From: martin rudalics <rudalics@gmx.at>
To: Alan Mackenzie <acm@muc.de>
Cc: 16526-done@debbugs.gnu.org
Subject: bug#16526: 24.3.50; scroll-conservatively & c-mode regression
Date: Mon, 30 Jun 2014 09:55:02 +0200 [thread overview]
Message-ID: <53B117D6.1050306__7893.28965261138$1404114999$gmane$org@gmx.at> (raw)
In-Reply-To: <20140629174953.GE2948@acm.acm>
>> How can any of these affect the cached start position of a defun before
>> the position where the buffer contents were changed?
>
> In this context, the "start of defun" means an outermost paren of some
> sort, nothing more, nothing less. Any of the changes above could disturb
> this: For example, adding an open-paren syntax-table property to a
> character which thereby becomes the BOD. Or temporarily switching to the
> Pascal syntax table, where "{" and "}" are comment brackets. I'm not
> saying that something like this will happen on a regular basis, but it's
> definitely possible.
Then you can forget caching.
>> > Also, the syntax-ppss cache's functioning is dependent upon
>> > before-change-functions, which can be bound to nil by any program at any
>> > time.
>
>> There's an appropriate advice what to do in such case.
>
> Primitive functions are deaf to advice. You're surely not suggesting
> that a primitive like scan-lists should become vulnerable to high-level
> programmers failing to follow advice? If this were to be done,
> scan-lists would only work most of the time, not all of the time. This
> would be catastrophic for Emacs.
I meant that if someone is going to disable `before-change-functions'
that someone has to take care of flushing the cache.
> An example of what? What I meant was, each time you used syntax-ppss
> from scan-lists, you'd somehow need to be sure that a syntax-table entry
> hadn't been changed, etc. I can't really see how this would be possible.
> You'd somehow need to handle constructs like
>
> (with-syntax-table c++-template-syntax-table
> ....
> (scan-lists (point) -1 1)
> ....)
>
> .
And how would a defun start cache handle such constructs?
> No. scan-lists works according to its spec even if you start it inside a
> comment/string. It's effect is well defined. For example if you writen
> parens inside a comment, C-M-n and friends do the right thing there.
Here C-M-n is bound to `forward-list' which according to its doc-string
"assumes point is not in a string or comment". `scan-lists' has
precisely the same problems as `syntax-ppss' wrt syntax changes.
>> So `syntax-ppss' is at least as primitive as `scan-lists' (especially
>> when the latter is used with negative COUNT).
>
> Sorry, but that's utter rubbish. syntax-ppss is a high-level convenience
> function, which if used carefully by the lisp programmer gives correct
> results.
We're not talking about `scan-lists' alone. We're talking about
`scan-lists' (or more precisely find_defun_start) with a cache of
previously calculated positions.
> By contrast, scan-lists does precisely what it says, no ifs and no buts.
> Even with a negative COUNT.
Any "problems" of `syntax-ppss' in this regard are the problems of
scan_lists plus those of maintaining a cache. No ifs and no buts.
>> Anyway, IIUC this implies that CC mode can't work with `syntax-ppss' at
>> all. If that is true, then `open-paren-in-column-0-is-defun-start' was
>> indeed the last resort that made editing larger files possible.
>
> CC Mode doesn't use syntax-ppss, but I can't see how that's implied by
> anything we've been discussing so far. It does maintain its own caches
> which fulfil the same purpose. For example, there's a syntactic cache
> which treats preprocessor constructs as comments, something syntax-ppss
> can't do.
And how do you invalidate that cache?
> open-..-start being t is a kludge which works for certain types of files
> and situations and not others. It was causing hard to fathom errors in
> CC Mode, particularly C and C++.
I can live with such errors. I can't live with the slowdown.
> Do I take it you're not keen on enhancing find_defun_start in the manner
> I suggested?
What you're asking for is impossible:
(1) You want to base find_defun_start on scan_lists starting at BOB.
This means that you need a function that repeatedly calls
scan_lists, stopping whenever depth reaches zero and remembers that
position, returning the last such position before FROM. Such a
function exists already - it's called `parse-partial-sexp'.
(2) You want to avoid that function call scan_lists repeatedly by
caching previously found positions. Such a function exists already
- it's called `syntax-ppss'.
(3) You want that function to work even if someone changes the syntax
table or disables `before-change-functions' without flushing its
cache. Such a function does not exist and never will.
martin
next prev parent reply other threads:[~2014-06-30 7:55 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.12613.1390467262.10748.bug-gnu-emacs@gnu.org>
2014-01-23 8:53 ` bug#16526: 24.3.50; scroll-conservatively & c-mode regression martin rudalics
2014-01-24 15:45 ` martin rudalics
2014-01-24 20:48 ` Alan Mackenzie
[not found] ` <lbujij$1scv$1@colin.muc.de>
2014-01-25 3:50 ` Juanma Barranquero
2014-01-25 9:23 ` martin rudalics
[not found] ` <52E38286.1050306@gmx.at>
2014-01-25 10:30 ` Eli Zaretskii
2014-01-25 14:58 ` martin rudalics
[not found] ` <52E3D131.2090705@gmx.at>
2014-01-25 16:30 ` Eli Zaretskii
2014-01-25 16:48 ` martin rudalics
2014-01-25 17:29 ` Eli Zaretskii
2014-01-25 18:25 ` martin rudalics
[not found] ` <52E4019C.5080905@gmx.at>
2014-01-25 18:31 ` Eli Zaretskii
2014-01-25 18:40 ` Eli Zaretskii
2014-01-26 11:20 ` martin rudalics
[not found] ` <52E4EF61.3050404@gmx.at>
2014-01-26 17:20 ` Eli Zaretskii
2014-01-26 20:43 ` Alan Mackenzie
2014-01-27 8:21 ` martin rudalics
[not found] ` <52E61704.6050807@gmx.at>
2014-01-27 14:49 ` Stefan Monnier
[not found] ` <jwvvbx5fq2b.fsf-monnier+emacsbugs@gnu.org>
2014-01-27 17:25 ` martin rudalics
[not found] ` <52E69695.5040703@gmx.at>
2014-01-28 0:16 ` Stefan Monnier
2014-01-29 22:36 ` Alan Mackenzie
[not found] ` <20140129223626.GD3092@acm.acm>
2014-01-30 7:37 ` martin rudalics
2014-01-30 13:47 ` martin rudalics
[not found] ` <52EA57D6.5080403@gmx.at>
2014-01-30 17:15 ` Eli Zaretskii
2014-01-30 18:58 ` martin rudalics
[not found] ` <52EAA0C9.1090000@gmx.at>
2014-02-01 10:41 ` Eli Zaretskii
2014-02-02 13:18 ` martin rudalics
2014-02-02 17:40 ` Alan Mackenzie
[not found] ` <20140202174050.GA5365@acm.acm>
2014-02-02 18:07 ` Eli Zaretskii
2014-02-02 19:20 ` Alan Mackenzie
2014-02-02 20:53 ` Eli Zaretskii
2014-02-05 23:00 ` Alan Mackenzie
2014-02-06 6:01 ` Eli Zaretskii
2014-06-22 16:49 ` Eli Zaretskii
2014-06-22 19:32 ` Alan Mackenzie
2014-06-22 20:04 ` Eli Zaretskii
2014-06-25 21:32 ` Alan Mackenzie
2014-06-26 2:51 ` Stefan Monnier
2014-06-27 20:34 ` Alan Mackenzie
2014-06-27 22:33 ` Stefan Monnier
2014-06-27 22:54 ` Stefan Monnier
[not found] ` <jwv8uoim0bm.fsf-monnier+emacsbugs@gnu.org>
2014-06-28 13:00 ` Alan Mackenzie
2014-06-28 14:00 ` martin rudalics
2014-06-28 14:34 ` Stefan Monnier
[not found] ` <53AECA88.7010401@gmx.at>
2014-06-28 14:55 ` Alan Mackenzie
2014-06-28 15:12 ` Eli Zaretskii
2014-06-28 16:30 ` Alan Mackenzie
2014-06-29 8:44 ` martin rudalics
2014-06-29 9:17 ` Alan Mackenzie
2014-06-29 10:06 ` martin rudalics
[not found] ` <53AFE536.7010407@gmx.at>
2014-06-29 12:48 ` Alan Mackenzie
2014-06-29 14:18 ` martin rudalics
2014-06-29 14:41 ` Alan Mackenzie
[not found] ` <20140629144151.GD2948@acm.acm>
2014-06-29 16:01 ` martin rudalics
[not found] ` <53B03876.9070307@gmx.at>
2014-06-29 17:49 ` Alan Mackenzie
2014-06-30 7:55 ` martin rudalics [this message]
2014-06-30 13:48 ` Stefan Monnier
[not found] ` <53B117D6.1050306@gmx.at>
2014-07-02 20:05 ` Alan Mackenzie
[not found] ` <20140702200522.GB3823@acm.acm>
2014-07-03 1:57 ` Stefan Monnier
2014-07-03 8:40 ` martin rudalics
[not found] ` <jwv61jf2owy.fsf-monnier+emacsbugs@gnu.org>
2014-07-03 14:59 ` Stefan Monnier
2014-07-04 18:27 ` Alan Mackenzie
2014-07-04 19:11 ` Stefan Monnier
2014-07-04 19:43 ` Stefan Monnier
2014-07-05 2:23 ` Stefan Monnier
2014-07-06 13:48 ` Alan Mackenzie
2014-07-07 1:52 ` Stefan Monnier
2014-07-07 7:07 ` martin rudalics
[not found] ` <jwvsimevsvz.fsf-monnier+emacsbugs@gnu.org>
2014-07-07 7:07 ` martin rudalics
2014-07-05 20:25 ` Alan Mackenzie
2014-07-05 23:06 ` Stefan Monnier
2014-07-04 19:29 ` Alan Mackenzie
2014-07-05 1:52 ` Stefan Monnier
2014-07-05 7:47 ` Alan Mackenzie
2014-06-29 22:14 ` Stefan Monnier
[not found] ` <jwvionjjrn7.fsf-monnier+emacsbugs@gnu.org>
2014-07-02 18:40 ` Alan Mackenzie
[not found] ` <20140702184013.GA3823@acm.acm>
2014-07-02 19:40 ` Stefan Monnier
[not found] ` <jwvsimpksv1.fsf-monnier+emacsbugs@gnu.org>
2014-06-28 17:33 ` Alan Mackenzie
[not found] ` <20140628173334.GB2632@acm.acm>
2014-06-29 21:39 ` Stefan Monnier
2014-01-29 21:52 ` Alan Mackenzie
2014-01-30 17:16 ` Eli Zaretskii
2014-01-31 20:00 ` Alan Mackenzie
2014-01-31 20:16 ` Eli Zaretskii
2014-01-27 8:20 ` martin rudalics
2014-01-27 16:23 ` Eli Zaretskii
2014-01-27 17:26 ` martin rudalics
2014-01-26 11:19 ` martin rudalics
2014-01-25 20:27 ` bug#16526: 24.3.50; scroll-conservatively & c-mode regression. The purpose of revision 116070 Alan Mackenzie
[not found] ` <20140125202721.GA3630@acm.acm>
2014-01-25 23:02 ` Stefan Monnier
2014-01-26 3:41 ` Eli Zaretskii
2014-01-26 9:54 ` Alan Mackenzie
2014-01-26 16:33 ` Eli Zaretskii
2014-01-26 17:35 ` Eli Zaretskii
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