emacs/lisp/hilit-chg.el

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

;; Copyright (C) 1998 Free Software Foundation, Inc.

;; Author: Richard Sharman <rsharman@pobox.com>
;; Keywords: faces

;; This file is part of GNU Emacs.

;; This program 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.

;; This program 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".
;;

;; Highlight Changes mode has 2 submodes: active and passive.
;; When active, changes to the buffer are displayed in a different face.
;; When passive, any existing displayed changes are saved and new ones
;; recorded but are not displayed differently.
;; Why active and passive?  Having the changes visible can be handy when you
;; want the information but very distracting otherwise.  So, you can keep
;; Highlight Changes mode in passive state while you make your changes, toggle
;; it on to active mode to see them, then toggle it back off to avoid
;; distraction.
;; 
;; When active, changes are displayed in `highlight-changes-face'.  When
;; text is deleted,  the following character is displayed in
;; `highlight-changes-delete-face' face.
;;
;;
;; You can "age" different sets of changes by using
;; `highlight-changes-rotate-faces'.  This rotates different 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 colour, 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'.
;;
;;
;; When a Highlight Changes mode is on (either active or passive) you can go
;; to the next or previous change with `highlight-changes-next-change' and
;; `highlight-changes-previous-change'.
;;
;;
;; You can also use the command highlight-compare-with-file to show changes
;; in this file compared with another file (typically the previous version
;; of the file).
;;
;;
;; There are currently three 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
;;				    is turned off.
;; `highlight-changes-toggle-hook'  - is run each time `highlight-changes-mode'
;;				    is called.  Typically this is when
;;				    toggling between active and passive
;;				    modes.  The variable
;;				    `highlight-changes-mode' contains the new
;;				    state (`active' or `passive'.)
;;				    
;;
;; 
;; 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)


;;           Explciit vs. Implicit
;;

;; 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)
;;
;;  If you want to make it start up in passive mode (regardless of the
;;  setting of highlight-changes-initial-state):
;;      (add-hook 'emacs-lisp-mode-hook 
;; 	    (lambda ()
;; 	      (highlight-changes-mode 'passive)))
;;
;; 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" existings 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 the 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 if the buufer is suitable iff its mode is in the
;;   list,  exccept if the first element is nil 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.
;;



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

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


;;; 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?
;; - should have better hooks:  when should they be run?
;; - highlight-compare-with-file should allow RCS files - e.g. nice to be
;;   able to say show changes compared with version 2.1.
;; - Maybe we should have compare-with-buffer as well.  (When I tried
;;   a while back I ran into a problem with ediff-buffers-internal.)


;;; History:

;; R Sharman (rsharman@magma.ca) 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
;; - renmaed to Highlight Changes mode.


;;; 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 is 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
  )
 

;; If you invoke highlight-changes-mode with no argument,  should it start in
;; active or passive mode?
;;
(defcustom highlight-changes-initial-state 'active
  "*What state (active or passive) `highlight-changes' should start in.
This is used when `highlight-changes' is called with no argument.
This variable must be set to one of the symbols `active' or `passive'."
  :type '(choice (const :tag "Active" active)
		 (const :tag "Passive" passive))
  :group 'highlight-changes
  )

(defcustom highlight-changes-global-initial-state 'passive
  "*What state `global-highlight-changes' should start in.
This is used if `global-highlight-changes' is called with no argument.
This variable must be set to either `active' or `passive'"
  :type '(choice (const :tag "Active" active)
		 (const :tag "Passive" passive))
  :group 'highlight-changes
  )

;; The strings displayed in the mode-line for the minor mode:
(defcustom highlight-changes-active-string nil
  "*The string used when Highlight Changes mode is in the active state.
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 is in the passive state.
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.

nil means no buffers are suitable for `global-highlight-changes'
(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' means 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 rotatating 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
  )

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

;; 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 'hilit-chg-string)



(eval-and-compile
  ;;  For highlight-compare-with-file
  (defvar ediff-number-of-differences)
  (autoload 'ediff-setup		"ediff")
  (autoload 'ediff-with-current-buffer	"ediff")
  (autoload 'ediff-really-quit		"ediff")
  (autoload 'ediff-make-fine-diffs	"ediff")
  (autoload 'ediff-get-fine-diff-vector "ediff")
  (autoload 'ediff-get-difference	"ediff")
  )



;;; 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 containing a change face is added,  from the information
in the text property of type change.

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)
  ;; for the region make change overlays corresponding to
  ;; 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 ov)
    (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 beg .. 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:
    ;; (or (eq highlight-changes-mode 'active)
    ;;	 (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.  
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 fixup the overlay.
  (save-match-data
    (let ((beg-decr 1) (end-incr 1)
	  (type 'hilit-chg)
	  old)
      (if undo-in-progress
	  (if (eq highlight-changes-mode 'active)
	      (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 corrections,  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 (eq highlight-changes-mode 'active)
		    (hilit-chg-fixup beg (+ end 1))))))
	(unless no-proerty-change
		(put-text-property beg end 'hilit-chg type))
	(if (or (eq highlight-changes-mode 'active) no-proerty-change)
	    (hilit-chg-make-ov type beg end))
	))))





(defun hilit-chg-set (value)
  "Turn on Highlight Changes mode for this buffer."
  (setq highlight-changes-mode value)
  (remove-hook 'after-change-functions 'hilit-chg-set-face-on-change t)
  (hilit-chg-make-list)
  (if (eq highlight-changes-mode 'active)
      (progn
	(setq hilit-chg-string highlight-changes-active-string)
	(or buffer-read-only
	    (hilit-chg-display-changes)))
    ;; mode is passive
    (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)
  )

(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)
    ))

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

Without an argument,  
  if Highlight Changes mode is not enabled, then enable it (to either active
  or passive as determined by variable highlight-changes-initial-state);
  otherwise, toggle between active and passive states.

With an argument,
  if just C-u  or  a positive argument,  set state to active;
  with a zero argument,  set state to passive;
  with a negative argument,  disable Highlight Changes mode completely.

Active state -  means changes are shown in a distinctive face.
Passive state - means changes are kept and new ones recorded but are
		not displayed in a different face.

Functions:
\\[highlight-changes-next-change] - move point to beginning of next change
\\[highlight-changes-previous-change] - move to beginning of previous change 
\\[highlight-compare-with-file] - mark text as changed by comparing this
	buffer with the contents of a file
\\[highlight-changes-remove-highlight] - remove the change face from the region
\\[highlight-changes-rotate-faces] - rotate different \"ages\" of changes \
through 
	various faces.


Hook variables:
highlight-changes-enable-hook - when Highlight Changes mode enabled.
highlight-changes-toggle-hook - when entering active or passive state
highlight-changes-disable-hook - when turning off Highlight Changes mode.
"
  (interactive "P")
  (if window-system
      (let ((was-on highlight-changes-mode)
	    (new-highlight-changes-mode
	     (cond
	      ((null arg)
	       ;; no arg => toggle (or set to active initially)
	       (if highlight-changes-mode
		   (if (eq highlight-changes-mode 'active) 'passive 'active)
		 highlight-changes-initial-state))
	      ;; an argument is given
	      ((eq arg 'active)
	       'active)
	      ((eq arg  'passive)
	       'passive)
	      ((> (prefix-numeric-value arg) 0)
	       'active)
	      ((< (prefix-numeric-value arg) 0)
	       nil)
	      (t
	       'passive)
	      )))
	(if new-highlight-changes-mode
	    ;; mode is turned on -- but may be passive
	    (progn
	      (hilit-chg-set new-highlight-changes-mode)
	      (or was-on
		  ;; run highlight-changes-enable-hook once
		  (run-hooks 'highlight-changes-enable-hook))
	      (run-hooks 'highlight-changes-toggle-hook))
	  ;; mode is turned off
	  (run-hooks 'highlight-changes-disable-hook)
	  (hilit-chg-clear))
	)
    (message "Highlight Changes mode only works when using a window system"))
  )



;;;###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.")))


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


(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 of type change."
  (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 will be display in the face described by the first element
of highlight-changes-face-list, those (older) changes will be shown in the
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 this to local-write-file-hooks,  by evaling (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 (eq highlight-changes-mode 'active)
      (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 active
	(if (eq highlight-changes-mode 'active)
	    (hilit-chg-display-changes))
	))
  ;; This always returns nil so it is safe to use in
  ;; local-write-file-hook
  nil)


;; ========================================================================
;; Comparing with an existing file.   
;; This uses ediff to find the differences.

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

The current buffer must be an unmodified buffer visiting a file,
and not in read-only mode.

If the backup filename exists, it is used as the default
when called interactively.

If a 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 a buffer is read-only,  differences will be highlighted but no property
changes 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 (make-backup-file-name 
			 (or (buffer-file-name (current-buffer))
			     (error "no file for this buffer")))))
		 (if (file-exists-p f) f ""))
	       )))

  (let* ((buf-a (current-buffer))
	 (buf-a-read-only buffer-read-only)
	 (orig-pos (point))
	 (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))
	 xy  xx yy p q
	 a-start a-end len-a
	 b-start b-end len-b
	 )

    ;; We use the fact that the buffer is not marked modified at the
    ;; end where we clear its modified status
    (if (buffer-modified-p buf-a)
	(if (y-or-n-p (format "OK to save %s?  " file-a))
		       (save-buffer buf-a)
	  (error "Buffer must be saved before comparing with a file.")))
    (if (and existing-buf (buffer-modified-p buf-b))
	(if (y-or-n-p (format "OK to save %s?  " file-b))
		       (save-buffer buf-b)
	  (error "Cannot compare with a file in an unsaved buffer.")))
    (highlight-changes-mode 'active)
    (if existing-buf (with-current-buffer buf-b
		       (highlight-changes-mode 'active)))
    (save-window-excursion
      (setq xy (hilit-chg-get-diff-info buf-a file-a buf-b file-b)))
    (setq xx (car xy))
    (setq p xx)
    (setq yy (car (cdr xy)))
    (setq q yy)
    (hilit-chg-make-list)
    (while p
      (setq a-start (nth 0 (car p)))
      (setq a-end (nth 1 (car p)))
      (setq b-start (nth 0 (car q)))
      (setq b-end (nth 1 (car q)))
      (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)
      (set-buffer-modified-p nil)
      (goto-char orig-pos)
      (if existing-buf
	  (with-current-buffer buf-b
	    (hilit-chg-set-face-on-change b-start b-end len-a
					  buf-b-read-only )
	    ))
      (setq p (cdr p))
      (setq q (cdr q))
      )
    (if existing-buf
	(set-buffer-modified-p nil) 
      (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) ))
	);; while p
      ;;
      (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 modelled 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 highlight-changes-global-initial-state))
    ))

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



;;;###autoload
(defun global-highlight-changes (&optional arg)
  "Turn on or off global Highlight Changes mode.

When called interactively:
- if no prefix, toggle global Highlight Changes mode on or off
- if called with a positive prefix (or just C-u) turn it on in active mode
- if called with a zero prefix  turn it on in passive mode
- if called with a negative prefix turn it off

When called from a program:
- if ARG is nil or omitted, turn it off
- if ARG is 'active,  turn it on in active mode
- if ARG is 'passive, turn it on in passive mode
- otherwise just turn it on 

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).
\"Suitablity\" is determined by variable `highlight-changes-global-modes'."

  (interactive 
   (list
    (cond
     ((null current-prefix-arg)
      ;; no arg => toggle it on/off
      (setq global-highlight-changes (not global-highlight-changes)))
     ;; positive interactive arg - turn it on as active
     ((> (prefix-numeric-value current-prefix-arg) 0)
      (setq global-highlight-changes t)
      'active)
     ;; zero interactive arg - turn it on as passive
     ((= (prefix-numeric-value current-prefix-arg) 0)
      (setq global-highlight-changes t)
      'passive)
     ;; negative interactive arg - turn it off
     (t
      (setq global-highlight-changes nil)      
      nil))))

  (if arg
      (progn
	(if (eq arg 'active)
	    (setq highlight-changes-global-initial-state 'active)
	  (if (eq arg  'passive)
	      (setq highlight-changes-global-initial-state 'passive)))
	(setq global-highlight-changes t)
	(message "turning ON Global Highlight Changes mode in %s state"
		 highlight-changes-global-initial-state)
	(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 
	     highlight-changes-global-initial-state))
	)
    (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 (value)
  "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 
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 value)
	    (run-hooks 'highlight-changes-enable-hook)))
      ))
    

(defun hilit-chg-turn-off-maybe ()
  (if highlight-changes-mode
      (progn
	(run-hooks 'highlight-changes-disable-hook)
	(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 value)
		   (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