Initial revision

[emacs.git] / lisp / lazy-lock.el

;;; lazy-lock.el --- Lazy demand-driven fontification for fast Font Lock mode.

;; Copyright (C) 1994, 1995, 1996 Free Software Foundation, Inc.

;; Author: Simon Marshall <simon@gnu.ai.mit.edu>
;; Keywords: faces files
;; Version: 2.06

;;; 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:

;; Purpose:
;;
;; To make visiting buffers in `font-lock-mode' faster by making fontification
;; be demand-driven, deferred and stealthy.
;; Fontification only occurs when, and where, necessary.
;;
;; See caveats and feedback below.
;; See also the fast-lock package.  (But don't use them at the same time!)

;; Installation:
;; 
;; Put in your ~/.emacs:
;;
;; (setq font-lock-support-mode 'lazy-lock-mode)
;;
;; Start up a new Emacs and use font-lock as usual (except that you can use the
;; so-called "gaudier" fontification regexps on big files without frustration).
;;
;; In a buffer (which has `font-lock-mode' enabled) which is at least
;; `lazy-lock-minimum-size' characters long, buffer fontification will not
;; occur and only the visible portion of the buffer will be fontified.  Motion
;; around the buffer will fontify those visible portions not previously
;; fontified.  If stealth fontification is enabled, buffer fontification will
;; occur in invisible parts of the buffer after `lazy-lock-stealth-time'
;; seconds of idle time.  If on-the-fly fontification is deferred, on-the-fly
;; fontification will occur after `lazy-lock-defer-time' seconds of idle time.

;; User-visible differences with version 1:
;;
;; - Version 2 can defer on-the-fly fontification.  Therefore you need not, and
;; should not, use defer-lock.el with this version of lazy-lock.el.
;;
;; A number of variables have changed meaning:
;;
;; - A value of nil for the variable `lazy-lock-minimum-size' means never turn
;; on demand-driven fontification.  In version 1 this meant always turn on
;; demand-driven fontification.  If you really want demand-driven fontification
;; regardless of buffer size, set this variable to 0.
;;
;; - The variable `lazy-lock-stealth-lines' cannot have a nil value.  In
;; version 1 this meant use `window-height' as the maximum number of lines to
;; fontify as a stealth chunk.  This makes no sense; stealth fontification is
;; of a buffer, not a window.

;; Implementation differences with version 1:
;;
;; - Version 1 of lazy-lock.el is a bit of a hack.  Version 1 demand-driven
;; fontification, the core feature of lazy-lock.el, is implemented by placing a
;; function on `post-command-hook'.  This function fontifies where necessary,
;; i.e., where a window scroll has occurred.  However, there are a number of
;; problems with using `post-command-hook':
;;
;; (a) As the name suggests, `post-command-hook' is run after every command,
;;     i.e., frequently and regardless of whether scrolling has occurred.
;; (b) Scrolling can occur during a command, when `post-command-hook' is not
;;     run, i.e., it is not necessarily run after scrolling has occurred.
;; (c) When `post-command-hook' is run, there is nothing to suggest where
;;     scrolling might have occurred, i.e., which windows have scrolled.
;;
;; Thus lazy-lock.el's function is called almost as often as possible, usually
;; when it need not be called, yet it is not always called when it is needed.
;; Also, lazy-lock.el's function must check each window to see if a scroll has
;; occurred there.  Worse still, lazy-lock.el's function must fontify a region
;; twice as large as necessary to make sure the window is completely fontified.
;; Basically, `post-command-hook' is completely inappropriate for lazy-lock.el.
;;
;; Ideally, we want to attach lazy-lock.el's function to a hook that is run
;; only when scrolling occurs, e.g., `window-start' has changed, and tells us
;; as much information as we need, i.e., the window and its new buffer region.
;; Richard Stallman implemented a `window-scroll-functions' for Emacs 19.30.
;; Functions on it are run when `window-start' has changed, and are supplied
;; with the window and the window's new `window-start' position.  (It would be
;; better if it also supplied the window's new `window-end' position, but that
;; is calculated as part of the redisplay process, and the functions on
;; `window-scroll-functions' are run before redisplay has finished.)  Thus, the
;; hook deals with the above problems (a), (b) and (c).
;;
;; If only life was that easy.  Version 2 demand-driven fontification is mostly
;; implemented by placing a function on `window-scroll-functions'.  However,
;; not all scrolling occurs when `window-start' has changed.  A change in
;; window size, e.g., via C-x 1, or a significant deletion, e.g., of a number
;; of lines, causes `window-end' to change without changing `window-start'.
;; Arguably, these events are not scrolling events, but fontification must
;; occur for lazy-lock.el to work.  Hooks `window-size-change-functions' and
;; `redisplay-end-trigger-functions' were added for these circumstances.
;;
;; Ben Wing thinks these hooks are "horribly horribly kludgy", and implemented
;; a `pre-idle-hook', a `mother-of-all-post-command-hooks', for XEmacs 19.14.
;; He then hacked up a version 1 lazy-lock.el to use `pre-idle-hook' rather
;; than `post-command-hook'.  Whereas functions on `post-command-hook' are
;; called almost as often as possible, functions on `pre-idle-hook' really are
;; called as often as possible, even when the mouse moves and, on some systems,
;; while XEmacs is idle.  Thus, the hook deals with the above problem (b), but
;; unfortunately it makes (a) worse and does not address (c) at all.
;;
;; I freely admit that `redisplay-end-trigger-functions' and, to a much lesser
;; extent, `window-size-change-functions' are not pretty.  However, I feel that
;; a `window-scroll-functions' feature is cleaner than a `pre-idle-hook', and
;; the result is faster and smaller, less intrusive and more targeted, code.
;; Since `pre-idle-hook' is pretty much like `post-command-hook', there is no
;; point in making this version of lazy-lock.el work with it.  Anyway, that's
;; Lit 30 of my humble opinion.
;;
;; - Version 1 stealth fontification is also implemented by placing a function
;; on `post-command-hook'.  This function waits for a given amount of time,
;; and, if Emacs remains idle, fontifies where necessary.  Again, there are a
;; number of problems with using `post-command-hook':
;;
;; (a) Functions on `post-command-hook' are run sequentially, so this function
;;     can interfere with other functions on the hook, and vice versa.
;; (b) This function waits for a given amount of time, so it can interfere with
;;     various features that are dealt with by Emacs after a command, e.g.,
;;     region highlighting, asynchronous updating and keystroke echoing.
;; (c) Fontification may be required during a command, when `post-command-hook'
;;     is not run.  (Version 2 deferred fontification only.)
;;
;; Again, `post-command-hook' is completely inappropriate for lazy-lock.el.
;; Richard Stallman and Morten Welinder implemented internal Timers and Idle
;; Timers for Emacs 19.31.  Functions can be run independently at given times
;; or after given amounts of idle time.  Thus, the feature deals with the above
;; problems (a), (b) and (c).  Version 2 deferral and stealth are implemented
;; by functions on Idle Timers.  (A function on XEmacs' `pre-idle-hook' is
;; similar to an Emacs Idle Timer function with a fixed zero second timeout.
;; Hey, maybe I could stop using `window-scroll-functions' for demand-driven
;; fontification and use a zero second Emacs Idle Timer instead?  Only joking!)

;; Caveats:
;;
;; Lazy Lock mode does not work efficiently with Outline mode.  This is because
;; when in Outline mode, although text may be hidden (not visible in the
;; window), the text is visible to Emacs Lisp code (not surprisingly) and Lazy
;; Lock fontifies it mercilessly.  Maybe it will be fixed one day.
;;
;; Because buffer text is not necessarily fontified, other packages that expect
;; buffer text to be fontified in Font Lock mode either might not work as
;; expected, or might not display buffer text as expected.  An example of the
;; latter is `occur', which copies lines of buffer text into another buffer.
;;
;; In Emacs 19.30, Lazy Lock mode does not ensure that an existing buffer is
;; fontified if it is made visible via a minibuffer-less command that replaces
;; an existing window's buffer (e.g., via the Buffers menu).  Upgrade!
;;
;; In Emacs 19.30, Lazy Lock mode does not work well with Transient Mark mode
;; or modes based on Comint mode (e.g., Shell mode), and also interferes with
;; the echoing of keystrokes in the minibuffer.  This is because of the way
;; deferral and stealth have to be implemented for Emacs 19.30.  Upgrade!
;;
;; Currently XEmacs does not have the features to support this version of
;; lazy-lock.el.  Maybe it will one day.

;; Feedback:
;;
;; Feedback is welcome.
;; To submit a bug report (or make comments) please use the mechanism provided:
;;
;; M-x lazy-lock-submit-bug-report RET
\f
;; History:
;;
;; 1.15--2.00:
;; - Rewrite for Emacs 19.30 and the features rms added to support lazy-lock.el
;;   so that it could work correctly and efficiently.
;; - Many thanks to those who reported bugs, fixed bugs, made suggestions or
;;   otherwise contributed in the version 1 cycle; Jari Aalto, Kevin Broadey,
;;   Ulrik Dickow, Bill Dubuque, Bob Glickstein, Boris Goldowsky,
;;   Jonas Jarnestrom, David Karr, Michael Kifer, Erik Naggum, Rick Sladkey,
;;   Jim Thompson, Ben Wing, Ilya Zakharevich, and Richard Stallman.
;; 2.00--2.01:
;; - Made `lazy-lock-fontify-after-command' always `sit-for' and so redisplay
;; - Use `buffer-name' not `buffer-live-p' (Bill Dubuque hint)
;; - Made `lazy-lock-install' do `add-to-list' not `setq' of `current-buffer'
;; - Made `lazy-lock-fontify-after-install' loop over buffer list
;; - Made `lazy-lock-arrange-before-change' to arrange `window-end' triggering
;; - Made `lazy-lock-let-buffer-state' wrap both `befter-change-functions'
;; - Made `lazy-lock-fontify-region' do `condition-case' (Hyman Rosen report)
;; 2.01--2.02:
;; - Use `buffer-live-p' as `buffer-name' can barf (Richard Stanton report)
;; - Made `lazy-lock-install' set `font-lock-fontified' (Kevin Davidson report)
;; - Made `lazy-lock-install' add hooks only if needed
;; - Made `lazy-lock-unstall' add `font-lock-after-change-function' if needed
;; 2.02--2.03:
;; - Made `lazy-lock-fontify-region' do `condition-case' for `quit' too
;; - Made `lazy-lock-mode' respect the value of `font-lock-inhibit-thing-lock'
;; - Added `lazy-lock-after-unfontify-buffer'
;; - Removed `lazy-lock-fontify-after-install' hack
;; - Made `lazy-lock-fontify-after-scroll' not `set-buffer' to `window-buffer'
;; - Made `lazy-lock-fontify-after-trigger' not `set-buffer' to `window-buffer'
;; - Made `lazy-lock-fontify-after-idle' be interruptible (Scott Burson hint)
;; 2.03--2.04:
;; - Rewrite for Emacs 19.31 idle timers
;; - Renamed `buffer-windows' to `get-buffer-window-list'
;; - Removed `buffer-live-p'
;; - Made `lazy-lock-defer-after-change' always save `current-buffer'
;; - Made `lazy-lock-fontify-after-defer' just process buffers
;; - Made `lazy-lock-install-hooks' add hooks correctly (Kevin Broadey report)
;; - Made `lazy-lock-install' cope if `lazy-lock-defer-time' is a list
;; 2.04--2.05:
;; - Rewrite for Common Lisp macros
;; - Added `do-while' macro
;; - Renamed `lazy-lock-let-buffer-state' macro to `save-buffer-state'
;; - Returned `lazy-lock-fontify-after-install' hack (Darren Hall hint)
;; - Added `lazy-lock-defer-driven' functionality (Scott Byer hint)
;; - Made `lazy-lock-mode' wrap `font-lock-support-mode'
;; 2.05--2.06:
;; - Made `lazy-lock-fontify-after-defer' swap correctly (Scott Byer report)
\f
(require 'font-lock)

;; Make sure lazy-lock.el is supported.
(if (if (save-match-data (string-match "Lucid\\|XEmacs" (emacs-version)))
        t
      (and (= emacs-major-version 19) (< emacs-minor-version 30)))
    (error "`lazy-lock' was written for Emacs 19.30 or later"))

;; Flush out those lusers who didn't read all of the Commentary.
(if (or (memq 'turn-on-defer-lock font-lock-mode-hook)
        (memq 'defer-lock-mode font-lock-mode-hook))
    (error "`lazy-lock' was written for use without `defer-lock'"))
  
(eval-when-compile
  ;;
  ;; We don't do this at the top-level as idle timers are not necessarily used.
  (require 'timer)
  ;; We don't do this at the top-level as we only use non-autoloaded macros.
  (require 'cl)
  ;;
  ;; Well, shouldn't Lazy Lock mode be as lazy as possible?
  (setq byte-compile-dynamic t byte-compile-dynamic-docstrings t)
  ;; But, we make sure that the code is as zippy as can be.
  (setq byte-optimize t)
  ;;
  ;; We use this to preserve or protect things when modifying text properties.
  (defmacro save-buffer-state (varlist &rest body)
    "Bind variables according to VARLIST and eval BODY restoring buffer state."
    (` (let* ((,@ (append varlist
                   '((modified (buffer-modified-p))
                     (inhibit-read-only t) (buffer-undo-list t)
                     before-change-functions after-change-functions
                     deactivate-mark buffer-file-name buffer-file-truename))))
         (,@ body)
         (when (and (not modified) (buffer-modified-p))
           (set-buffer-modified-p nil)))))
  (put 'save-buffer-state 'lisp-indent-function 1)
  ;;
  ;; We use this for clarity and speed.  Naughty but nice.
  (defmacro do-while (test &rest body)
    "(do-while TEST BODY...): eval BODY... and repeat if TEST yields non-nil.
The order of execution is thus BODY, TEST, BODY, TEST and so on
until TEST returns nil."
    (` (while (progn (,@ body) (, test)))))
  (put 'do-while 'lisp-indent-function (get 'while 'lisp-indent-function)))
\f
;; User Variables:

(defvar lazy-lock-minimum-size (* 25 1024)
  "*Minimum size of a buffer for demand-driven fontification.
On-demand fontification occurs if the buffer size is greater than this value.
If nil, means demand-driven fontification is never performed.
If a list, each element should be a cons pair of the form (MAJOR-MODE . SIZE),
where MAJOR-MODE is a symbol or t (meaning the default).  For example:
 ((c-mode . 25600) (c++-mode . 25600) (rmail-mode . 1048576))
means that the minimum size is 25K for buffers in C or C++ modes, one megabyte
for buffers in Rmail mode, and size is irrelevant otherwise.

The value of this variable is used when Lazy Lock mode is turned on.")

(defvar lazy-lock-defer-driven nil
  "*If non-nil, means fontification should be defer-driven.
If nil, means demand-driven fontification is performed.  This means when
scrolling into unfontified areas of the buffer, those areas are immediately
fontified.  Thus scrolling never presents unfontified areas.  However, since
fontification occurs during scrolling, scrolling may be slow.
If t, means defer-driven fontification is performed.  This means fontification
of those areas is deferred.  Thus scrolling may present momentarily unfontified
areas.  However, since fontification does not occur during scrolling, scrolling
will be faster than demand-driven fontification.
If any other value, e.g., `eventually', means demand-driven fontification is
performed until the buffer is fontified, then buffer fontification becomes
defer-driven.  Thus scrolling never presents unfontified areas until the buffer
is first fontified, after which subsequent scrolling may present future buffer
insertions momentarily unfontified.  However, since fontification does not
occur during scrolling after the buffer is first fontified, scrolling will
become faster.

The value of this variable is used when Lazy Lock mode is turned on.")

(defvar lazy-lock-defer-time
  (if (featurep 'lisp-float-type) (/ (float 1) (float 4)) 1)
  "*Time in seconds to delay before beginning deferred fontification.
Deferred fontification occurs if there is no input within this time.
If nil, means fontification is never deferred.  However, fontification occurs
on-the-fly or during scrolling, which may be slow.
If a list, it should be of the form (MAJOR-MODES . TIME), where MAJOR-MODES is
a list of `major-mode' symbols for which deferred fontification should occur.
The sense of the list is negated if it begins with `not'.  For example:
 ((c-mode c++-mode) . 0.25)
means that the deferral time is 0.25s for buffers in C or C++ modes, and
deferral does not occur otherwise.

The value of this variable is used when Lazy Lock mode is turned on.")

(defvar lazy-lock-stealth-time 30
  "*Time in seconds to delay before beginning stealth fontification.
Stealth fontification occurs if there is no input within this time.
If nil, means stealth fontification is never performed.

The value of this variable is used when Lazy Lock mode is turned on.")

(defvar lazy-lock-stealth-lines (if font-lock-maximum-decoration 100 250)
  "*Maximum size of a chunk of stealth fontification.
Each iteration of stealth fontification can fontify this number of lines.
To speed up input response during stealth fontification, at the cost of stealth
taking longer to fontify, you could reduce the value of this variable.")

(defvar lazy-lock-stealth-nice
  (if (featurep 'lisp-float-type) (/ (float 1) (float 8)) 1)
  "*Time in seconds to pause between chunks of stealth fontification.
Each iteration of stealth fontification is separated by this amount of time.
To reduce machine load during stealth fontification, at the cost of stealth
taking longer to fontify, you could increase the value of this variable.")

(defvar lazy-lock-stealth-verbose (not (null font-lock-verbose))
  "*If non-nil, means stealth fontification should show status messages.")

(defvar lazy-lock-mode nil)
(defvar lazy-lock-buffers nil)                  ; for deferral
(defvar lazy-lock-timers (cons nil nil))        ; for deferral and stealth
\f
;; User Functions:

;;;###autoload
(defun lazy-lock-mode (&optional arg)
  "Toggle Lazy Lock mode.
With arg, turn Lazy Lock mode on if and only if arg is positive.  Enable it
automatically in your `~/.emacs' by:

 (setq font-lock-support-mode 'lazy-lock-mode)

When Lazy Lock mode is enabled, fontification can be lazy in a number of ways:

 - Demand-driven buffer fontification if `lazy-lock-minimum-size' is non-nil.
   This means initial fontification does not occur if the buffer is greater
   than `lazy-lock-minimum-size' characters in length.  Instead, fontification
   occurs when necessary, such as when scrolling through the buffer would
   otherwise reveal unfontified areas.  This is useful if buffer fontification
   is too slow for large buffers.

 - Defer-driven buffer fontification if `lazy-lock-defer-driven' is non-nil.
   This means all fontification is deferred, such as fontification that occurs
   when scrolling through the buffer would otherwise reveal unfontified areas.
   Instead, these areas are seen momentarily unfontified.  This is useful if
   demand-driven fontification is too slow to keep up with scrolling.

 - Deferred on-the-fly fontification if `lazy-lock-defer-time' is non-nil.
   This means on-the-fly fontification does not occur as you type.  Instead,
   fontification is deferred until after `lazy-lock-defer-time' seconds of
   Emacs idle time, while Emacs remains idle.  This is useful if on-the-fly
   fontification is too slow to keep up with your typing.

 - Stealthy buffer fontification if `lazy-lock-stealth-time' is non-nil.
   This means remaining unfontified areas of buffers are fontified if Emacs has
   been idle for `lazy-lock-stealth-time' seconds, while Emacs remains idle.
   This is useful if any buffer has demand- or defer-driven fontification.

See also variables `lazy-lock-stealth-lines', `lazy-lock-stealth-nice' and
`lazy-lock-stealth-verbose' for stealth fontification.

Use \\[lazy-lock-submit-bug-report] to send bug reports or feedback."
  (interactive "P")
  (set (make-local-variable 'lazy-lock-mode)
       (and (not (memq 'lazy-lock-mode font-lock-inhibit-thing-lock))
            (if arg (> (prefix-numeric-value arg) 0) (not lazy-lock-mode))))
  (cond ((and lazy-lock-mode (not font-lock-mode))
         ;; Turned on `lazy-lock-mode' rather than `font-lock-mode'.
         (let ((font-lock-support-mode 'lazy-lock-mode))
           (font-lock-mode t)))
        (lazy-lock-mode
         ;; Turn ourselves on.
         (lazy-lock-install))
        (t
         ;; Turn ourselves off.
         (lazy-lock-unstall))))

(defun lazy-lock-submit-bug-report ()
  "Submit via mail a bug report on lazy-lock.el."
  (interactive)
  (let ((reporter-prompt-for-summary-p t))
    (reporter-submit-bug-report "simon@gnu.ai.mit.edu" "lazy-lock 2.06"
     '(lazy-lock-minimum-size lazy-lock-defer-driven lazy-lock-defer-time
       lazy-lock-stealth-time lazy-lock-stealth-nice lazy-lock-stealth-lines
       lazy-lock-stealth-verbose)
     nil nil
     (concat "Hi Si.,

I want to report a bug.  I've read the `Bugs' section of `Info' on Emacs, so I
know how to make a clear and unambiguous report.  To reproduce the bug:

Start a fresh Emacs via `" invocation-name " -no-init-file -no-site-file'.
In the `*scratch*' buffer, evaluate:"))))

;;;###autoload
(defun turn-on-lazy-lock ()
  "Unconditionally turn on Lazy Lock mode."
  (lazy-lock-mode t))

(defun lazy-lock-install ()
  (let ((min-size (font-lock-value-in-major-mode lazy-lock-minimum-size)))
    ;;
    ;; Tell Font Lock whether Lazy Lock will do fontification.
    (make-local-variable 'font-lock-fontified)
    (setq font-lock-fontified (and min-size (>= (buffer-size) min-size)))
    ;;
    ;; Add the text properties and fontify.
    (if (not font-lock-fontified)
        (lazy-lock-after-fontify-buffer)
      ;; Make sure we fontify in any existing windows showing the buffer.
      (let ((windows (get-buffer-window-list (current-buffer) 'nomini t)))
        (lazy-lock-after-unfontify-buffer)
        (while windows
          (lazy-lock-fontify-conservatively (car windows))
          (setq windows (cdr windows)))))
    ;;
    ;; Add the fontification hooks.
    (lazy-lock-install-hooks
     (or (numberp lazy-lock-defer-time)
         (if (eq (car (car lazy-lock-defer-time)) 'not)
             (not (memq major-mode (cdr (car lazy-lock-defer-time))))
           (memq major-mode (car lazy-lock-defer-time))))
     font-lock-fontified
     (eq lazy-lock-defer-driven t))
    ;;
    ;; Add the fontification timers.
    (lazy-lock-install-timers
     (or (cdr-safe lazy-lock-defer-time) lazy-lock-defer-time)
     lazy-lock-stealth-time)))

(defun lazy-lock-install-hooks (deferring fontifying defer-driven)
  ;;
  ;; Add hook if lazy-lock.el is deferring or is fontifying on scrolling.
  (when (or deferring fontifying)
    (make-local-hook 'window-scroll-functions)
    (add-hook 'window-scroll-functions (if (and deferring defer-driven)
                                           'lazy-lock-defer-after-scroll
                                         'lazy-lock-fontify-after-scroll)
              nil t))
  ;;
  ;; Add hook if lazy-lock.el is not deferring and is fontifying.
  (when (and (not deferring) fontifying)
    (make-local-hook 'before-change-functions)
    (add-hook 'before-change-functions 'lazy-lock-arrange-before-change nil t))
  ;;
  ;; Add hook if lazy-lock.el is deferring.
  (when deferring
    (remove-hook 'after-change-functions 'font-lock-after-change-function t)
    (add-hook 'after-change-functions 'lazy-lock-defer-after-change nil t))
  ;;
  ;; Add package-specific hooks.
  (make-local-hook 'outline-view-change-hook)
  (add-hook 'outline-view-change-hook 'lazy-lock-fontify-after-outline nil t))

(defun lazy-lock-install-timers (dtime stime)
  ;; Schedule or re-schedule the deferral and stealth timers.
  ;; The layout of `lazy-lock-timers' is:
  ;;  ((DEFER-TIME . DEFER-TIMER) (STEALTH-TIME . STEALTH-TIMER)
  ;; If an idle timeout has changed, cancel the existing idle timer (if there
  ;; is one) and schedule a new one (if the new idle timeout is non-nil).
  (unless (eq dtime (car (car lazy-lock-timers)))
    (let ((defer (car lazy-lock-timers)))
      (when (cdr defer)
        (cancel-timer (cdr defer)))
      (setcar lazy-lock-timers (cons dtime (and dtime
              (run-with-idle-timer dtime t 'lazy-lock-fontify-after-defer))))))
  (unless (eq stime (car (cdr lazy-lock-timers)))
    (let ((stealth (cdr lazy-lock-timers)))
      (when (cdr stealth)
        (cancel-timer (cdr stealth)))
      (setcdr lazy-lock-timers (cons stime (and stime
              (run-with-idle-timer stime t 'lazy-lock-fontify-after-idle)))))))

(defun lazy-lock-unstall ()
  ;;
  ;; Remove the text properties.
  (lazy-lock-after-unfontify-buffer)
  ;;
  ;; Remove the fontification hooks.
  (remove-hook 'window-scroll-functions 'lazy-lock-fontify-after-scroll t)
  (remove-hook 'window-scroll-functions 'lazy-lock-defer-after-scroll t)
  (remove-hook 'before-change-functions 'lazy-lock-arrange-before-change t)
  (remove-hook 'after-change-functions 'lazy-lock-defer-after-change t)
  (remove-hook 'outline-view-change-hook 'lazy-lock-fontify-after-outline t)
  ;;
  ;; If Font Lock mode is still enabled, reinstall its hook.
  (when font-lock-mode
    (add-hook 'after-change-functions 'font-lock-after-change-function nil t)))
\f
;; Hook functions.

(defun lazy-lock-fontify-after-scroll (window window-start)
  ;; Called from `window-scroll-functions'.
  ;; Fontify WINDOW from WINDOW-START.  We cannot use `window-end' so we work
  ;; out what it would be via `vertical-motion'.
  (save-excursion
    (goto-char window-start)
    (vertical-motion (window-height window) window)
    (lazy-lock-fontify-region window-start (point)))
  ;; A prior deletion that did not cause scrolling, followed by a scroll, would
  ;; result in an unnecessary trigger after this if we did not cancel it now.
  (set-window-redisplay-end-trigger window nil))

(defun lazy-lock-fontify-after-trigger (window trigger-point)
  ;; Called from `redisplay-end-trigger-functions'.
  ;; Fontify WINDOW from TRIGGER-POINT.  We cannot use `window-end' so we work
  ;; out what it would be via `vertical-motion'.
  ;; We could probably just use `lazy-lock-fontify-after-scroll' without loss:
  ;;  (lazy-lock-fontify-after-scroll window (window-start window))
  (save-excursion
    (goto-char (window-start window))
    (vertical-motion (window-height window) window)
    (lazy-lock-fontify-region trigger-point (point))))

(defun lazy-lock-fontify-after-resize (frame)
  ;; Called from `window-size-change-functions'.
  ;; Fontify windows in FRAME.  We cannot use `window-start' or `window-end' so
  ;; we fontify conservatively.
  (save-excursion
    (save-selected-window
      (select-frame frame)
      (walk-windows (function (lambda (window)
                       (set-buffer (window-buffer window))
                       (when lazy-lock-mode
                         (lazy-lock-fontify-conservatively window))
                       (set-window-redisplay-end-trigger window nil)))
                    'nomini frame))))

(defun lazy-lock-arrange-before-change (beg end)
  ;; Called from `before-change-functions'.
  ;; Arrange that if text becomes visible it will be fontified (if a deletion
  ;; is pending, text might become visible at the bottom).
  (unless (eq beg end)
    (let ((windows (get-buffer-window-list (current-buffer) 'nomini t)) window)
      (while windows
        (setq window (car windows))
        (unless (markerp (window-redisplay-end-trigger window))
          (set-window-redisplay-end-trigger window (make-marker)))
        (set-marker (window-redisplay-end-trigger window) (window-end window))
        (setq windows (cdr windows))))))

(defun lazy-lock-defer-after-scroll (window window-start)
  ;; Called from `window-scroll-functions'.
  ;; Defer fontification following the scroll.  Save the current buffer so that
  ;; we subsequently fontify in all windows showing the buffer.
  (unless (memq (current-buffer) lazy-lock-buffers)
    (push (current-buffer) lazy-lock-buffers)))

(defun lazy-lock-defer-after-change (beg end old-len)
  ;; Called from `after-change-functions'.
  ;; Defer fontification of the current line.  Save the current buffer so that
  ;; we subsequently fontify in all windows showing the buffer.
  (save-buffer-state nil
    (unless (memq (current-buffer) lazy-lock-buffers)
      (push (current-buffer) lazy-lock-buffers))
    (remove-text-properties
     (max (1- beg) (point-min)) (min (1+ end) (point-max)) '(lazy-lock nil))))

(defun lazy-lock-fontify-after-defer ()
  ;; Called from `timer-idle-list'.
  ;; Fontify all windows where deferral has occurred for its buffer.
  (while (and lazy-lock-buffers (not (input-pending-p)))
    (let ((windows (get-buffer-window-list (car lazy-lock-buffers) 'nomini t)))
      (while windows
        (lazy-lock-fontify-window (car windows))
        (setq windows (cdr windows)))
      (setq lazy-lock-buffers (cdr lazy-lock-buffers))))
  ;; Add hook if fontification should now be defer-driven in this buffer.
  (when (and lazy-lock-mode lazy-lock-defer-driven
             (memq 'lazy-lock-fontify-after-scroll window-scroll-functions)
             (not (or (input-pending-p) (lazy-lock-unfontified-p))))
    (remove-hook 'window-scroll-functions 'lazy-lock-fontify-after-scroll t)
    (add-hook 'window-scroll-functions 'lazy-lock-defer-after-scroll nil t)))

(defun lazy-lock-fontify-after-idle ()
  ;; Called from `timer-idle-list'.
  ;; Fontify all buffers that need it, stealthily while idle.
  (unless (or executing-kbd-macro (window-minibuffer-p (selected-window)))
    ;; Loop over all buffers, fontify stealthily for each if necessary.
    (let ((buffers (buffer-list)) (continue t) message message-log-max)
      (save-excursion
        (do-while (and buffers continue)
          (set-buffer (car buffers))
          (if (not (and lazy-lock-mode (lazy-lock-unfontified-p)))
              (setq continue (not (input-pending-p)))
            ;; Fontify regions in this buffer while there is no input.
            (do-while (and (lazy-lock-unfontified-p)
                           (setq continue (sit-for lazy-lock-stealth-nice)))
              (when lazy-lock-stealth-verbose
                (if message
                    (message "Fontifying stealthily... %2d%% of %s"
                             (lazy-lock-percent-fontified) (buffer-name))
                  (message "Fontifying stealthily...")
                  (setq message t)))
              (lazy-lock-fontify-chunk)))
          (setq buffers (cdr buffers))))
      (when message
        (message "Fontifying stealthily...%s" (if continue "done" "quit"))))))

(defun lazy-lock-fontify-after-outline ()
  ;; Called from `outline-view-change-hook'.
  ;; Fontify windows showing the current buffer, as its visibility has changed.
  ;; This is a conspiracy hack between lazy-lock.el and noutline.el.
  (let ((windows (get-buffer-window-list (current-buffer) 'nomini t)))
    (while windows
      (lazy-lock-fontify-conservatively (car windows))
      (setq windows (cdr windows)))))

(defun lazy-lock-after-fontify-buffer ()
  ;; Called from `font-lock-after-fontify-buffer'.
  ;; Mark the current buffer as fontified.
  ;; This is a conspiracy hack between lazy-lock.el and font-lock.el.
  (save-buffer-state nil
    (add-text-properties (point-min) (point-max) '(lazy-lock t))))

(defun lazy-lock-after-unfontify-buffer ()
  ;; Called from `font-lock-after-unfontify-buffer'.
  ;; Mark the current buffer as unfontified.
  ;; This is a conspiracy hack between lazy-lock.el and font-lock.el.
  (save-buffer-state nil
    (remove-text-properties (point-min) (point-max) '(lazy-lock nil))))
\f
;; Fontification functions.

;; If packages want to ensure that some region of the buffer is fontified, they
;; should use this function.  For an example, see ps-print.el.
(defun lazy-lock-fontify-region (beg end)
  ;; Fontify between BEG and END, where necessary, in the current buffer.
  (when (setq beg (text-property-any beg end 'lazy-lock nil))
    (save-excursion
      (save-match-data
        (save-buffer-state
            ;; Ensure syntactic fontification is always correct.
            (font-lock-beginning-of-syntax-function next)
          ;; Find successive unfontified regions between BEG and END.
          (condition-case data
              (do-while beg
                (setq next (or (text-property-any beg end 'lazy-lock t) end))
                ;; Make sure the region end points are at beginning of line.
                (goto-char beg)
                (unless (bolp)
                  (beginning-of-line)
                  (setq beg (point)))
                (goto-char next)
                (unless (bolp)
                  (forward-line)
                  (setq next (point)))
                ;; Fontify the region, then flag it as fontified.
                (font-lock-fontify-region beg next)
                (add-text-properties beg next '(lazy-lock t))
                (setq beg (text-property-any next end 'lazy-lock nil)))
            ((error quit) (message "Fontifying region...%s" data))))))))

(defun lazy-lock-fontify-chunk ()
  ;; Fontify the nearest chunk, for stealth, in the current buffer.
  (save-excursion
    (save-restriction
      (widen)
      ;; Move to end of line in case the character at point is not fontified.
      (end-of-line)
      ;; Find where the previous, and next, unfontified regions end, and begin.
      (let ((prev (previous-single-property-change (point) 'lazy-lock))
            (next (text-property-any (point) (point-max) 'lazy-lock nil)))
        ;; Fontify from the nearest unfontified position.
        (if (or (null prev) (and next (< (- next (point)) (- (point) prev))))
            ;; The next, or neither, region is the nearest not fontified.
            (lazy-lock-fontify-region
             (progn (goto-char (or next (point-min)))
                    (beginning-of-line)
                    (point))
             (progn (goto-char (or next (point-min)))
                    (forward-line lazy-lock-stealth-lines)
                    (point)))
          ;; The previous region is the nearest not fontified.
          (lazy-lock-fontify-region
           (progn (goto-char prev)
                  (forward-line (- lazy-lock-stealth-lines))
                  (point))
           (progn (goto-char prev)
                  (forward-line)
                  (point))))))))

(defun lazy-lock-fontify-window (window)
  ;; Fontify in WINDOW between `window-start' and `window-end'.
  ;; We can only do this when we can use `window-start' and `window-end'.
  (save-excursion
    (set-buffer (window-buffer window))
    (lazy-lock-fontify-region (window-start window) (window-end window))))

(defun lazy-lock-fontify-conservatively (window)
  ;; Fontify in WINDOW conservatively around point.
  ;; Where we cannot use `window-start' and `window-end' we do `window-height'
  ;; lines around point.  That way we guarantee to have done enough.
  (save-excursion
    (set-buffer (window-buffer window))
    (lazy-lock-fontify-region
     (save-excursion
       (vertical-motion (- (window-height window)) window) (point))
     (save-excursion
       (vertical-motion (window-height window) window) (point)))))

(defun lazy-lock-unfontified-p ()
  ;; Return non-nil if there is anywhere still to be fontified.
  (save-restriction
    (widen)
    (text-property-any (point-min) (point-max) 'lazy-lock nil)))

(defun lazy-lock-percent-fontified ()
  ;; Return the percentage (of characters) of the buffer that are fontified.
  (save-restriction
    (widen)
    (let ((beg (point-min)) (end (point-max)) (size 0) next)
      ;; Find where the next fontified region begins.
      (while (setq beg (text-property-any beg end 'lazy-lock t))
        (setq next (or (text-property-any beg end 'lazy-lock nil) end)
              size (+ size (- next beg))
              beg next))
      (/ (* size 100) (buffer-size)))))
\f
;; Version dependent workarounds and fixes.

(when (if (save-match-data (string-match "Lucid\\|XEmacs" (emacs-version)))
          nil
        (and (= emacs-major-version 19) (= emacs-minor-version 30)))
  ;;
  ;; We use `post-command-idle-hook' for deferral and stealth.  Oh Lordy.
  (defun lazy-lock-install-timers (foo bar)
    (add-hook 'post-command-idle-hook 'lazy-lock-fontify-post-command t)
    (add-hook 'post-command-idle-hook 'lazy-lock-fontify-post-idle t)
    (add-to-list 'lazy-lock-install (current-buffer))
    (add-hook 'post-command-hook 'lazy-lock-fontify-after-install))
  (defun lazy-lock-fontify-post-command ()
    (and lazy-lock-buffers (not executing-kbd-macro)
         (progn
           (and deactivate-mark (deactivate-mark))
           (sit-for
            (or (cdr-safe lazy-lock-defer-time) lazy-lock-defer-time 0)))
         (lazy-lock-fontify-after-defer)))
  (defun lazy-lock-fontify-post-idle ()
    (and lazy-lock-stealth-time (not executing-kbd-macro)
         (not (window-minibuffer-p (selected-window)))
         (progn
           (and deactivate-mark (deactivate-mark))
           (sit-for lazy-lock-stealth-time))
         (lazy-lock-fontify-after-idle)))
  ;;
  ;; Simulate running of `window-scroll-functions' in `set-window-buffer'.
  (defvar lazy-lock-install nil)
  (defun lazy-lock-fontify-after-install ()
    (remove-hook 'post-command-hook 'lazy-lock-fontify-after-install)
    (while lazy-lock-install
      (mapcar 'lazy-lock-fontify-conservatively
              (get-buffer-window-list (pop lazy-lock-install) 'nomini t)))))
\f
;; Possibly absent.

(unless (boundp 'font-lock-inhibit-thing-lock)
  ;; Font Lock mode uses this to direct Lazy and Fast Lock modes to stay off.
  (defvar font-lock-inhibit-thing-lock nil
    "List of Font Lock mode related modes that should not be turned on."))

(unless (fboundp 'font-lock-value-in-major-mode)
  (defun font-lock-value-in-major-mode (alist)
    ;; Return value in ALIST for `major-mode'.
    (if (consp alist)
        (cdr (or (assq major-mode alist) (assq t alist)))
      alist)))

(unless (fboundp 'get-buffer-window-list)
  ;; We use this to get all windows showing a buffer we have to fontify.
  (defun get-buffer-window-list (buffer &optional minibuf frame)
    "Return windows currently displaying BUFFER, or nil if none."
    (let ((buffer (if (bufferp buffer) buffer (get-buffer buffer))) windows)
      (walk-windows (function (lambda (window)
                                (when (eq (window-buffer window) buffer)
                                  (push window windows))))
                    minibuf frame)
      windows)))
\f
;; Install ourselves:

(add-hook 'window-size-change-functions 'lazy-lock-fontify-after-resize)
(add-hook 'redisplay-end-trigger-functions 'lazy-lock-fontify-after-trigger)

(unless (assq 'lazy-lock-mode minor-mode-alist)
  (setq minor-mode-alist (append minor-mode-alist '((lazy-lock-mode nil)))))

;; Provide ourselves:

(provide 'lazy-lock)

;;; lazy-lock.el ends here