From: Alan Mackenzie <acm@muc.de>
Cc: Richard Stallman <rms@gnu.org>, emacs-devel@gnu.org
Subject: Re: Last steps for pretesting (font-lock-extend-region-function)
Date: Tue, 25 Apr 2006 14:07:29 +0000 (GMT) [thread overview]
Message-ID: <Pine.LNX.3.96.1060425133034.675I-100000@acm.acm> (raw)
In-Reply-To: <87fyk1df9o.fsf-monnier+emacs@gnu.org>
Hi, Stefan!
On Tue, 25 Apr 2006, Stefan Monnier wrote:
>> I find the elisp manual page which describes font-lock-keywords
>> ("Search-based Fontification") all but inpenetrable. It's reduced me to
>> tears on several occasions. I've just spent five minutes looking through
>> it, trying to find the description of the form you suggested to me:
>> (".*\\\\\n.*"
>> (0 (progn (put-text-property (match-beginning 0) (match-end 0)
>> 'font-lock-multiline t)
>> nil)))
>> . I didn't find it.
>This form is the standard form (except you haven't noticed yet that the
>FACENAME part of the font-lock-keywords is not a face symbol but an Elisp
>expression whose value after exavluation should be a face). It's:
> (MATCHER HIGHLIGHT ...)
>where MATCHER is ".*\\\\\n.*" and HIGHLIGHT is of the form MATCH-HIGHLIGHT
>which is of the form (SUBEXP FACENAME [OVERRIDE [LAXMATCH]]) where SUBEXP is
>0 and FACENAME is (progn ...).
OK. So FACENAME comes back as nil (which presumably means "don't apply a
facename property") and the side effect is applying f-l-multiline if the
buffer line matches the regexp.
>> With respect, Stefan, that's rubbish. You need to know where and how
>> to write the above Lisp form (the one starting (".*\\\\n.*" ...)) into
>> f-l-keywords. For me, that's perhaps half an hour to an hour of
>> frustration trying to find the right place in "Search-based
>> Fontification".
>If you don't know how font-lock-keywords work, then learn that first
>before trying to work on the font-lock support for cc-mode. That'll
>save you a lot more time.
I cannot learn it, any more than I could learn logarithm tables when such
were still in use. I need to go through the elisp page every single
time. The same applies to things like c-offsets-alist too, by the way.
>> What about the run-time overhead of having an extra text property over
>> the entire buffer?
>It's not over the entire buffer.
Load a buffer and wait for it to be jit-locked. The entire buffer will
have been scanned and this text property, in effect, set to t or nil on
every single byte.
>And I haven't seen any evidence that it's noticeable (especially
>compared the number of `face' properties or of the `fontified' property
>added to the whole buffer).
I'm sure it's not.
>> The f-l-e-r-f, as you envisage it (being called only from
>> f-l-default-fontify-r) will also be called at virtually every buffer
>> change, since almost every change causes a redisplay.
>AFAIK, the case where a single change takes place between redisplay is the
>case where there is no performance issue: it takes place at the user's
>pace anyway. The important case is when Emacs has more work to do in
>response to a user's action, i.e. there's more work to be done until the
>next redisplay.
Is it really that important to responsiveness whether the delay happens
at the redisplay or immediately after the change? With the after-change
f-l-e-r-f, only the two boundaries of the region get checked, plus any
chunk boundaries when this is bigger than 500 bytes. With the extra
pattern in f-l-keywords, then entire region gets checked.
An after-change f-l-e-r-f needs to be fast enough, and if it's not, that
might be a good reason for using f-l-m instead. However, f-l-m is more
expensive in aggregate - it marks _every_ sequence which must be
atomically fontified, just in case that sequence might straddle a chunk
boundary in the future. Not only that, it erases and recalculates the
property every time it fontifies a region, even when there has been no
buffer change in that region. After-change f-l-e-r-f only checks for
those region boundaries it needs to know immediately.
[ .... ]
>I'm as close as it gets to a font-lock maintainer. So from where I
>stand, you're trying to impose your taste and judgment on me.
I'm as close as it gets to a CC Mode maintainer at the moment. What's
constraining my freedom in that department now? ;-)
[ .... ]
>> My fix is simpler: to recognise that f-l-default-fontify-region
>> performs two disparate tasks: (i) Extending the region to be
>> fontified; (ii) Fontifying this region. By extracting (ii) into a
>> separate function, that function could be called directly from
>> jit-lock-fontify-now, bypassing the redundant second massaging of the
>> region.
>It has to be in font-lock-default-fontify-buffer since there's no
>guarantee this is only called from jit-lock-fontify-now.
No. It has to be _called_ from font-lock-default-fontify-buffer.
>So you're suggesting to add a redundant call to the extend-region hook.
>Maybe it's simpler but it's ugly (because of the redundance, and because
>it adds a dependency between jit-lock and font-lock).
No. I'm suggesting refactoring the font lock code a little so that each
path through it calls the extend-region hook exactly once. Once in the
jit-lock "branch" and once in the plain font lock "branch".
>> (i) It uses the same hook, font-lock-extend-region-function, as
>> f-l-after-change-functions, setting the third parameter, OLD-LEN, to nil;
>> (ii) It uses a distinct hook with a new name, say,
>> font-lock-extend-chunk-function;
>> (iii) It usurps the name f-l-e-r-f from its current use, abolishing the
>> region extension mechanism in the f-l-after-change-f/j-l-after-change.
>(iv) it reuses the name font-lock-extend-region-function and renames the
> a-c-f hook to font-lock-after-change-extend-region-function.
Or that. It's a good job our terminals are wider than 80 columns
nowadays. :-)
>This will happen hopefully today.
Hopefully yes!
>At the same time font-lock-after-change-extend-region-function will be
>moved from font-core to font-lock (where it belongs) and its
>make-variable-buffer-local call will be removed as well (use
>make-local-variable manually if you need it).
Surely not - that variable is essentially buffer local, and it makes no
sense for it not to be so. To remove the make-variable-buffer-local call
could lead to the same problems which have bedevilled paragraph-start and
paragraph-separate.
> Stefan
--
Alan.
next prev parent reply other threads:[~2006-04-25 14:07 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-17 0:56 Last steps for pretesting Richard Stallman
2006-04-17 8:01 ` Ramprasad B
2006-04-17 8:37 ` Eli Zaretskii
2006-04-18 1:42 ` Richard Stallman
2006-04-19 3:54 ` Ramprasad B
2006-04-19 15:40 ` Richard Stallman
2006-04-20 5:23 ` Ramprasad B
2006-04-18 17:31 ` Bill Wohler
2006-04-19 17:02 ` Alan Mackenzie
2006-04-19 21:23 ` Stefan Monnier
2006-04-19 21:30 ` David Kastrup
2006-04-20 21:35 ` Stefan Monnier
2006-04-20 21:37 ` David Kastrup
2006-04-20 21:44 ` Stefan Monnier
2006-04-20 21:46 ` David Kastrup
2006-04-20 22:50 ` Alan Mackenzie
2006-04-19 22:43 ` Last steps for pretesting (font-lock-extend-region-function) Alan Mackenzie
2006-04-20 9:13 ` Alan Mackenzie
2006-04-20 17:46 ` Stefan Monnier
2006-04-20 18:12 ` Alan Mackenzie
2006-04-20 20:58 ` Stefan Monnier
2006-04-20 22:40 ` Alan Mackenzie
2006-04-20 23:34 ` Stefan Monnier
2006-04-21 7:58 ` Alan Mackenzie
2006-04-21 12:18 ` Stefan Monnier
2006-04-21 19:51 ` Alan Mackenzie
2006-04-21 22:28 ` Stefan Monnier
2006-04-24 19:28 ` Alan Mackenzie
2006-04-24 21:06 ` Stefan Monnier
2006-04-25 6:21 ` Ralf Angeli
2006-04-25 10:53 ` Alan Mackenzie
2006-04-25 18:37 ` Ralf Angeli
2006-04-25 22:00 ` Alan Mackenzie
2006-04-26 6:14 ` Ralf Angeli
2006-04-25 19:26 ` Stefan Monnier
2006-04-25 20:10 ` font-lock-multiline for cc-awk Stefan Monnier
2006-04-26 7:37 ` Alan Mackenzie
2006-04-26 13:55 ` Stefan Monnier
2006-04-25 19:23 ` Last steps for pretesting (font-lock-extend-region-function) Stefan Monnier
2006-04-25 20:18 ` Stefan Monnier
2006-04-25 11:33 ` Alan Mackenzie
2006-04-25 11:59 ` David Kastrup
2006-04-25 12:33 ` Stefan Monnier
2006-04-25 14:07 ` Alan Mackenzie [this message]
2006-04-25 16:05 ` Stefan Monnier
2006-04-25 16:09 ` Stefan Monnier
2006-04-25 21:52 ` Alan Mackenzie
2006-04-25 21:49 ` Alan Mackenzie
2006-04-26 4:50 ` Stefan Monnier
2006-04-24 21:20 ` Stefan Monnier
2006-04-25 7:45 ` Alan Mackenzie
2006-04-25 12:12 ` Stefan Monnier
2006-04-25 21:15 ` Alan Mackenzie
2006-04-26 4:33 ` Stefan Monnier
2006-04-26 8:30 ` Alan Mackenzie
2006-04-26 13:36 ` Stefan Monnier
2006-04-24 21:33 ` Stefan Monnier
2006-04-25 7:27 ` Alan Mackenzie
2006-04-25 12:03 ` Stefan Monnier
2006-04-25 13:14 ` Alan Mackenzie
2006-04-26 0:22 ` Miles Bader
2006-04-25 4:39 ` Tomas Zerolo
2006-04-25 19:02 ` Ralf Angeli
2006-04-25 19:30 ` Stefan Monnier
2006-04-25 20:12 ` Ralf Angeli
2006-04-25 20:26 ` Stefan Monnier
2006-04-25 20:58 ` Ralf Angeli
2006-04-25 21:11 ` Stefan Monnier
2006-04-25 22:30 ` Alan Mackenzie
2006-04-26 4:25 ` Stefan Monnier
2006-04-26 7:44 ` Alan Mackenzie
2006-04-25 22:16 ` Alan Mackenzie
2006-04-26 4:36 ` Stefan Monnier
2006-04-21 23:14 ` Drew Adams
2006-04-19 22:53 ` Last steps for pretesting (true file names in load-history?) Alan Mackenzie
2006-04-20 1:14 ` Last steps for pretesting Richard Stallman
2006-04-24 17:52 ` Richard Stallman
2006-04-20 10:54 ` Reiner Steib
2006-04-21 0:10 ` Richard Stallman
2006-04-21 5:46 ` David Kastrup
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