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Re: font-lock-extend-region (was: address@hidden: C++-mode: Syntax highl
From: |
Alan Mackenzie |
Subject: |
Re: font-lock-extend-region (was: address@hidden: C++-mode: Syntax highlighting: wrong color for function identifier depending on the kind of whitespace that follows]) |
Date: |
Mon, 20 Mar 2006 13:01:00 +0000 (GMT) |
Hi, Stefan!
Before I get going, I'd like to say I've spent some time getting to grips
with jit-lock, and I think I now understand some of the things you were
telling me. I also apologize for getting a bit grumpy about it last
week.
Here is a diagram of the sequence of functions that a piece of text is
processed by:
#########################################################################
"*" means that the routine adjusts the region to whole lines.
DEMAND (called by display code) <----------------------------|
[fontification-functions] (hook) |
jit-lock-function ->-| |
|-------------<------------+ <is defer-fontif. enabled?> |
| | |
| v ^
| |-----------<------------| |
| | |
| |->* jit-lock-fontify-now <----------------------------| |
| [jit-lock-functions] (hook) | |
v font-lock-fontify-region <------------------------+---+----|
| [font-lock-fontify-region-function] (hook) | | |
| * font-lock-default-fontify-region | | |
| | | |
|DEFERRED (invoked by jit-lock-defer-timer) | | |
|--> jit-lock-deferred-fontify ------------------>-----+---| |
This sets 'fontified to nil, and calls sit-for, | | |
causing immediate display (by DEMAND). | | |
| | |
STEALTH (invoked by jit-lock-stealth-timer) | | |
jit-lock-stealth-fontify | ^ |
jit-lock-fontify-now ----------------->-------------| | |
| |
CONTEXT (invoked by jit-lock-context-timer) | |
jit-lock-context-fontify (from timer) -------->---------+ |
This sets 'fontified to nil on the (extended) | |
region. | |
| |
JIT AFTER CHANGE (called from the after-change hook) | ^
* jit-lock-after-change --------------->------------------| |
This sets 'fontified to nil, and relies on DEMAND |
to refontify the changed bit during display. |
|
ORDINARY AFTER CHANGE (without jit, called from after-change) |
* font-lock-after-change-function |
font-lock-fontify-region ---------------->-------------------|
|
COMMANDS |
font-lock-fontify-block |
font-lock-fontify-region ---------------->-------------------|
|
font-lock-fontify-buffer |
[font-lock-fontify-buffer-function] (hook) |
font-lock-default-fontify-buffer |
font-lock-fontify-region ---------------->-------------------|
#########################################################################
On Mon, 20 Mar 2006, Stefan Monnier wrote:
>OK, having thought some more about it, I'm really convinced doing it
>[extending the fontification region with
>font-lock-extend-region-function] in after-change-function is the wrong
>way: your jit-lock code won't always do the right thing, because even
>though you mark the whole extended region for refontification, jit-lock
>may refontify it in chunks (and maybe not even in the intended order).
OK, I see what you're saying, now, I think - if you insert a large chunk
of text with C-y, font-lock-extend-region will calculate a starting
position off the top of the screen. The display engine will then,
however, call jit-lock-function with the screen beginning as the place to
start, and this won't work properly. I agree with you now.
>So I will move the font-lock-extend-region code to
>font-lock-default-fontify-region where it belongs (which is why that's
>also the place where font-lock-extra-lines was handled and where
>font-lock-multiline is handled).
I think there are two distinct issues here that we're confusing, and this
is why we've found it so hard to agree:
(i) calculating the region which needs refontifying.
(ii) finding a safe place to start fontifying a single chunk.
font-lock-extend-region-function is intended to do (i). The
functionality you're suggesting for f-l-default-fontify-region is for
doing (ii).
>Now IIUC that means it'll break some/all of your uses of that variable.
>Clearly you won't be pleased, but think about it this way: it'll save
>you bug reports from users seeing odd behavior in conjunction with
>jit-lock.
OK, I understand this now.
>Anyway, as I said, for your use case what you should be using is an
>after-change-functions hook that puts a font-lock-multiline property.
>But as you noted, this will only work if your hook happens to be placed
>in after-change-functions before font-lock's own (or jit-lock's, though
>that one is much less serious).
I think the essence of the font-lock-multiline property is that it marks
a chunk of text to be fontified atomically. Please confirm this
impression or correct it for me.
Here's why I think the font-lock-muliline way is wrong. Taking my AWK
example again:
1. "string \
2. over \
3. several \ <=========
4. #lines."
Suppose the user replaces the backslash on L3 with 20k of code from the
kill ring with M-y. The region to fontify now extends from L1 to EOL4
(actually, it's now L1073). The display engine is going to request
fontification from L1034. If I mark this entire region with
font-lock-multiline, these 1073 lines will be (unnecessarily) fontified
atomically, defeating the aims of jit-lock in this case. What I think we
need is a function called from f-l-default-f-region which will get a safe
starting position at or before L1034.
>Also as I mentioned elsewhere, another solution is to change your
>requirement such that some of the responsibility of the refontification
>is passed on to contextual refontification: I would tend to prefer this
>solution myself (it moves work away from the time-critical path). But
>admittedly, setting jit-lock-context-time to 0 is believed to be a bit
>too costly right now (not enough optimizations), so if you really want
>the refontification to be immediate (rather than delayed by 0.5 idle
>seconds), it's not a good solution.
I do, and it's not. :-)
>So what I offer you is to introduce a new
>`font-lock-before-after-change-functions' which is just like
>after-change-functions except it's run by font-lock's (or jit-lock's)
>after-change-function and before it does anything else. You can then
>use this hook to place a function that computes the extended region and
>places a font-lock-multiline property on it.
For the reasons I've given above, I don't think this is the right thing
to do. What I think we should do is to put a hook into
f-l-default-f-region to calculate a safe starting position (and probably
also a safe stopping position).
>Do we have a deal?
Not quite. But I'm sure we'll soon be there. :-)
Incidentally, referring to my diagram above, the region gets extended to
whole lines more than once. For demand fontification, it is done first
in jit-lock-fontify-now then in font-lock-default-fontify-region. For
after-change fontification, it is done yet a third time in
jit-lock-after-change.
How about doing this only in f-l-default-f-r? This would make it easier
for a mode maintainer to switch off this action, since he would then just
have to put a modified function into the hook
font-lock-fontify-region-function.
> Stefan
--
Alan.
- Re: address@hidden: C++-mode: Syntax highlighting: wrong color for function identifier depending on the kind of whitespace that follows], Alan Mackenzie, 2006/03/14
- Re: address@hidden: C++-mode: Syntax highlighting: wrong color for function identifier depending on the kind of whitespace that follows], Stefan Monnier, 2006/03/14
- Re: address@hidden: C++-mode: Syntax highlighting: wrong color for function identifier depending on the kind of whitespace that follows], Richard Stallman, 2006/03/15
- font-lock-extend-region (was: address@hidden: C++-mode: Syntax highlighting: wrong color for function identifier depending on the kind of whitespace that follows]), Stefan Monnier, 2006/03/20
- Re: font-lock-extend-region (was: address@hidden: C++-mode: Syntax highlighting: wrong color for function identifier depending on the kind of whitespace that follows]),
Alan Mackenzie <=
- Re: font-lock-extend-region, Stefan Monnier, 2006/03/20
- Re: font-lock-extend-region, Alan Mackenzie, 2006/03/27
- Re: font-lock-extend-region, Stefan Monnier, 2006/03/27
- Re: font-lock-extend-region, Alan Mackenzie, 2006/03/23
- Re: font-lock-extend-region, Stefan Monnier, 2006/03/23