Re: highlight-changes-mode

[rsharman@pobox.com]

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Richard Stallman writes:
 >     I'm sure there's no good reason that it has to work the way it does.
 >     I think it just "seemed like a good idea at the time",  but as you say
 >     it isn't consistent with other modes.
 > 
 >     I can take a look into it in a couple of days.
 > 
 > That would be appreciated; thanks in advance.

I have made the changes so that command highlight-changes-mode simply
toggles the mode on and off, and so have introduced a new command
highlight-changes-toggle-visibility to toggle between what was
previously called active and passive modes.

At first I wasn't very happy with the changes, because now toggling
the main highlight changes mode loses information [the changes].
However, I now think it does seem a reasonable way of doing things.

A side effect of the new highlight-changes-toggle-visibility command
is that it enables highlight changes mode.  I was going to correct
this "bug" by making it only operate if the mode was active, but then
realized that the current behaviour is better.  People that wanted the
old method of one function to turn it on and toggle between active and
passive can basically just use the new command.

Attached is the new version;  please let me know what you think.

As well as the above change and some minor cleanup is a new command
highlight-compare-buffers that I think is occasionally useful.


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;;; hilit-chg.el --- minor mode displaying buffer changes with special face

;; Copyright (C) 1998, 2000, 2006 Free Software Foundation, Inc.
;; Author: Richard Sharman <rsharman@pobox.com>
;; Keywords: faces

;; 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
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; A minor mode: "Highlight Changes mode".

;; When Highlight Changes mode is enabled changes to the buffer are
;; recorded with a text property.  Normally these ranges of text are
;; displayed in a distinctive face.  However, sometimes it is
;; desirable to temporarily not see these changes.  Rather than
;; disabling Highlight Changes mode (which removes the text property)
;; the command highlight-changes-toggle-visibility toggles the use of
;; distinctive face for the changed text ranges.

;; Two faces are supported: one for changed or inserted text and
;; another for the first character after text has been deleted.

;; When Highlight Changes mode is on (even if changes are not visible) 
;; you can go to the next or previous change with
;; `highlight-changes-next-change' or `highlight-changes-previous-change'.

;; Command highlight-compare-with-file shows changes in this file
;; compared with another file (by default the previous version of the
;; file).  
;;
;; The command highlight-compare-buffers compares two buffers by
;; highlighting their differences.

;; You can "age" different sets of changes by using
;; `highlight-changes-rotate-faces'.  This rotates through a series
;; of different faces, so you can distinguish "new" changes from "older"
;; changes.  You can customize these "rotated" faces in two ways.  You can
;; either explicitly define each face by customizing
;; `highlight-changes-face-list'.  If, however, the faces differ from
;; `highlight-changes-face' only in the foreground color, you can simply set
;; `highlight-changes-colours'.  If `highlight-changes-face-list' is nil when
;; the faces are required they will be constructed from
;; `highlight-changes-colours'.

;; You can automatically rotate faces when the buffer is saved;
;; see function `highlight-changes-rotate-faces' for how to do this.

;; There are currently two hooks run by `highlight-changes-mode':
;; `highlight-changes-enable-hook'  - is run when Highlight Changes mode
;;				    is initially enabled for a buffer.
;; `highlight-changes-disable-hook' - is run when Highlight Changes mode

;; Example usage:
;; (defun my-highlight-changes-enable-hook ()
;;   (add-hook 'local-write-file-hooks 'highlight-changes-rotate-faces)
;; )
;;
;; (defun my-highlight-changes-disable-hook ()
;;   (remove-hook 'local-write-file-hooks 'highlight-changes-rotate-faces)
;; )
;;
;; (add-hook 'highlight-changes-enable-hook 'my-highlight-changes-enable-hook)
;; (add-hook 'highlight-changes-disable-hook
;;		'my-highlight-changes-disable-hook)



;;           Automatically enabling Highlight Changes mode


;; Normally, Highlight Changes mode is turned on explicitly in a buffer.

;; If you prefer to have it automatically invoked you can do it as
;; follows.

;; 1. Most modes have a major-hook, typically called MODE-hook.  You
;; can use `add-hook' to call `highlight-changes-mode'.

;;   Example:
;;	(add-hook 'c-mode-hook 'highlight-changes-mode)

;; However, this cannot be done for Fundamental mode for there is no
;; such hook.

;; 2. You can use the function `global-highlight-changes'

;; This function, which is fashioned after the way `global-font-lock' works,
;; toggles on or off global Highlight Changes mode.  When activated, it turns
;; on Highlight Changes mode in all "suitable" existing buffers and will turn
;; it on in new "suitable" buffers to be created.

;; A buffer's "suitability" is determined by variable
;; `highlight-changes-global-modes' as follows.  If this variable is
;; * nil  -- then no buffers are suitable;
;; * a function -- this function is called and the result is used.  As
;;   an example, if the value is `buffer-file-name' then all buffers
;;   who are visiting files are suitable, but others (like dired
;;   buffers) are not;
;; * a list -- then the buffer is suitable if and only if its mode is in the
;;   list, unless the first element is `not' in which case the test
;;   is reversed (i.e. it is a list of unsuitable modes).
;; * Otherwise, the buffer is suitable if its name does not begin with
;;   ` ' or `*' and if `buffer-file-name' returns true.

;; Normally toggling on or off Global Highlight Changes mode does not
;; change whether Highlight Changes mode is turned on or off for
;; existing buffers, but a user option can cause it to do so.

;; To enable it for future sessions put this in your ~/.emacs file:
;;		(global-highlight-changes t)


;;	Possible bindings:

;; (global-set-key '[C-right] 'highlight-changes-next-change)
;; (global-set-key '[C-left]  'highlight-changes-previous-change)
;;
;;     Other interactive functions (that could be bound if desired):
;; highlight-changes-mode
;; highlight-changes-toggle-visibility
;; highlight-changes-remove-highlight
;; highlight-compare-with-file
;; highlight-compare-buffers
;; highlight-changes-rotate-faces


;;; Bugs:

;; - the next-change and previous-change functions are too literal;
;;   they should find the next "real" change, in other words treat
;;   consecutive changes as one.


;;; To do (maybe), notes, ...

;; - having different faces for deletion and non-deletion: is it
;;   really worth the hassle?
;; - highlight-compare-with-file should allow RCS files - e.g. nice to be
;;   able to say show changes compared with version 2.1.


;;; History:

;; R Sharman (rsharman@pobox.com) Feb 1998:
;; - initial release as change-mode.
;; Jari Aalto <jari.aalto@ntc.nokia.com> Mar 1998
;; - fixes for byte compile errors
;; - use eval-and-compile for autoload
;; Marijn Ros <J.M.Ros@fys.ruu.nl> Mar 98
;; - suggested turning it on by default
;; Eric Ludlam <zappo@gnu.org> Suggested using overlays.
;; July 98
;; - global mode and various stuff added
;; - Changed to use overlays
;; August 98
;; - renamed to Highlight Changes mode.
;; Dec 2003
;; - Use require for ediff stuff to prevent problems with
;; highlight-compare-with-file when byte compiled in std directory
;; Nov 2006
;; - Made highlight-changes-mode like other modes (toggle on/off)
;; - Added new command highlight-changes-toggle-visibility to replace the
;;   previous active/passive aspect of highlight-changes-mode.
;; - Removed highlight-changes-toggle-hook
;; - Added highlight-compare-buffers

;;; Code:

(require 'wid-edit)

;; ====================== Customization =======================
(defgroup highlight-changes nil
  "Highlight Changes mode."
  :version "20.4"
  :group 'faces)


;; Face information: How the changes appear.

;; Defaults for face: red foreground, no change to background,
;; and underlined if a change is because of a deletion.
;; Note: underlining is helpful in that it shows up changes in white space.
;; However, having it set for non-delete changes can be annoying because all
;; indentation on inserts gets underlined (which can look pretty ugly!).

(defface highlight-changes-face
  '((((class color)) (:foreground "red" ))
    (t (:inverse-video t)))
  "Face used for highlighting changes."
  :group 'highlight-changes)

;; This looks pretty ugly, actually.  Maybe the underline should be removed.
(defface highlight-changes-delete-face
  '((((class color)) (:foreground "red" :underline t))
    (t (:inverse-video t)))
  "Face used for highlighting deletions."
  :group 'highlight-changes)



;; A (not very good) default list of colours to rotate through.
;;
(defcustom highlight-changes-colours
  (if (eq (frame-parameter nil 'background-mode) 'light)
      ;; defaults for light background:
      '( "magenta" "blue" "darkgreen" "chocolate" "sienna4" "NavyBlue")
      ;; defaults for dark background:
    '("yellow" "magenta" "blue" "maroon" "firebrick" "green4" "DarkOrchid"))
  "*Colours used by `highlight-changes-rotate-faces'.
The newest rotated change will be displayed in the first element of this list,
the next older will be in the second element etc.

This list is used if `highlight-changes-face-list' is nil, otherwise that
variable overrides this list.  If you only care about foreground
colours then use this, if you want fancier faces then set
`highlight-changes-face-list'."
  :type '(repeat color)
  :group 'highlight-changes)



;; highlight-changes-initial-state has been removed

;; highlight-changes-global-initial-state has been removed

;; The strings displayed in the mode-line for the minor mode:
(defcustom highlight-changes-active-string nil
  "*The string used when Highlight Changes mode and changes are visible.
This should be set to nil if no indication is desired, or to
a string with a leading space."
  :type '(choice string
		 (const :tag "None"  nil))
  :group 'highlight-changes)

(defcustom highlight-changes-passive-string " Chg"
  "*The string used when Highlight Changes mode but changes are not visible.
This should be set to nil if no indication is desired, or to
a string with a leading space."
  :type '(choice string
		 (const :tag "None"  nil))
  :group 'highlight-changes)

(defcustom highlight-changes-global-modes t
  "*Determine whether a buffer is suitable for global Highlight Changes mode.

A function means that function is called:  if it returns non-nil, the
buffer is suitable.

A list is a list of modes for which it is suitable, or a list whose
first element is `not' followed by modes which are not suitable.

t means the buffer is suitable if its name does not begin with ` ' nor
`*' and the buffer has a filename.

A value of nil means no buffers are suitable for
`global-highlight-changes-mode' (effectively disabling the mode).

Examples:
        (c-mode c++-mode)
means that Highlight Changes mode is turned on for buffers in C and C++
modes only."
  :type '(choice
	  (const :tag "all non-special buffers visiting files" t)
	  (set :menu-tag "specific modes" :tag "modes"
	       :value (not)
	       (const :tag "All except these" not)
	       (repeat :tag "Modes" :inline t (symbol :tag "mode")))
	  (function :menu-tag "determined by function"
			   :value buffer-file-name)
	  (const :tag "none" nil)
	  )
  :group 'highlight-changes)

(defvar global-highlight-changes nil)

(defcustom highlight-changes-global-changes-existing-buffers nil
  "*If non-nil, toggling global Highlight Changes mode affects existing buffers.
Normally, `global-highlight-changes' affects only new buffers (to be
created).  However, if `highlight-changes-global-changes-existing-buffers'
is non-nil, then turning on `global-highlight-changes' will turn on
Highlight Changes mode in suitable buffers, and turning the mode off will
remove it from existing buffers."
  :type 'boolean
  :group 'highlight-changes)

(defun hilit-chg-cust-fix-changes-face-list (w wc &optional event)
  ;; When customization function `highlight-changes-face-list' inserts a new
  ;; face it uses the default face.   We don't want the user to modify this
  ;; face, so we rename the faces in the list on an insert.  The rename is
  ;; actually done by copying the faces so user-defined faces still remain
  ;; in the same order.
  ;; The notifying the parent is needed because without it changes to the
  ;; faces are saved but not to the actual list itself.
  (let ((old-list (widget-value w)))
    (if (member 'default old-list)
	(let
	    ((p (reverse old-list))
	     (n (length old-list))
	     new-name old-name
	     (new-list nil)
	     )
	  (while p
	    (setq old-name (car p))
	    (setq new-name (intern (format "highlight-changes-face-%d" n)))
	    (if (eq old-name new-name)
		nil
	      ;; A new face has been inserted: we don't want to modify the
	      ;; default face so copy it.   Better, though, (I think) is to
	      ;; make a new face have the same attributes as
	      ;; highlight-changes-face .
	      (if (eq old-name 'default)
		  (copy-face 'highlight-changes-face  new-name)
		(copy-face old-name new-name)
		))
	    (setq new-list (append  (list new-name) new-list))
	    (setq n (1- n))
	    (setq p (cdr p)))
	  (if (equal new-list (widget-value w))
	      nil ;; (message "notify: no change!")
	    (widget-value-set w new-list)
	    (widget-setup)
	    )
	  )
      ;; (message "notify: no default here!")
      ))
  (let ((parent (widget-get w :parent)))
    (when parent
      (widget-apply parent :notify w event))))


(defcustom highlight-changes-face-list nil
  "*A list of faces used when rotating changes.
Normally the variable is initialized to nil and the list is created from
`highlight-changes-colours' when needed.  However, you can set this variable
to any list of faces.  You will have to do this if you want faces which
don't just differ from `highlight-changes-face' by the foreground colour.
Otherwise, this list will be constructed when needed from
`highlight-changes-colours'."
  :type '(choice
	  (repeat
	    :notify hilit-chg-cust-fix-changes-face-list
	    face  )
	  (const :tag "Derive from highlight-changes-colours"  nil)
	  )
  :group 'highlight-changes)

(defvar highlight-changes-visible-p t
  "*This controls the appearance of changes when Highlight Changes mode is on.
If non-nil, the changes are displayed using distinctive faces.

This variable is buffer-local when set.

Do not set this variable directly.  Instead,  use
\\[highlight-changes-toggle-visibility] to change this variable in a
buffer,  or use the Lisp function `setq-default' to change the default
value that is used for new buffers visited when Global Highlight Changes
mode is active.")

;; ========================================================================

;; These shouldn't be changed!

;; Autoload for the benefit of `make-mode-line-mouse-sensitive'.
;;;###autoload
(defvar highlight-changes-mode nil)

(defvar hilit-chg-list nil)
(defvar hilit-chg-string " ??")
(or (assq 'highlight-changes-mode minor-mode-alist)
    (setq minor-mode-alist
	  (cons '(highlight-changes-mode hilit-chg-string) minor-mode-alist)
	  ))
(make-variable-buffer-local 'highlight-changes-mode)
(make-variable-buffer-local 'highlight-changes-visible-p)
(make-variable-buffer-local 'hilit-chg-string)



;;; Functions...

(defun hilit-chg-map-changes  (func &optional start-position end-position)
  "Call function FUNC for each region used by Highlight Changes mode.
If START-POSITION is nil, (point-min) is used.
If END-POSITION is nil, (point-max) is used.
FUNC is called with 3 params: PROPERTY START STOP."
  (let ((start (or start-position (point-min)))
	(limit (or end-position (point-max)))
	prop end)
    (while (and start (< start limit))
      (setq prop (get-text-property start 'hilit-chg))
      (setq end (text-property-not-all start limit 'hilit-chg prop))
      (if prop
	  (funcall func prop start (or end limit)))
      (setq start end))))


(defun hilit-chg-display-changes (&optional beg end)
  "Display face information for Highlight Changes mode.

An overlay from BEG to END containing a change face is added from the
information in the text property of type `hilit-chg'.

This is the opposite of `hilit-chg-hide-changes'."
  (hilit-chg-map-changes 'hilit-chg-make-ov beg end))


(defun hilit-chg-make-ov (prop start end)
  ;; Put a highlight-changes overlay in the region.
  ;; PROP is the property type, either 'hilit-chg or 'hilit-chg-delete.\
  ;; The face used is determined from PROP.
  ;; the text property 'hilit-chg
  (let ((ov (make-overlay start end))
	face)
    (or prop
	(error "hilit-chg-make-ov: prop is nil"))
    (if (eq prop 'hilit-chg-delete)
	(setq face 'highlight-changes-delete-face)
      (setq face (nth 1 (member prop hilit-chg-list))))
    (if face
	(progn
	  ;; We must mark the face, that is the purpose of the overlay
	  (overlay-put ov 'face face)
	  ;; I don't think we need to set evaporate since we should
	  ;; be controlling them!
	  (overlay-put ov 'evaporate t)
	  ;; We set the change property so we can tell this is one
	  ;; of our overlays (so we don't delete someone else's).
	  (overlay-put ov 'hilit-chg t)
	  )
      (error "hilit-chg-make-ov: no face for prop: %s" prop))))

(defun hilit-chg-hide-changes (&optional beg end)
  "Remove face information for Highlight Changes mode.

The overlay containing the face is removed, but the text property
containing the change information is retained.

This is the opposite of `hilit-chg-display-changes'."
  (let ((start (or beg (point-min)))
	(limit (or end (point-max)))
	p)
    (setq p (overlays-in start limit))
    (while p
      ;; don't delete the overlay if it isn't ours!
      (if (overlay-get (car p) 'hilit-chg)
	  (delete-overlay (car p)))
      (setq p (cdr p)))))

(defun hilit-chg-fixup (beg end)
  "Fix change overlays in region between BEG and END.

Ensure the overlays agree with the changes as determined from
the text properties of type `hilit-chg' ."
  ;; Remove or alter overlays in region beg..end
  (let (p ov ov-start ov-end
	 props q)
    (setq p (overlays-in beg end))
    ;; temp for debugging:
    (unless (and highlight-changes-mode
		 highlight-changes-visible-p)
      ;; This can happen if the highlight-changes-mode variable was
      ;; manually set to nil without using the command 
      (error "hilit-chg-fixup called but Highlight Changes mode not active"))
    (while p
      (setq ov (car p))
      (setq ov-start (overlay-start ov))
      (setq ov-end (overlay-end ov))
      (if (< ov-start beg)
	  (progn
	    (move-overlay ov ov-start beg)
	    (if (> ov-end end)
		(progn
		  (setq props (overlay-properties ov))
		  (setq ov (make-overlay end ov-end))
		  (while props
		    (overlay-put ov (car props)(car (cdr props)))
		    (setq props (cdr (cdr props)))))))
	(if (> ov-end end)
	    (move-overlay ov end ov-end)
	  (delete-overlay ov)))
      (setq p (cdr p)))
    (hilit-chg-display-changes beg end)))

;;;###autoload
(defun highlight-changes-remove-highlight (beg end)
  "Remove the change face from the region between BEG and END.
This allows you to manually remove highlighting from uninteresting changes."
  (interactive "r")
  (let ((after-change-functions nil))
    (remove-text-properties beg end  '(hilit-chg nil))
    (hilit-chg-fixup beg end)))

(defun hilit-chg-set-face-on-change (beg end leng-before
	&optional no-proerty-change)
  "Record changes and optionally display them in a distinctive face.
`hilit-chg-set' adds this function to the `after-change-functions' hook."
  ;;
  ;; This function is called by the `after-change-functions' hook, which
  ;; is how we are notified when text is changed.
  ;; It is also called from `highlight-compare-with-file'.
  ;;
  ;; We do NOT want to simply do this if this is an undo command, because
  ;; otherwise an undone change shows up as changed.  While the properties
  ;; are automatically restored by undo, we must fix up the overlay.
  (save-match-data
    (let ((beg-decr 1) (end-incr 1)
	  (type 'hilit-chg)
	  old)
      (if undo-in-progress
	  (if (and highlight-changes-mode
		   highlight-changes-visible-p)
	      (hilit-chg-fixup beg end))
	(if (and (= beg end) (> leng-before 0))
	    ;; deletion
	    (progn
	      ;; The eolp and bolp tests are a kludge!  But they prevent
	      ;; rather nasty looking displays when deleting text at the end
	      ;; of line, such as normal corrections as one is typing and
	      ;; immediately makes a correction, and when deleting first
	      ;; character of a line.
;;;	      (if (= leng-before 1)
;;;		  (if (eolp)
;;;		      (setq beg-decr 0 end-incr 0)
;;;		    (if (bolp)
;;;			(setq beg-decr 0))))
;;;	      (setq beg (max (- beg beg-decr) (point-min)))
	      (setq end (min (+ end end-incr) (point-max)))
	      (setq type 'hilit-chg-delete))
	  ;; Not a deletion.
	  ;; Most of the time the following is not necessary, but
	  ;; if the current text was marked as a deletion then
	  ;; the old overlay is still in effect, so if we add some
	  ;; text then remove the deletion marking, but set it to
	  ;; changed otherwise its highlighting disappears.
	  (if (eq (get-text-property end 'hilit-chg) 'hilit-chg-delete)
	      (progn
		(remove-text-properties end (+ end 1) '(hilit-chg nil))
		(put-text-property end (+ end 1) 'hilit-chg 'hilit-chg)
		(if highlight-changes-visible-p
		    (hilit-chg-fixup beg (+ end 1))))))
	(unless no-proerty-change
		(put-text-property beg end 'hilit-chg type))
	(if (or highlight-changes-visible-p no-proerty-change)
	    (hilit-chg-make-ov type beg end))))))

(defun hilit-chg-set ()
  "Turn on Highlight Changes mode for this buffer."
  (remove-hook 'after-change-functions 'hilit-chg-set-face-on-change t)
  (hilit-chg-make-list)
  (setq highlight-changes-mode t)
  (if highlight-changes-visible-p
      (progn
	(setq hilit-chg-string highlight-changes-active-string)
	(or buffer-read-only
	    (hilit-chg-display-changes)))
    ;; changes are invisible
    (setq hilit-chg-string highlight-changes-passive-string)
    (or buffer-read-only
	(hilit-chg-hide-changes)))
  (force-mode-line-update)
  (make-local-hook 'after-change-functions)
  (add-hook 'after-change-functions 'hilit-chg-set-face-on-change nil t)
  (run-hooks 'highlight-changes-enable-hook)
  )

(defun hilit-chg-clear ()
  "Remove Highlight Changes mode for this buffer.
This removes all saved change information."
  (if buffer-read-only
      ;; We print the buffer name because this function could be called
      ;; on many buffers from `global-highlight-changes'.
      (message "Cannot remove highlighting from read-only mode buffer %s"
	       (buffer-name))
    (remove-hook 'after-change-functions 'hilit-chg-set-face-on-change t)
    (let ((after-change-functions nil))
      (hilit-chg-hide-changes)
      (hilit-chg-map-changes
       '(lambda (prop start stop)
	  (remove-text-properties start stop '(hilit-chg nil))))
      )
    (setq highlight-changes-mode nil)
    (force-mode-line-update)
    ;; If we type:  C-u -1 M-x highlight-changes-mode
    ;; we want to turn it off, but hilit-chg-post-command-hook
    ;; runs and that turns it back on!
    (remove-hook 'post-command-hook 'hilit-chg-post-command-hook))
  (run-hooks 'highlight-changes-disable-hook)
  )

;;;###autoload
(defun highlight-changes-mode (&optional arg)
  "Toggle Highlight Changes mode.

With ARG, turn Highlight Changes mode on if and only if arg is positive.

In Highlight Changes mode changes are recorded with a text property.
Normally they are displayed in a distinctive face, but command
\\[highlight-changes-toggle-visibility] can be used to toggles this
on and off.

Other functions for buffers in this mode include:
\\[highlight-changes-next-change] - move point to beginning of next change
\\[highlight-changes-previous-change] - move to beginning of previous change
\\[highlight-changes-remove-highlight] - remove the change face from the region
\\[highlight-changes-rotate-faces] - rotate different \"ages\" of changes
through	various faces.
\\[highlight-compare-with-file] - mark text as changed by comparing this
buffer with the contents of a file
\\[highlight-compare-buffers] highlights differences between two buffers.

Hook variables:
`highlight-changes-enable-hook'  - called when enabling Highlight Changes mode.
`highlight-changes-disable-hook' - called when disabling off Highlight Changes mode."
  (interactive "P")
  (if (or (display-color-p)
	  (and (fboundp 'x-display-grayscale-p) (x-display-grayscale-p)))
      (let ((was-on highlight-changes-mode))
	(setq highlight-changes-mode
	      (if (null arg)
		  (not highlight-changes-mode)
		(> (prefix-numeric-value arg) 0)))
	(if (eq was-on highlight-changes-mode)
	    (message "highlight-changes-mode - already %s"
		     (if highlight-changes-mode "on" "off"))
	  (message "highlight-changes-mode is now %s"
		   (if highlight-changes-mode "on" "off"))
	  (if highlight-changes-mode
	      ;; it is being turned on
	      ;; the hook has been moved into hilit-chg-set
	      ;; (run-hooks 'highlight-changes-enable-hook))
	      (hilit-chg-set)
	    ;; mode is turned off
	  (hilit-chg-clear))))
    (message "Highlight Changes mode requires color or grayscale display")))

;;;###autoload
(defun highlight-changes-next-change ()
  "Move to the beginning of the next change, if in Highlight Changes mode."
  (interactive)
  (if highlight-changes-mode
      (let ((start (point))
	    prop)
	(setq prop (get-text-property (point) 'hilit-chg))
	(if prop
	    ;; we are in a change
	    (setq start (next-single-property-change (point) 'hilit-chg)))
	(if start
	    (setq start (next-single-property-change start 'hilit-chg)))
	(if start
	    (goto-char start)
	  (message "no next change")))
    (message "This buffer is not in Highlight Changes mode.")))


;;;###autoload
(defun highlight-changes-previous-change ()
  "Move to the beginning of the previous change, if in Highlight Changes mode."
  (interactive)
  (if highlight-changes-mode
      (let ( (start (point)) (prop nil) )
	(or (bobp)
	    (setq prop (get-text-property (1- (point)) 'hilit-chg)))
	(if prop
	    ;; we are in a change
	    (setq start (previous-single-property-change (point) 'hilit-chg)))
	(if start
	    (setq start (previous-single-property-change start 'hilit-chg)))
	;; special handling for the case where (point-min) is a change
	(if start
	    (setq start (or (previous-single-property-change start 'hilit-chg)
			    (if (get-text-property (point-min) 'hilit-chg)
				(point-min)))))
	(if start
	    (goto-char start)
	  (message "no previous change")))
    (message "This buffer is not in Highlight Changes mode.")))


;;;###autoload
(defun highlight-changes-toggle-visibility (&optional arg)
  "Toggle whether changes are visible in Highlight Changes modes.
While the changes are still kept (and new ones recorded) as long as
Highlight Changes modes is on, their distinctive display can be
toggled on and off using this command.  With ARG,  enable the
distinctive display if and only if the arg is positive.

Set variable `highlight-changes-visible-p' if you want to change the default
behaviour.

This command turns on highlight-changes mode."
  (interactive "P")
  (let ((old-value highlight-changes-visible-p))
    (setq highlight-changes-visible-p
	  (if (null arg)
	      (not highlight-changes-visible-p)
	    (> (prefix-numeric-value arg) 0)))
    (unless (eq old-value highlight-changes-visible-p)
      (message "changes will now be %s"
	       (if highlight-changes-visible-p "visible" "invisible"))
      (hilit-chg-set))
    ))
	  
      
;; ========================================================================

(defun hilit-chg-make-list (&optional force)
  "Construct `hilit-chg-list' and `highlight-changes-face-list'."
  ;; Constructs highlight-changes-face-list if necessary,
  ;; and hilit-chg-list always:
  ;; Maybe this should always be called when rotating a face
  ;; so we pick up any changes?
  (if (or (null highlight-changes-face-list)  ; Don't do it if it
	  force) ; already exists unless FORCE non-nil.
      (let ((p highlight-changes-colours)
	    (n 1) name)
	(setq highlight-changes-face-list nil)
	(while p
	  (setq name (intern (format "highlight-changes-face-%d" n)))
	  (copy-face 'highlight-changes-face name)
	  (set-face-foreground name (car p))
	  (setq highlight-changes-face-list
		(append highlight-changes-face-list (list name)))
	  (setq p (cdr p))
	  (setq n (1+ n)))))
  (setq hilit-chg-list (list 'hilit-chg 'highlight-changes-face))
  (let ((p highlight-changes-face-list)
	(n 1)
	last-category last-face)
    (while p
      (setq last-category (intern (format "change-%d" n)))
      ;; (setq last-face (intern (format "highlight-changes-face-%d" n)))
      (setq last-face (car p))
      (setq hilit-chg-list
	    (append hilit-chg-list
		    (list last-category last-face)))
      (setq p (cdr p))
      (setq n (1+ n)))
    (setq hilit-chg-list
	  (append hilit-chg-list
		  (list last-category last-face)))))

(defun hilit-chg-bump-change (prop start end)
  "Increment (age) the Highlight Changes mode text property."
  (let ( new-prop )
    (if (eq prop 'hilit-chg-delete)
	(setq new-prop (nth 2 hilit-chg-list))
      (setq new-prop (nth 2 (member prop hilit-chg-list))))
    (if prop
	(put-text-property start end 'hilit-chg new-prop)
      (message "%d-%d unknown property %s not changed" start end prop))))

;;;###autoload
(defun highlight-changes-rotate-faces ()
  "Rotate the faces used by Highlight Changes mode.

Current changes are displayed in the face described by the first element
of `highlight-changes-face-list', one level older changes are shown in
face described by the second element, and so on.  Very old changes remain
shown in the last face in the list.

You can automatically rotate colours when the buffer is saved
by adding the following to `local-write-file-hooks', by evaling it in the
buffer to be saved):

  \(add-hook 'local-write-file-hooks 'highlight-changes-rotate-faces)"
  (interactive)
  ;; If not in active mode do nothing but don't complain because this
  ;; may be bound to a hook.
  (if (and highlight-changes-mode
	   highlight-changes-visible-p)
      (let ((after-change-functions nil))
	;; ensure hilit-chg-list is made and up to date
	(hilit-chg-make-list)
	;; remove our existing overlays
	(hilit-chg-hide-changes)
	;; for each change text property, increment it
	(hilit-chg-map-changes 'hilit-chg-bump-change)
	;; and display them all if visible
	(if highlight-changes-visible-p
	    (hilit-chg-display-changes))))
  ;; This always returns nil so it is safe to use in
  ;; local-write-file-hook
  nil)

;; ========================================================================
;; Comparing buffers/files
;; These use ediff to find the differences.

(defun highlight-markup-buffers
  (buf-a file-a buf-b file-b &optional markup-a-only)
  "Get differences between two buffers and set highlight changes.
Both buffers are done unless optional parameter MARKUP-A-ONLY
is non-nil."
  (require 'ediff-util)
  (save-window-excursion
    (let* (change-info
	   change-a change-b
	   a-start a-end len-a
	   b-start b-end len-b
	   (bufa-modified (buffer-modified-p buf-a))
	   (bufb-modified (buffer-modified-p buf-b))
	   (buf-a-read-only (with-current-buffer buf-a buffer-read-only))
	   (buf-b-read-only (with-current-buffer buf-b buffer-read-only))
	   temp-a temp-b)
      (if (and file-a bufa-modified)
	  (if (y-or-n-p (format "Save buffer %s?  " buf-a))
	      (with-current-buffer buf-a
		(save-buffer)
		(setq bufa-modified (buffer-modified-p buf-a)))
	    (setq file-a nil)))
      (or file-a
	  (setq temp-a (setq file-a (ediff-make-temp-file buf-a nil))))

      (if (and file-b bufb-modified)
	  (if (y-or-n-p (format "Save buffer %s?  " buf-b))
	      (with-current-buffer buf-b
		(save-buffer)
		(setq bufb-modified (buffer-modified-p buf-b)))
	    (setq file-b nil)))
      (or file-b
	  (setq temp-b (setq file-b (ediff-make-temp-file buf-b nil))))
      (set-buffer buf-a)
      (highlight-changes-mode 'active)
      (or markup-a-only (with-current-buffer buf-b
			  (highlight-changes-mode 'active)))
      (setq change-info (hilit-chg-get-diff-info buf-a file-a buf-b file-b))


      (setq change-a (car change-info))
      (setq change-b (car (cdr change-info)))
      
      (hilit-chg-make-list)
      (while change-a
	(setq a-start (nth 0 (car change-a)))
	(setq a-end (nth 1 (car change-a)))
	(setq b-start (nth 0 (car change-b)))
	(setq b-end (nth 1 (car change-b)))
	(setq len-a (- a-end a-start))
	(setq len-b (- b-end b-start))
	(set-buffer buf-a)
	(hilit-chg-set-face-on-change a-start a-end len-b buf-a-read-only)
	(or markup-a-only
	    (with-current-buffer buf-b
	      (hilit-chg-set-face-on-change b-start b-end len-a
					    buf-b-read-only)
	      ))
	(setq change-a (cdr change-a))
	(setq change-b (cdr change-b)))
      (or bufa-modified
	  (with-current-buffer buf-a (set-buffer-modified-p nil)))
      (or bufb-modified
	  (with-current-buffer buf-b (set-buffer-modified-p nil)))
      (if temp-a
	  (delete-file temp-a))
      (if temp-b
	  (delete-file temp-b)))
    ))

;;;###autoload
(defun highlight-compare-buffers (buf-a buf-b)
"Compare two buffers and highlight the differences.

The default is the current buffer and the one in the next window.

If either buffer is modified and is visiting a file, you are prompted
to save the file.

Unless the buffer is unmodified and visiting a file,  the buffer is
written to a temporary file for comparison.

If a buffer is read-only, differences will be highlighted but no property
changes are made, so \\[highlight-changes-next-change] and
\\[highlight-changes-previous-change] will not work."
  (interactive
   (list
    (get-buffer (read-buffer "buffer-a " (current-buffer) t))
    (get-buffer
     (read-buffer "buffer-b "
		  (window-buffer (next-window (selected-window))) t))))
  (let ((file-a (buffer-file-name buf-a))
	(file-b (buffer-file-name buf-b)))
    (highlight-markup-buffers buf-a file-a buf-b file-b)
    ))

;;;###autoload
(defun highlight-compare-with-file (file-b)
  "Compare this buffer with a file, and highlight differences.

If the buffer has a backup filename, it is used as the default when
this function is called interactively.

If the current buffer is visiting the file being compared against, it
also will have its differences highlighted.  Otherwise, the file is
read in temporarily but the buffer is deleted.

If the buffer is read-only, differences will be highlighted but no property
changes are made, so \\[highlight-changes-next-change] and
\\[highlight-changes-previous-change] will not work."
  (interactive (list
	      (read-file-name
	       "File to compare with? " ;; prompt
	       ""			;; directory
	       nil			;; default
	       'yes			;; must exist
	       (let ((f (buffer-file-name (current-buffer)))) ;; initial
		 (if f
		     (progn
		       (setq f (make-backup-file-name f))
		       (or (file-exists-p f)
			   (setq f nil))))
		 f))))
  (let* ((buf-a (current-buffer))
	 (file-a (buffer-file-name))
	 (existing-buf (get-file-buffer file-b))
	 (buf-b (or existing-buf
		    (find-file-noselect file-b)))
	 (buf-b-read-only (with-current-buffer buf-b buffer-read-only)))
    (highlight-markup-buffers buf-a file-a buf-b file-b (not existing-buf))
    (unless existing-buf
      (kill-buffer buf-b))
    ))


(defun hilit-chg-get-diff-info (buf-a file-a buf-b file-b)
  (let ((e nil) x y)   ;; e is set by function hilit-chg-get-diff-list-hk
    (ediff-setup buf-a file-a buf-b file-b
	       nil nil   ; buf-c file-C
	       'hilit-chg-get-diff-list-hk
	       (list (cons 'ediff-job-name 'something))
	       )
    (ediff-with-current-buffer e (ediff-really-quit nil))
    (list x y)))


(defun hilit-chg-get-diff-list-hk ()
  ;; x and y are dynamically bound by hilit-chg-get-diff-info
  ;; which calls this function as a hook
  (defvar x)  ;; placate the byte-compiler
  (defvar y)
  (setq  e (current-buffer))
  (let ((n 0) extent p va vb a b)
    (setq  x nil  y nil)    ;; x and y are bound by hilit-chg-get-diff-info
    (while (< n ediff-number-of-differences)
      (ediff-make-fine-diffs n)
      (setq va (ediff-get-fine-diff-vector n 'A))
      ;; va is a vector if there are fine differences
      (if va
	  (setq a (append va nil))
	;; if not, get the unrefined difference
	(setq va (ediff-get-difference n 'A))
	(setq a (list (elt va 0))))
      ;; a list a list
      (setq p a)
      (while p
	(setq extent (list (overlay-start (car p))
			   (overlay-end (car p))))
	(setq p (cdr p))
	(setq x (append x (list extent) )));; while p
      ;;
      (setq vb (ediff-get-fine-diff-vector n 'B))
      ;; vb is a vector
      (if vb
	  (setq b (append vb nil))
	;; if not, get the unrefined difference
	(setq vb (ediff-get-difference n 'B))
	(setq b (list (elt vb 0))))
      ;; b list a list
      (setq p b)
      (while p
	(setq extent (list (overlay-start (car p))
			   (overlay-end (car p))))
	(setq p (cdr p))
	(setq y (append y (list extent) )))
      (setq n (1+ n)));; while
    ;; ediff-quit doesn't work here.
    ;; No point in returning a value, since this is a hook function.
    ))

;; ======================= automatic stuff ==============

;; Global Highlight Changes mode is modeled after Global Font-lock mode.
;; Three hooks are used to gain control.  When Global Changes Mode is
;; enabled, `find-file-hooks' and `change-major-mode-hook' are set.
;; `find-file-hooks' is called when visiting a file, the new mode is
;; known at this time.
;; `change-major-mode-hook' is called when a buffer is changing mode.
;; This could be because of finding a file in which case
;; `find-file-hooks' has already been called and has done its work.
;; However, it also catches the case where a new mode is being set by
;; the user.  However, it is called from `kill-all-variables' and at
;; this time the mode is the old mode, which is not what we want.
;; So, our function temporarily sets `post-command-hook' which will
;; be called after the buffer has been completely set up (with the new
;; mode).  It then removes the `post-command-hook'.
;; One other wrinkle - every M-x command runs the `change-major-mode-hook'
;; so we ignore this by examining the buffer name.


(defun hilit-chg-major-mode-hook ()
  (add-hook 'post-command-hook 'hilit-chg-post-command-hook))

(defun hilit-chg-post-command-hook ()
  ;; This is called after changing a major mode, but also after each
  ;; M-x command, in which case the current buffer is a minibuffer.
  ;; In that case, do not act on it here, but don't turn it off
  ;; either, we will get called here again soon-after.
  ;; Also, don't enable it for other special buffers.
  (if (string-match "^[ *]"  (buffer-name))
      nil ;; (message "ignoring this post-command-hook")
    (remove-hook 'post-command-hook 'hilit-chg-post-command-hook)
    ;; The following check isn't necessary, since
    ;; hilit-chg-turn-on-maybe makes this check too.
    (or highlight-changes-mode	;; don't turn it on if it already is
	(hilit-chg-turn-on-maybe))))

(defun hilit-chg-check-global ()
  ;; This is called from the find file hook.
  (hilit-chg-turn-on-maybe))


;;;###autoload
(defun global-highlight-changes (&optional arg)
  "Turn on or off Global Highlight Changes mode.
With ARG, turn Global Highlight Changes mode on if and only if arg is positive.
When global Highlight Changes mode is enabled, Highlight Changes mode is turned
on for future \"suitable\" buffers (and for \"suitable\" existing buffers if
variable `highlight-changes-global-changes-existing-buffers' is non-nil).
\"Suitability\" is determined by variable `highlight-changes-global-modes'."
  (interactive "P")
  (setq global-highlight-changes
	(if (null arg)
	    (not global-highlight-changes)
	  (> (prefix-numeric-value arg) 0)))
  (if global-highlight-changes
      (progn
	(message "Turning ON Global Highlight Changes mode")
	(add-hook 'hilit-chg-major-mode-hook 'hilit-chg-major-mode-hook)
	(add-hook 'find-file-hooks 'hilit-chg-check-global)
	(if highlight-changes-global-changes-existing-buffers
	    (hilit-chg-update-all-buffers t)))
    (message "Turning OFF global Highlight Changes mode")
    (remove-hook 'hilit-chg-major-mode-hook 'hilit-chg-major-mode-hook)
    (remove-hook 'find-file-hooks 'hilit-chg-check-global)
    (remove-hook 'post-command-hook
		 'hilit-chg-post-command-hook)
    (remove-hook 'find-file-hooks 'hilit-chg-check-global)
    (if highlight-changes-global-changes-existing-buffers
	(hilit-chg-update-all-buffers nil))))


(defun hilit-chg-turn-on-maybe ()
  "Turn on Highlight Changes mode if it is appropriate for this buffer.

A buffer is appropriate for Highlight Changes mode if all these are true:
- the buffer is not a special buffer (one whose name begins with
  `*' or ` ')
- the buffer's mode is suitable as per variable
  `highlight-changes-global-modes'
- Highlight Changes mode is not already on for this buffer.

This function is called from `hilit-chg-update-all-buffers' or
from `global-highlight-changes' when turning on global Highlight Changes mode."
  (or highlight-changes-mode			; do nothing if already on
      (if
	  (cond
	   ((null highlight-changes-global-modes)
	    nil)
	   ((functionp highlight-changes-global-modes)
	    (funcall highlight-changes-global-modes))
	    ((listp highlight-changes-global-modes)
	     (if (eq (car-safe highlight-changes-global-modes) 'not)
		 (not (memq major-mode (cdr highlight-changes-global-modes)))
	       (memq major-mode highlight-changes-global-modes)))
	    (t
	     (and
	      (not (string-match "^[ *]"  (buffer-name)))
	      (buffer-file-name))))
	  (progn
	    (hilit-chg-set))
	)))


(defun hilit-chg-turn-off-maybe ()
  (if highlight-changes-mode
      (hilit-chg-clear)))


(defun hilit-chg-update-all-buffers (value)
  (mapcar
   (function (lambda (buffer)
	       (with-current-buffer buffer
		 (if value
		     (hilit-chg-turn-on-maybe)
		   (hilit-chg-turn-off-maybe))
		 )))
   (buffer-list)))

;; ===================== debug ==================
;; For debug & test use:
;;
;; (defun hilit-chg-debug-show (&optional beg end)
;;   (interactive)
;;   (message "--- hilit-chg-debug-show ---")
;;   (hilit-chg-map-changes '(lambda (prop start end)
;; 			      (message "%d-%d: %s" start end prop)
;; 			      )
;; 			   beg end
;; 			   ))
;;
;; ================== end of debug ===============

(provide 'hilit-chg)

;;; hilit-chg.el ends here

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Richard

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