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From: Alan Mackenzie <acm@muc.de>
To: John Wiegley <jwiegley@gmail.com>
Cc: 22983@debbugs.gnu.org, Philipp Stephani <p.stephani2@gmail.com>,
	Dmitry Gutov <dgutov@yandex.ru>
Subject: bug#22983: syntax-ppss returns wrong result.
Date: Thu, 7 Sep 2017 20:45:02 +0000	[thread overview]
Message-ID: <20170907204502.GC4488@ACM> (raw)
In-Reply-To: <m2vakxxraz.fsf@newartisans.com>

Hello, John.

On Tue, Sep 05, 2017 at 13:28:52 +0100, John Wiegley wrote:
> >>>>> Dmitry Gutov <dgutov@yandex.ru> writes:

> > I'm sure we want to fix design flaws. As long as there is a solid plan that
> > does not swap one flaw for another.

> Can we have a summary of the current proposal(s) on the table? It would help
> to clarify, rather than navigating past discussions. Alan has told me that
> this issue is affecting people and has been outstanding for some time; I'd
> like to get a better idea of its seriousness/scope, and what effect the
> available solutions would have (as Dmitry says, we don't want to replace one
> flaw with another).

First, I think it's worthwhile emphasising what the function purports to
do:

    syntax-ppss is a compiled Lisp function in `syntax.el'.

    (syntax-ppss &optional POS)

    Parse-Partial-Sexp State at POS, defaulting to point.
    The returned value is the same as that of `parse-partial-sexp'
    run from `point-min' to POS except that values at positions 2 and 6
    in the returned list (counting from 0) cannot be relied upon.
    Point is at POS when this function returns.

The solution I propose is to introduce a second cache into syntax-ppss,
and this cache would be used whenever (not (eq (point-min) 1)).
Whenever point-min changes, and isn't 1, this second cached would be
calculated again from scratch.

This proposal has these advantages:

(i) It would make the function deliver what its unchanged doc string
says.  This is important, given that syntax-ppss has been very widely
used within Emacs, and likely by external packages too; these will
typically have assumed the advertised behaviour of the function, without
having tested it in narrowed buffers.

(i) In the case which currently works, namely a non-narrowed buffer,
there would be only a minute slow-down (basically, there would be extra
code to check point-min and select the cache to use).

(ii) The cache for use in a narrowed buffer might well be sufficiently
fast in normal use.  If it is not, it could be enhanced readily.

I think Dmitry also proposed a method of solution some months ago,
though I don't remember in detail what it was.  Dmitry, do you still
think your solution would work?  If so, please elaborate on it.

> -- 
> John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
> http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

-- 
Alan Mackenzie (Nuremberg, Germany).





  reply	other threads:[~2017-09-07 20:45 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-11 15:15 bug#22983: syntax-ppss returns wrong result Alan Mackenzie
2016-03-11 20:31 ` Dmitry Gutov
2016-03-11 21:24   ` Alan Mackenzie
2016-03-11 21:35     ` Dmitry Gutov
2016-03-11 22:15       ` Alan Mackenzie
2016-03-11 22:38         ` Dmitry Gutov
2016-03-13 17:37           ` Stefan Monnier
2016-03-13 18:57             ` Alan Mackenzie
2016-03-14  0:47               ` Dmitry Gutov
2016-03-14  1:04                 ` Drew Adams
2016-04-03 22:55                   ` John Wiegley
2016-03-14  1:49               ` Stefan Monnier
2016-03-13 17:32     ` Stefan Monnier
2016-03-13 18:52 ` Andreas Röhler
2016-03-13 18:56   ` Dmitry Gutov
2016-03-18  0:49 ` Dmitry Gutov
2016-03-19 12:27   ` Alan Mackenzie
2016-03-19 18:47     ` Dmitry Gutov
2016-03-27  0:51       ` John Wiegley
2016-03-27  1:14         ` Dmitry Gutov
2016-04-03 22:58           ` John Wiegley
2016-04-03 23:15             ` Dmitry Gutov
2017-09-02 13:12               ` Eli Zaretskii
2017-09-02 17:40                 ` Alan Mackenzie
2017-09-02 17:53                   ` Eli Zaretskii
2017-09-03 20:44                   ` John Wiegley
2017-09-04 23:34                   ` Dmitry Gutov
2017-09-05  6:57                     ` Andreas Röhler
2017-09-05 12:28                     ` John Wiegley
2017-09-07 20:45                       ` Alan Mackenzie [this message]
2017-09-08 16:04                         ` Andreas Röhler
2017-09-10 18:26                           ` Alan Mackenzie
2017-09-09  9:44                         ` Dmitry Gutov
2017-09-09 10:20                           ` Alan Mackenzie
2017-09-09 12:18                             ` Dmitry Gutov
2017-09-10 11:42                               ` Alan Mackenzie
2017-09-10 11:36                           ` bug#22983: [ Patch ] " Alan Mackenzie
2017-09-10 22:53                             ` Stefan Monnier
2017-09-10 23:36                               ` Dmitry Gutov
2017-09-11 11:10                                 ` Stefan Monnier
2017-09-12  0:11                                   ` Dmitry Gutov
2017-09-12 22:12                                     ` Richard Stallman
2017-09-11 19:42                               ` Alan Mackenzie
2017-09-11 20:20                                 ` Stefan Monnier
2017-09-11  0:11                             ` Dmitry Gutov
2017-09-11 20:12                               ` Alan Mackenzie
2017-09-12  0:24                                 ` Dmitry Gutov
2017-09-17 10:29                                   ` Alan Mackenzie
2017-09-17 23:43                                     ` Dmitry Gutov
2017-09-18 19:08                                       ` Alan Mackenzie
2017-09-19  0:02                                         ` Dmitry Gutov
2017-09-19 20:47                                           ` Alan Mackenzie
2017-09-22 14:09                                             ` Dmitry Gutov
2017-09-24 11:26                                               ` Alan Mackenzie
2017-09-25 23:53                                                 ` Dmitry Gutov
2017-10-01 16:36                                                   ` Alan Mackenzie
2017-10-04 20:07                                                 ` Johan Bockgård
2017-09-17 11:12                             ` Philipp Stephani
2017-09-19 20:50                               ` Alan Mackenzie
2017-09-07 17:56                     ` Alan Mackenzie
2017-09-07 20:36                       ` Dmitry Gutov
2016-03-19 23:16     ` Vitalie Spinu
2016-03-19 23:00   ` Vitalie Spinu
2016-03-19 23:20     ` Dmitry Gutov
     [not found] ` <mailman.7307.1457709188.843.bug-gnu-emacs@gnu.org>
2017-10-01 16:31   ` Alan Mackenzie

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