Curse that hunk!

[Alan Mackenzie <acm@muc.de>]

Hello, Emacs.

I found myself this evening trying to patch a file with a 1400 line hunk
which didn't (quite) match.  This happens to me quite often, though it's
never been as bad as a 1400 line mismatch before.

Finding the point where a patch hunk's old lines fail to match the file
being patched is tedious and error prone.  There surely ought to be a
Lisp program, perhaps in diff.el which would fine these differences.

This evening, I hacked together the following command which, though
ugly, did the job:

(defun crack-patch (p-buf s-buf)
  (interactive "b\nb")
  (let (str
        )
    (catch 'found
      (while (progn (set-buffer p-buf) (not (eobp)))
        (re-search-forward "^\\([ -]\\)\\(.*\\)$")
        (setq str (match-string-no-properties 2))
        (set-buffer s-buf)
        (message "point: %s" (point))
        (unless (looking-at (concat "^"
                                    (regexp-quote str) "$"))
          (throw 'found nil))
        (forward-line)))))

To use it, type in the p-buf, the name of the patch buffer, and s-buf,
the name of the source buffer you want to patch.  In p-buf, point should
be at the start of a context or - line, and in s-buf, point should be at
the corresponding point.  The command will run and stop at the first
discrepancy between the two.

As I say, very rough and ready, but I managed to get my 1400 line patch
hunk working with it.

Surely there ought to be some facility like this in Emacs?

-- 
Alan Mackenzie (Nuremberg, Germany).