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;;; diff-mode.el --- a mode for viewing/editing context diffs
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;; Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004,
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;;   2005, 2006, 2007 Free Software Foundation, Inc.
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;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
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;; Keywords: convenience patch diff
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;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
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;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.
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;;; Commentary:

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;; Provides support for font-lock, outline, navigation
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;; commands, editing and various conversions as well as jumping
;; to the corresponding source file.

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;; Inspired by Pavel Machek's patch-mode.el (<pavel@@atrey.karlin.mff.cuni.cz>)
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;; Some efforts were spent to have it somewhat compatible with XEmacs'
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;; diff-mode as well as with compilation-minor-mode

;; Bugs:

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;; - Reverse doesn't work with normal diffs.
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;; Todo:

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;; - Add a `delete-after-apply' so C-c C-a automatically deletes hunks.
;;   Also allow C-c C-a to delete already-applied hunks.
;;
;; - Try `diff <file> <hunk>' to try and fuzzily discover the source location
;;   of a hunk.  Show then the changes between <file> and <hunk> and make it
;;   possible to apply them to <file>, <hunk-src>, or <hunk-dst>.
;;   Or maybe just make it into a ".rej to diff3-markers converter".
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;;   Maybe just use `wiggle' (by Neil Brown) to do it for us.
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;;
;; - Refine hunk on a word-by-word basis.
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;; 
;; - in diff-apply-hunk, strip context in replace-match to better
;;   preserve markers and spacing.
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;; - Handle `diff -b' output in context->unified.
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;;; Code:
(eval-when-compile (require 'cl))

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(defvar add-log-buffer-file-name-function)

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(defgroup diff-mode ()
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  "Major mode for viewing/editing diffs."
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  :version "21.1"
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  :group 'tools
  :group 'diff)

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(defcustom diff-default-read-only nil
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  "If non-nil, `diff-mode' buffers default to being read-only."
  :type 'boolean
  :group 'diff-mode)

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(defcustom diff-jump-to-old-file nil
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  "*Non-nil means `diff-goto-source' jumps to the old file.
Else, it jumps to the new file."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-update-on-the-fly t
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  "*Non-nil means hunk headers are kept up-to-date on-the-fly.
When editing a diff file, the line numbers in the hunk headers
need to be kept consistent with the actual diff.  This can
either be done on the fly (but this sometimes interacts poorly with the
undo mechanism) or whenever the file is written (can be slow
when editing big diffs)."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-advance-after-apply-hunk t
  "*Non-nil means `diff-apply-hunk' will move to the next hunk after applying."
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  :type 'boolean
  :group 'diff-mode)
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(defcustom diff-mode-hook nil
  "Run after setting up the `diff-mode' major mode."
  :type 'hook
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  :options '(diff-delete-empty-files diff-make-unified)
  :group 'diff-mode)
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(defvar diff-outline-regexp
  "\\([*+][*+][*+] [^0-9]\\|@@ ...\\|\\*\\*\\* [0-9].\\|--- [0-9]..\\)")

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;;;;
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;;;; keymap, menu, ...
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;;;;
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(easy-mmode-defmap diff-mode-shared-map
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  '(;; From Pavel Machek's patch-mode.
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    ("n" . diff-hunk-next)
    ("N" . diff-file-next)
    ("p" . diff-hunk-prev)
    ("P" . diff-file-prev)
    ("k" . diff-hunk-kill)
    ("K" . diff-file-kill)
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    ;; From compilation-minor-mode.
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    ("}" . diff-file-next)
    ("{" . diff-file-prev)
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    ("\C-m" . diff-goto-source)
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    ([mouse-2] . diff-goto-source)
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    ;; From XEmacs' diff-mode.
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    ;; Standard M-w is useful, so don't change M-W.
    ;;("W" . widen)
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    ;;("." . diff-goto-source)		;display-buffer
    ;;("f" . diff-goto-source)		;find-file
    ("o" . diff-goto-source)		;other-window
    ;;("w" . diff-goto-source)		;other-frame
    ;;("N" . diff-narrow)
    ;;("h" . diff-show-header)
    ;;("j" . diff-show-difference)	;jump to Nth diff
    ;;("q" . diff-quit)
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    ;; Not useful if you have to metafy them.
    ;;(" " . scroll-up)
    ;;("\177" . scroll-down)
    ;; Standard M-a is useful, so don't change M-A.
    ;;("A" . diff-ediff-patch)
    ;; Standard M-r is useful, so don't change M-r or M-R.
    ;;("r" . diff-restrict-view)
    ;;("R" . diff-reverse-direction)
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    ("q" . quit-window))
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  "Basic keymap for `diff-mode', bound to various prefix keys.")
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(easy-mmode-defmap diff-mode-map
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  `(("\e" . ,diff-mode-shared-map)
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    ;; From compilation-minor-mode.
    ("\C-c\C-c" . diff-goto-source)
    ;; Misc operations.
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    ("\C-c\C-a" . diff-apply-hunk)
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    ("\C-c\C-e" . diff-ediff-patch)
    ("\C-c\C-n" . diff-restrict-view)
    ("\C-c\C-r" . diff-reverse-direction)
    ("\C-c\C-s" . diff-split-hunk)
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    ("\C-c\C-t" . diff-test-hunk)
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    ("\C-c\C-u" . diff-context->unified)
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    ;; `d' because it duplicates the context :-(  --Stef
    ("\C-c\C-d" . diff-unified->context)
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    ("\C-c\C-w" . diff-refine-hunk)
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    ("\C-c\C-f" . next-error-follow-minor-mode))
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  "Keymap for `diff-mode'.  See also `diff-mode-shared-map'.")

(easy-menu-define diff-mode-menu diff-mode-map
  "Menu for `diff-mode'."
  '("Diff"
    ["Jump to Source"		diff-goto-source	t]
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    ["Apply hunk"		diff-apply-hunk		t]
    ["Apply diff with Ediff"	diff-ediff-patch	t]
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    ["-----" nil nil]
    ["Reverse direction"	diff-reverse-direction	t]
    ["Context -> Unified"	diff-context->unified	t]
    ["Unified -> Context"	diff-unified->context	t]
    ;;["Fixup Headers"		diff-fixup-modifs	(not buffer-read-only)]
    ))

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(defcustom diff-minor-mode-prefix "\C-c="
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  "Prefix key for `diff-minor-mode' commands."
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  :type '(choice (string "\e") (string "C-c=") string)
  :group 'diff-mode)
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(easy-mmode-defmap diff-minor-mode-map
  `((,diff-minor-mode-prefix . ,diff-mode-shared-map))
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  "Keymap for `diff-minor-mode'.  See also `diff-mode-shared-map'.")

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;;;;
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;;;; font-lock support
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;;;;
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(defface diff-header
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  '((((class color) (min-colors 88) (background light))
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     :background "grey85")
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    (((class color) (min-colors 88) (background dark))
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     :background "grey45")
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    (((class color) (background light))
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     :foreground "blue1" :weight bold)
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    (((class color) (background dark))
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     :foreground "green" :weight bold)
    (t :weight bold))
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  "`diff-mode' face inherited by hunk and index header faces."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-header-face 'face-alias 'diff-header)
(defvar diff-header-face 'diff-header)
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(defface diff-file-header
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  '((((class color) (min-colors 88) (background light))
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     :background "grey70" :weight bold)
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    (((class color) (min-colors 88) (background dark))
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     :background "grey60" :weight bold)
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    (((class color) (background light))
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     :foreground "green" :weight bold)
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    (((class color) (background dark))
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     :foreground "cyan" :weight bold)
    (t :weight bold))			; :height 1.3
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  "`diff-mode' face used to highlight file header lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-file-header-face 'face-alias 'diff-file-header)
(defvar diff-file-header-face 'diff-file-header)
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(defface diff-index
  '((t :inherit diff-file-header))
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  "`diff-mode' face used to highlight index header lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-index-face 'face-alias 'diff-index)
(defvar diff-index-face 'diff-index)
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(defface diff-hunk-header
  '((t :inherit diff-header))
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  "`diff-mode' face used to highlight hunk header lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-hunk-header-face 'face-alias 'diff-hunk-header)
(defvar diff-hunk-header-face 'diff-hunk-header)
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(defface diff-removed
  '((t :inherit diff-changed))
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  "`diff-mode' face used to highlight removed lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-removed-face 'face-alias 'diff-removed)
(defvar diff-removed-face 'diff-removed)
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(defface diff-added
  '((t :inherit diff-changed))
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  "`diff-mode' face used to highlight added lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-added-face 'face-alias 'diff-added)
(defvar diff-added-face 'diff-added)
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(defface diff-changed
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  '((((type tty pc) (class color) (background light))
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     :foreground "magenta" :weight bold :slant italic)
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    (((type tty pc) (class color) (background dark))
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     :foreground "yellow" :weight bold :slant italic))
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  "`diff-mode' face used to highlight changed lines."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-changed-face 'face-alias 'diff-changed)
(defvar diff-changed-face 'diff-changed)
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(defface diff-indicator-removed
  '((t :inherit diff-removed))
  "`diff-mode' face used to highlight indicator of removed lines (-, <)."
  :group 'diff-mode
  :version "22.1")
(defvar diff-indicator-removed-face 'diff-indicator-removed)

(defface diff-indicator-added
  '((t :inherit diff-added))
  "`diff-mode' face used to highlight indicator of added lines (+, >)."
  :group 'diff-mode
  :version "22.1")
(defvar diff-indicator-added-face 'diff-indicator-added)

(defface diff-indicator-changed
  '((t :inherit diff-changed))
  "`diff-mode' face used to highlight indicator of changed lines."
  :group 'diff-mode
  :version "22.1")
(defvar diff-indicator-changed-face 'diff-indicator-changed)

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(defface diff-function
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  '((t :inherit diff-header))
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  "`diff-mode' face used to highlight function names produced by \"diff -p\"."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-function-face 'face-alias 'diff-function)
(defvar diff-function-face 'diff-function)
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(defface diff-context
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  '((((class color grayscale) (min-colors 88)) :inherit shadow))
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  "`diff-mode' face used to highlight context and other side-information."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-context-face 'face-alias 'diff-context)
(defvar diff-context-face 'diff-context)
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(defface diff-nonexistent
  '((t :inherit diff-file-header))
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  "`diff-mode' face used to highlight nonexistent files in recursive diffs."
  :group 'diff-mode)
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;; backward-compatibility alias
(put 'diff-nonexistent-face 'face-alias 'diff-nonexistent)
(defvar diff-nonexistent-face 'diff-nonexistent)
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(defconst diff-yank-handler '(diff-yank-function))
(defun diff-yank-function (text)
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  ;; FIXME: the yank-handler is now called separately on each piece of text
  ;; with a yank-handler property, so the next-single-property-change call
  ;; below will always return nil :-(   --stef
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  (let ((mixed (next-single-property-change 0 'yank-handler text))
	(start (point)))
    ;; First insert the text.
    (insert text)
    ;; If the text does not include any diff markers and if we're not
    ;; yanking back into a diff-mode buffer, get rid of the prefixes.
    (unless (or mixed (derived-mode-p 'diff-mode))
      (undo-boundary)		; Just in case the user wanted the prefixes.
      (let ((re (save-excursion
		  (if (re-search-backward "^[><!][ \t]" start t)
		      (if (eq (char-after) ?!)
			  "^[!+- ][ \t]" "^[<>][ \t]")
		    "^[ <>!+-]"))))
	(save-excursion
	  (while (re-search-backward re start t)
	    (replace-match "" t t)))))))
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(defvar diff-font-lock-keywords
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  `(("^\\(@@ -[0-9,]+ \\+[0-9,]+ @@\\)\\(.*\\)$"          ;unified
     (1 diff-hunk-header-face) (2 diff-function-face))
    ("^\\(\\*\\{15\\}\\)\\(.*\\)$"                        ;context
     (1 diff-hunk-header-face) (2 diff-function-face))
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    ("^\\*\\*\\* .+ \\*\\*\\*\\*". diff-hunk-header-face) ;context
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    ("^--- .+ ----$"             . diff-hunk-header-face) ;context
    ("^[0-9,]+[acd][0-9,]+$"     . diff-hunk-header-face) ;normal
    ("^---$"                     . diff-hunk-header-face) ;normal
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    ("^\\(---\\|\\+\\+\\+\\|\\*\\*\\*\\) \\(\\S-+\\)\\(.*[^*-]\\)?\n"
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     (0 diff-header-face) (2 diff-file-header-face prepend))
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    ("^\\([-<]\\)\\(.*\n\\)"
     (1 diff-indicator-removed-face) (2 diff-removed-face))
    ("^\\([+>]\\)\\(.*\n\\)"
     (1 diff-indicator-added-face) (2 diff-added-face))
    ("^\\(!\\)\\(.*\n\\)"
     (1 diff-indicator-changed-face) (2 diff-changed-face))
    ("^Index: \\(.+\\).*\n"
     (0 diff-header-face) (1 diff-index-face prepend))
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    ("^Only in .*\n" . diff-nonexistent-face)
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    ("^\\(#\\)\\(.*\\)"
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     (1 font-lock-comment-delimiter-face)
     (2 font-lock-comment-face))
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    ("^[^-=+*!<>#].*\n" (0 diff-context-face))))
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(defconst diff-font-lock-defaults
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  '(diff-font-lock-keywords t nil nil nil (font-lock-multiline . nil)))
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(defvar diff-imenu-generic-expression
  ;; Prefer second name as first is most likely to be a backup or
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  ;; version-control name.  The [\t\n] at the end of the unidiff pattern
  ;; catches Debian source diff files (which lack the trailing date).
  '((nil "\\+\\+\\+\\ \\([^\t\n]+\\)[\t\n]" 1) ; unidiffs
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    (nil "^--- \\([^\t\n]+\\)\t.*\n\\*" 1))) ; context diffs

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;;;;
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;;;; Movement
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;;;;
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(defconst diff-hunk-header-re "^\\(@@ -[0-9,]+ \\+[0-9,]+ @@.*\\|\\*\\{15\\}.*\n\\*\\*\\* .+ \\*\\*\\*\\*\\|[0-9]+\\(,[0-9]+\\)?[acd][0-9]+\\(,[0-9]+\\)?\\)$")
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(defconst diff-file-header-re (concat "^\\(--- .+\n\\+\\+\\+ \\|\\*\\*\\* .+\n--- \\|[^-+!<>0-9@* ]\\).+\n" (substring diff-hunk-header-re 1)))
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(defvar diff-narrowed-to nil)

(defun diff-end-of-hunk (&optional style)
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  (when (looking-at diff-hunk-header-re)
    (unless style
      ;; Especially important for unified (because headers are ambiguous).
      (setq style (cdr (assq (char-after) '((?@ . unified) (?* . context))))))
    (goto-char (match-end 0)))
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  (let ((end (and (re-search-forward (case style
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				       ;; A `unified' header is ambiguous.
				       (unified (concat "^[^-+# \\]\\|"
							diff-file-header-re))
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				       (context "^[^-+#! \\]")
				       (normal "^[^<>#\\]")
				       (t "^[^-+#!<> \\]"))
				     nil t)
		  (match-beginning 0))))
    ;; The return value is used by easy-mmode-define-navigation.
    (goto-char (or end (point-max)))))
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(defun diff-beginning-of-hunk ()
  (beginning-of-line)
  (unless (looking-at diff-hunk-header-re)
    (forward-line 1)
    (condition-case ()
	(re-search-backward diff-hunk-header-re)
      (error (error "Can't find the beginning of the hunk")))))

(defun diff-beginning-of-file ()
  (beginning-of-line)
  (unless (looking-at diff-file-header-re)
    (forward-line 2)
    (condition-case ()
	(re-search-backward diff-file-header-re)
      (error (error "Can't find the beginning of the file")))))

(defun diff-end-of-file ()
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  (re-search-forward "^[-+#!<>0-9@* \\]" nil t)
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  (re-search-forward (concat "^[^-+#!<>0-9@* \\]\\|" diff-file-header-re)
		     nil 'move)
  (if (match-beginning 1)
      (goto-char (match-beginning 1))
    (beginning-of-line)))
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;; Define diff-{hunk,file}-{prev,next}
(easy-mmode-define-navigation
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 diff-hunk diff-hunk-header-re "hunk" diff-end-of-hunk diff-restrict-view)
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(easy-mmode-define-navigation
 diff-file diff-file-header-re "file" diff-end-of-hunk)
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(defun diff-restrict-view (&optional arg)
  "Restrict the view to the current hunk.
If the prefix ARG is given, restrict the view to the current file instead."
  (interactive "P")
  (save-excursion
    (if arg (diff-beginning-of-file) (diff-beginning-of-hunk))
    (narrow-to-region (point)
		      (progn (if arg (diff-end-of-file) (diff-end-of-hunk))
			     (point)))
    (set (make-local-variable 'diff-narrowed-to) (if arg 'file 'hunk))))


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(defun diff-hunk-kill ()
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  "Kill current hunk."
  (interactive)
  (diff-beginning-of-hunk)
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  (let* ((start (point))
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	 (nexthunk (when (re-search-forward diff-hunk-header-re nil t)
		     (match-beginning 0)))
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	 (firsthunk (ignore-errors
		      (goto-char start)
		      (diff-beginning-of-file) (diff-hunk-next) (point)))
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	 (nextfile (ignore-errors (diff-file-next) (point)))
	 (inhibit-read-only t))
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    (goto-char start)
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    (if (and firsthunk (= firsthunk start)
	     (or (null nexthunk)
		 (and nextfile (> nexthunk nextfile))))
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	;; It's the only hunk for this file, so kill the file.
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	(diff-file-kill)
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      (diff-end-of-hunk)
      (kill-region start (point)))))

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(defun diff-file-kill ()
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  "Kill current file's hunks."
  (interactive)
  (diff-beginning-of-file)
  (let* ((start (point))
	 (prevhunk (save-excursion
		     (ignore-errors
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		       (diff-hunk-prev) (point))))
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	 (index (save-excursion
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		  (re-search-backward "^Index: " prevhunk t)))
	 (inhibit-read-only t))
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    (when index (setq start index))
    (diff-end-of-file)
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    (if (looking-at "^\n") (forward-char 1)) ;`tla' generates such diffs.
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    (kill-region start (point))))

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(defun diff-kill-junk ()
  "Kill spurious empty diffs."
  (interactive)
  (save-excursion
    (let ((inhibit-read-only t))
      (goto-char (point-min))
      (while (re-search-forward (concat "^\\(Index: .*\n\\)"
					"\\([^-+!* <>].*\n\\)*?"
					"\\(\\(Index:\\) \\|"
					diff-file-header-re "\\)")
				nil t)
	(delete-region (if (match-end 4) (match-beginning 0) (match-end 1))
		       (match-beginning 3))
	(beginning-of-line)))))

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(defun diff-count-matches (re start end)
  (save-excursion
    (let ((n 0))
      (goto-char start)
      (while (re-search-forward re end t) (incf n))
      n)))

(defun diff-split-hunk ()
  "Split the current (unified diff) hunk at point into two hunks."
  (interactive)
  (beginning-of-line)
  (let ((pos (point))
	(start (progn (diff-beginning-of-hunk) (point))))
    (unless (looking-at "@@ -\\([0-9]+\\),[0-9]+ \\+\\([0-9]+\\),[0-9]+ @@")
      (error "diff-split-hunk only works on unified context diffs"))
    (forward-line 1)
    (let* ((start1 (string-to-number (match-string 1)))
	   (start2 (string-to-number (match-string 2)))
	   (newstart1 (+ start1 (diff-count-matches "^[- \t]" (point) pos)))
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	   (newstart2 (+ start2 (diff-count-matches "^[+ \t]" (point) pos)))
	   (inhibit-read-only t))
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      (goto-char pos)
      ;; Hopefully the after-change-function will not screw us over.
      (insert "@@ -" (number-to-string newstart1) ",1 +"
	      (number-to-string newstart2) ",1 @@\n")
      ;; Fix the original hunk-header.
      (diff-fixup-modifs start pos))))
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;;;;
;;;; jump to other buffers
;;;;

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(defvar diff-remembered-files-alist nil)

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(defun diff-filename-drop-dir (file)
  (when (string-match "/" file) (substring file (match-end 0))))

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(defun diff-merge-strings (ancestor from to)
  "Merge the diff between ANCESTOR and FROM into TO.
Returns the merged string if successful or nil otherwise.
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The strings are assumed not to contain any \"\\n\" (i.e. end of line).
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If ANCESTOR = FROM, returns TO.
If ANCESTOR = TO, returns FROM.
The heuristic is simplistic and only really works for cases
like \(diff-merge-strings \"b/foo\" \"b/bar\" \"/a/c/foo\")."
  ;; Ideally, we want:
  ;;   AMB ANB CMD -> CND
  ;; but that's ambiguous if `foo' or `bar' is empty:
  ;; a/foo a/foo1 b/foo.c -> b/foo1.c but not 1b/foo.c or b/foo.c1
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  (let ((str (concat ancestor "\n" from "\n" to)))
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    (when (and (string-match (concat
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			      "\\`\\(.*?\\)\\(.*\\)\\(.*\\)\n"
			      "\\1\\(.*\\)\\3\n"
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			      "\\(.*\\(\\2\\).*\\)\\'") str)
	       (equal to (match-string 5 str)))
      (concat (substring str (match-beginning 5) (match-beginning 6))
	      (match-string 4 str)
	      (substring str (match-end 6) (match-end 5))))))

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(defun diff-tell-file-name (old name)
  "Tell Emacs where the find the source file of the current hunk.
If the OLD prefix arg is passed, tell the file NAME of the old file."
  (interactive
   (let* ((old current-prefix-arg)
	  (fs (diff-hunk-file-names current-prefix-arg)))
     (unless fs (error "No file name to look for"))
     (list old (read-file-name (format "File for %s: " (car fs))
			       nil (diff-find-file-name old) t))))
  (let ((fs (diff-hunk-file-names old)))
    (unless fs (error "No file name to look for"))
    (push (cons fs name) diff-remembered-files-alist)))
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(defun diff-hunk-file-names (&optional old)
  "Give the list of file names textually mentioned for the current hunk."
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  (save-excursion
    (unless (looking-at diff-file-header-re)
      (or (ignore-errors (diff-beginning-of-file))
	  (re-search-forward diff-file-header-re nil t)))
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    (let ((limit (save-excursion
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		   (condition-case ()
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		       (progn (diff-hunk-prev) (point))
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		     (error (point-min)))))
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	  (header-files
	   (if (looking-at "[-*][-*][-*] \\(\\S-+\\)\\(\\s-.*\\)?\n[-+][-+][-+] \\(\\S-+\\)")
	       (list (if old (match-string 1) (match-string 3))
		     (if old (match-string 3) (match-string 1)))
	     (forward-line 1) nil)))
      (delq nil
	    (append
	     (when (and (not old)
			(save-excursion
			  (re-search-backward "^Index: \\(.+\\)" limit t)))
	       (list (match-string 1)))
	     header-files
	     (when (re-search-backward
		    "^diff \\(-\\S-+ +\\)*\\(\\S-+\\)\\( +\\(\\S-+\\)\\)?"
		    nil t)
	       (list (if old (match-string 2) (match-string 4))
		     (if old (match-string 4) (match-string 2)))))))))

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(defun diff-find-file-name (&optional old prefix)
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  "Return the file corresponding to the current patch.
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Non-nil OLD means that we want the old file.
PREFIX is only used internally: don't use it."
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  (save-excursion
    (unless (looking-at diff-file-header-re)
      (or (ignore-errors (diff-beginning-of-file))
	  (re-search-forward diff-file-header-re nil t)))
    (let ((fs (diff-hunk-file-names old)))
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      (if prefix (setq fs (mapcar (lambda (f) (concat prefix f)) fs)))
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      (or
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       ;; use any previously used preference
       (cdr (assoc fs diff-remembered-files-alist))
       ;; try to be clever and use previous choices as an inspiration
       (dolist (rf diff-remembered-files-alist)
	 (let ((newfile (diff-merge-strings (caar rf) (car fs) (cdr rf))))
	   (if (and newfile (file-exists-p newfile)) (return newfile))))
       ;; look for each file in turn.  If none found, try again but
       ;; ignoring the first level of directory, ...
       (do* ((files fs (delq nil (mapcar 'diff-filename-drop-dir files)))
	     (file nil nil))
	   ((or (null files)
		(setq file (do* ((files files (cdr files))
				 (file (car files) (car files)))
			       ((or (null file) (file-exists-p file))
				file))))
	    file))
       ;; <foo>.rej patches implicitly apply to <foo>
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       (and (string-match "\\.rej\\'" (or buffer-file-name ""))
	    (let ((file (substring buffer-file-name 0 (match-beginning 0))))
	      (when (file-exists-p file) file)))
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       ;; If we haven't found the file, maybe it's because we haven't paid
       ;; attention to the PCL-CVS hint.
       (and (not prefix)
	    (boundp 'cvs-pcl-cvs-dirchange-re)
	    (save-excursion
	      (re-search-backward cvs-pcl-cvs-dirchange-re nil t))
	    (diff-find-file-name old (match-string 1)))
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       ;; if all else fails, ask the user
       (let ((file (read-file-name (format "Use file %s: " (or (first fs) ""))
				   nil (first fs) t (first fs))))
	 (set (make-local-variable 'diff-remembered-files-alist)
	      (cons (cons fs file) diff-remembered-files-alist))
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	 file)))))

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(defun diff-ediff-patch ()
  "Call `ediff-patch-file' on the current buffer."
  (interactive)
  (condition-case err
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      (ediff-patch-file nil (current-buffer))
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    (wrong-number-of-arguments (ediff-patch-file))))

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;;;;
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;;;; Conversion functions
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;;;;
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;;(defvar diff-inhibit-after-change nil
;;  "Non-nil means inhibit `diff-mode's after-change functions.")

(defun diff-unified->context (start end)
  "Convert unified diffs to context diffs.
START and END are either taken from the region (if a prefix arg is given) or
else cover the whole bufer."
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  (interactive (if (or current-prefix-arg (and transient-mark-mode mark-active))
		   (list (region-beginning) (region-end))
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		 (list (point-min) (point-max))))
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  (unless (markerp end) (setq end (copy-marker end t)))
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  (let (;;(diff-inhibit-after-change t)
	(inhibit-read-only t))
    (save-excursion
      (goto-char start)
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      (while (and (re-search-forward "^\\(\\(---\\) .+\n\\(\\+\\+\\+\\) .+\\|@@ -\\([0-9]+\\),\\([0-9]+\\) \\+\\([0-9]+\\),\\([0-9]+\\) @@.*\\)$" nil t)
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		  (< (point) end))
	(combine-after-change-calls
	  (if (match-beginning 2)
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	      ;; we matched a file header
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	      (progn
		;; use reverse order to make sure the indices are kept valid
		(replace-match "---" t t nil 3)
		(replace-match "***" t t nil 2))
	    ;; we matched a hunk header
	    (let ((line1 (match-string 4))
		  (lines1 (match-string 5))
		  (line2 (match-string 6))
		  (lines2 (match-string 7)))
	      (replace-match
	       (concat "***************\n*** " line1 ","
		       (number-to-string (+ (string-to-number line1)
					    (string-to-number lines1)
					    -1)) " ****"))
	      (forward-line 1)
	      (save-restriction
		(narrow-to-region (point)
				  (progn (diff-end-of-hunk 'unified) (point)))
		(let ((hunk (buffer-string)))
		  (goto-char (point-min))
		  (if (not (save-excursion (re-search-forward "^-" nil t)))
		      (delete-region (point) (point-max))
		    (goto-char (point-max))
		    (let ((modif nil) last-pt)
		      (while (progn (setq last-pt (point))
				    (= (forward-line -1) 0))
			(case (char-after)
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			  (?\s (insert " ") (setq modif nil) (backward-char 1))
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			  (?+ (delete-region (point) last-pt) (setq modif t))
			  (?- (if (not modif)
				  (progn (forward-char 1)
					 (insert " "))
				(delete-char 1)
				(insert "! "))
			      (backward-char 2))
			  (?\\ (when (save-excursion (forward-line -1)
						     (= (char-after) ?+))
				 (delete-region (point) last-pt) (setq modif t)))
			  (t (setq modif nil))))))
		  (goto-char (point-max))
		  (save-excursion
		    (insert "--- " line2 ","
			    (number-to-string (+ (string-to-number line2)
						 (string-to-number lines2)
						 -1)) " ----\n" hunk))
		  ;;(goto-char (point-min))
		  (forward-line 1)
		  (if (not (save-excursion (re-search-forward "^+" nil t)))
		      (delete-region (point) (point-max))
		    (let ((modif nil) (delete nil))
		      (while (not (eobp))
			(case (char-after)
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			  (?\s (insert " ") (setq modif nil) (backward-char 1))
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			  (?- (setq delete t) (setq modif t))
			  (?+ (if (not modif)
				  (progn (forward-char 1)
					 (insert " "))
				(delete-char 1)
				(insert "! "))
			      (backward-char 2))
			  (?\\ (when (save-excursion (forward-line 1)
						     (not (eobp)))
				 (setq delete t) (setq modif t)))
			  (t (setq modif nil)))
			(let ((last-pt (point)))
			  (forward-line 1)
			  (when delete
			    (delete-region last-pt (point))
			    (setq delete nil)))))))))))))))

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(defun diff-context->unified (start end &optional to-context)
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  "Convert context diffs to unified diffs.
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START and END are either taken from the region
\(when it is highlighted) or else cover the whole buffer.
With a prefix argument, convert unified format to context format."
  (interactive (if (and transient-mark-mode mark-active)
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		   (list (region-beginning) (region-end) current-prefix-arg)
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		 (list (point-min) (point-max) current-prefix-arg)))
  (if to-context
      (diff-unified->context start end)
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    (unless (markerp end) (setq end (copy-marker end t)))
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    (let ( ;;(diff-inhibit-after-change t)
	  (inhibit-read-only t))
      (save-excursion
	(goto-char start)
	(while (and (re-search-forward "^\\(\\(\\*\\*\\*\\) .+\n\\(---\\) .+\\|\\*\\{15\\}.*\n\\*\\*\\* \\([0-9]+\\),\\(-?[0-9]+\\) \\*\\*\\*\\*\\)$" nil t)
		    (< (point) end))
	  (combine-after-change-calls
	    (if (match-beginning 2)
		;; we matched a file header
		(progn
		  ;; use reverse order to make sure the indices are kept valid
		  (replace-match "+++" t t nil 3)
		  (replace-match "---" t t nil 2))
	      ;; we matched a hunk header
	      (let ((line1s (match-string 4))
		    (line1e (match-string 5))
		    (pt1 (match-beginning 0)))
		(replace-match "")
		(unless (re-search-forward
			 "^--- \\([0-9]+\\),\\(-?[0-9]+\\) ----$" nil t)
		  (error "Can't find matching `--- n1,n2 ----' line"))
		(let ((line2s (match-string 1))
		      (line2e (match-string 2))
		      (pt2 (progn
			     (delete-region (progn (beginning-of-line) (point))
					    (progn (forward-line 1) (point)))
			     (point-marker))))
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		  (goto-char pt1)
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		  (forward-line 1)
		  (while (< (point) pt2)
		    (case (char-after)
		      ((?! ?-) (delete-char 2) (insert "-") (forward-line 1))
		      (?\s     ;merge with the other half of the chunk
		       (let* ((endline2
			       (save-excursion
				 (goto-char pt2) (forward-line 1) (point)))
			      (c (char-after pt2)))
			 (case c
			   ((?! ?+)
			    (insert "+"
				    (prog1 (buffer-substring (+ pt2 2) endline2)
				      (delete-region pt2 endline2))))
			   (?\s		;FIXME: check consistency
			    (delete-region pt2 endline2)
			    (delete-char 1)
			    (forward-line 1))
			   (?\\ (forward-line 1))
			   (t (delete-char 1) (forward-line 1)))))
		      (t (forward-line 1))))
		  (while (looking-at "[+! ] ")
		    (if (/= (char-after) ?!) (forward-char 1)
		      (delete-char 1) (insert "+"))
		    (delete-char 1) (forward-line 1))
		  (save-excursion
		    (goto-char pt1)
		    (insert "@@ -" line1s ","
			    (number-to-string (- (string-to-number line1e)
						 (string-to-number line1s)
						 -1))
			    " +" line2s ","
			    (number-to-string (- (string-to-number line2e)
						 (string-to-number line2s)
						 -1)) " @@")))))))))))
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(defun diff-reverse-direction (start end)
  "Reverse the direction of the diffs.
START and END are either taken from the region (if a prefix arg is given) or
else cover the whole bufer."
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  (interactive (if (or current-prefix-arg (and transient-mark-mode mark-active))
		   (list (region-beginning) (region-end))
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		 (list (point-min) (point-max))))
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  (unless (markerp end) (setq end (copy-marker end t)))
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  (let (;;(diff-inhibit-after-change t)
	(inhibit-read-only t))
    (save-excursion
      (goto-char start)
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      (while (and (re-search-forward "^\\(\\([-*][-*][-*] \\)\\(.+\\)\n\\([-+][-+][-+] \\)\\(.+\\)\\|\\*\\{15\\}.*\n\\*\\*\\* \\(.+\\) \\*\\*\\*\\*\\|@@ -\\([0-9,]+\\) \\+\\([0-9,]+\\) @@.*\\)$" nil t)
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		  (< (point) end))
	(combine-after-change-calls
	  (cond
	   ;; a file header
	   ((match-beginning 2) (replace-match "\\2\\5\n\\4\\3" nil))
	   ;; a context-diff hunk header
	   ((match-beginning 6)
	    (let ((pt-lines1 (match-beginning 6))
		  (lines1 (match-string 6)))
	      (replace-match "" nil nil nil 6)
	      (forward-line 1)
	      (let ((half1s (point)))
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		(while (looking-at "[-! \\][ \t]\\|#")
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		  (when (= (char-after) ?-) (delete-char 1) (insert "+"))
		  (forward-line 1))
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		(let ((half1 (delete-and-extract-region half1s (point))))
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		  (unless (looking-at "^--- \\([0-9]+,-?[0-9]+\\) ----$")
		    (insert half1)
		    (error "Can't find matching `--- n1,n2 ----' line"))
		  (let ((str1 (match-string 1)))
		    (replace-match lines1 nil nil nil 1)
		    (forward-line 1)
		    (let ((half2s (point)))
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		      (while (looking-at "[!+ \\][ \t]\\|#")
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			(when (= (char-after) ?+) (delete-char 1) (insert "-"))
			(forward-line 1))
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		      (let ((half2 (delete-and-extract-region half2s (point))))
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			(insert (or half1 ""))
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			(goto-char half1s)
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			(insert (or half2 ""))))
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		    (goto-char pt-lines1)
		    (insert str1))))))
	   ;; a unified-diff hunk header
	   ((match-beginning 7)
	    (replace-match "@@ -\\8 +\\7 @@" nil)
	    (forward-line 1)
	    (let ((c (char-after)) first last)
	      (while (case (setq c (char-after))
		       (?- (setq first (or first (point)))
			   (delete-char 1) (insert "+") t)
		       (?+ (setq last (or last (point)))
			   (delete-char 1) (insert "-") t)
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		       ((?\\ ?#) t)
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		       (t (when (and first last (< first last))
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			    (insert (delete-and-extract-region first last)))
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			  (setq first nil last nil)
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			  (equal ?\s c)))
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		(forward-line 1))))))))))

(defun diff-fixup-modifs (start end)
  "Fixup the hunk headers (in case the buffer was modified).
START and END are either taken from the region (if a prefix arg is given) or
else cover the whole bufer."
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  (interactive (if (or current-prefix-arg (and transient-mark-mode mark-active))
		   (list (region-beginning) (region-end))
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		 (list (point-min) (point-max))))
  (let ((inhibit-read-only t))
    (save-excursion
      (goto-char end) (diff-end-of-hunk)
      (let ((plus 0) (minus 0) (space 0) (bang 0))
	(while (and (= (forward-line -1) 0) (<= start (point)))
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	  (if (not (looking-at
		    (concat "@@ -[0-9,]+ \\+[0-9,]+ @@"
			    "\\|[-*][-*][-*] [0-9,]+ [-*][-*][-*][-*]$"
			    "\\|--- .+\n\\+\\+\\+ ")))
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	      (case (char-after)
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		(?\s (incf space))
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		(?+ (incf plus))
		(?- (incf minus))
		(?! (incf bang))
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		((?\\ ?#) nil)
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		(t  (setq space 0 plus 0 minus 0 bang 0)))
	    (cond
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	     ((looking-at "@@ -[0-9]+,\\([0-9]*\\) \\+[0-9]+,\\([0-9]*\\) @@.*$")
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	      (let* ((old1 (match-string 1))
		     (old2 (match-string 2))
		     (new1 (number-to-string (+ space minus)))
		     (new2 (number-to-string (+ space plus))))
		(unless (string= new2 old2) (replace-match new2 t t nil 2))
		(unless (string= new1 old1) (replace-match new1 t t nil 1))))
	     ((looking-at "--- \\([0-9]+\\),\\([0-9]*\\) ----$")
	      (when (> (+ space bang plus) 0)
		(let* ((old1 (match-string 1))
		       (old2 (match-string 2))
		       (new (number-to-string
			     (+ space bang plus -1 (string-to-number old1)))))
		  (unless (string= new old2) (replace-match new t t nil 2)))))
	     ((looking-at "\\*\\*\\* \\([0-9]+\\),\\(-?[0-9]*\\) \\*\\*\\*\\*$")
	      (when (> (+ space bang minus) 0)
		(let* ((old (match-string 1))
		       (new (format
			     (concat "%0" (number-to-string (length old)) "d")
			     (+ space bang minus -1 (string-to-number old)))))
		  (unless (string= new old) (replace-match new t t nil 2))))))
	    (setq space 0 plus 0 minus 0 bang 0)))))))

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;;;;
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;;;; Hooks
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;;;;
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(defun diff-write-contents-hooks ()
  "Fixup hunk headers if necessary."
  (if (buffer-modified-p) (diff-fixup-modifs (point-min) (point-max)))
  nil)

;; It turns out that making changes in the buffer from within an
;; *-change-function is asking for trouble, whereas making them
;; from a post-command-hook doesn't pose much problems
(defvar diff-unhandled-changes nil)
(defun diff-after-change-function (beg end len)
  "Remember to fixup the hunk header.
See `after-change-functions' for the meaning of BEG, END and LEN."
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  ;; Ignoring changes when inhibit-read-only is set is strictly speaking
  ;; incorrect, but it turns out that inhibit-read-only is normally not set
  ;; inside editing commands, while it tends to be set when the buffer gets
  ;; updated by an async process or by a conversion function, both of which
  ;; would rather not be uselessly slowed down by this hook.
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  (when (and (not undo-in-progress) (not inhibit-read-only))
    (if diff-unhandled-changes
	(setq diff-unhandled-changes
	      (cons (min beg (car diff-unhandled-changes))
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		    (max end (cdr diff-unhandled-changes))))
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      (setq diff-unhandled-changes (cons beg end)))))

(defun diff-post-command-hook ()
  "Fixup hunk headers if necessary."
  (when (consp diff-unhandled-changes)
    (ignore-errors
      (save-excursion
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	(goto-char (car diff-unhandled-changes))
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	;; Maybe we've cut the end of the hunk before point.
	(if (and (bolp) (not (bobp))) (backward-char 1))
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	;; We used to fixup modifs on all the changes, but it turns out
	;; that it's safer not to do it on big changes, for example
	;; when yanking a big diff, since we might then screw up perfectly
	;; correct values.  -stef
	;; (unless (ignore-errors
	;; 	  (diff-beginning-of-hunk)
	;; 	  (save-excursion
	;; 	    (diff-end-of-hunk)
	;; 	    (> (point) (car diff-unhandled-changes))))
	;;   (goto-char (car diff-unhandled-changes))
	;; (re-search-forward diff-hunk-header-re (cdr diff-unhandled-changes))
	;;   (diff-beginning-of-hunk))
	;; (diff-fixup-modifs (point) (cdr diff-unhandled-changes))
	(diff-beginning-of-hunk)
	(when (save-excursion
		(diff-end-of-hunk)
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		(>= (point) (cdr diff-unhandled-changes)))
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	  (diff-fixup-modifs (point) (cdr diff-unhandled-changes)))))
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    (setq diff-unhandled-changes nil)))

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(defun diff-next-error (arg reset)
  ;; Select a window that displays the current buffer so that point
  ;; movements are reflected in that window.  Otherwise, the user might
  ;; never see the hunk corresponding to the source she's jumping to.
  (pop-to-buffer (current-buffer))
  (if reset (goto-char (point-min)))
  (diff-hunk-next arg)
  (diff-goto-source))
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;;;###autoload
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(define-derived-mode diff-mode fundamental-mode "Diff"
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  "Major mode for viewing/editing context diffs.
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Supports unified and context diffs as well as (to a lesser extent)
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normal diffs.
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When the buffer is read-only, the ESC prefix is not necessary.
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If you edit the buffer manually, diff-mode will try to update the hunk
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headers for you on-the-fly.

You can also switch between context diff and unified diff with \\[diff-context->unified],
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or vice versa with \\[diff-unified->context] and you can also reverse the direction of
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a diff with \\[diff-reverse-direction].
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   \\{diff-mode-map}"