4) M-x ediff-defun-at-point

;;; Code:

;; 
;; Dependencies
;;
(require 'which-func)

;; 
;; Vars
;; 
(defvar *ca-symbol-re* "\\sw\\(?:\\sw\\|\\s_\\|_\\)*"
  "RE to match a symbol in C.")

(defvar *ca-type-re*
  (concat
   "\\(?:static\\|extern\\s-+\\)?"	;Maybe it's qualified
   *ca-symbol-re* "\\s-*"		;A type
   "\\**"				;Maybe it's a pointer
   )
  "RE to match a type in a C declaration.")

;; 
;; Commands
;;

(defun narrow-to-this-defun-in-both-windows ()
  "Do that.
CAVEAT: Different packages have different ideas
about what function they're in at the beginning of a function declaration."
  (interactive)
  (let ((function-name (which-function)))
    (widen)
    (narrow-to-defun)
    (other-window 1)
    (widen)
    (goto-char (point-min))
    (if (re-search-forward (format (concat "^" *ca-type-re* "\\s-+" "%s" "\\s-*(") function-name (point-max) t))
	(narrow-to-defun)
      (error "That function doesn't exist in the other window."))
    (previous-window)))

(defun ediff-defun-at-point ()
  (interactive)
  (narrow-to-this-defun-in-both-windows)
  (ediff-buffers (window-buffer)
		 (window-buffer (next-window))))