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From: Alan Mackenzie <acm@muc.de>
To: Eli Zaretskii <eliz@gnu.org>
Cc: rudalics@gmx.at, dancol@dancol.org, monnier@iro.umontreal.ca,
	rms@gnu.org, emacs-devel@gnu.org
Subject: Re: cc-mode fontification feels random
Date: Thu, 10 Jun 2021 16:46:11 +0000	[thread overview]
Message-ID: <YMJB08DPbQ2Dj7wv@ACM> (raw)
In-Reply-To: <83k0n2cjg5.fsf@gnu.org>

Hello, Eli.

On Thu, Jun 10, 2021 at 09:39:06 +0300, Eli Zaretskii wrote:
> > Date: Wed, 9 Jun 2021 21:03:03 +0000
> > Cc: dancol@dancol.org, monnier@iro.umontreal.ca, rudalics@gmx.at,
> >   emacs-devel@gnu.org, rms@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > > That's why we had (and still have) font-lock-maximum-decoration: so
> > > that users could control the tradeoff.  Unfortunately, support for
> > > that variable is all but absent nowadays, because of the widespread
> > > mistaken assumption that font-lock is fast enough in all modes.

> > That variable is still supported by CC Mode (with the exception of AWK
> > Mode, where it surely is not needed).

> Does it make a difference, performance-wise?  If not (which is what
> ISTR), then that variable isn't really "supported", because supporting
> it means that different values of it cause tangible differences in
> performance.

Yes, it does make a difference.  On my machine, the times to scroll
through xdisp.c with my favourite benchmark for
font-lock-maximum-decoration set to 3, 2, 1 are 23s, 7.5s, 5.5s.

> > Another possibility would be to replace accurate auxiliary functionality
> > with rough and ready facilities.  In a scroll through xdisp.c, fontifying
> > as we go, the following three functions are taking around 30% of the
> > run-time:

> > (i) c-bs-at-toplevel-p, which determines whether or not a brace is at the
> >   top level.
> > (ii) c-determine-limit, c-determine-+ve-limit, which determine search
> >   limits approximately ARG non-literal characters before or after point.

> > By replacing these accurate functions with rough ones, the fontification
> > would be right most of the time, but a mess at other times (for example,
> > when there are big comments near point).  (i) is more important for C++
> > that C, but still makes a difference in C.

> > If we were to try this, I think a user toggle would be needed.

> How about making font-lock-maximum-decoration control that as well?

Maybe.  It seems, though, that f-l-max-decoration is primarily about the
degree of fontification applied, not its accuracy.

> > > > "Shouldn't try to guess" means taking a great deal of
> > > > font-lock-type-faces out of CC Mode.  I don't honestly think the end
> > > > result would be any better than what we have at the moment.

> > > You don't think it will be better for what reason?

> > Because many users will still want at least the basic types (int, double,
> > unsigned long, ....) fontified

> I'm not sure.  Can you explain why would I care too much about the
> basic types (or types in general) standing out?

Well, I care for my own personal use, because the type fontifications
help optically to separate the different parts of a function without
needing to look too hard.  The coloured bits are the variable
declarations, to a zeroth order approximation.  I suspect different users
have very different needs here.  Doesn't RMS run with font lock switched
off (or is that just a rumour)?

> > > If there's no way of fixing a bug without adversely affecting speed,
> > > we should add user options to control those "fixes", so that people
> > > could choose the balance that fits them.

> > I think this would be a bad thing.  There are no (or very few) similar
> > user options in CC Mode at the moment, and an option to fix or not fix a
> > bug seems a strange idea

> It depends on the bug.  If the bug causes Emacs to infloop or work
> very slowly, then sure, no toggle for the fix would make sense.  But I
> was talking about "bugs" that cause inaccurate or incorrect
> fontifications, and those are much "softer".  At least IMO such "bugs"
> are tolerable if they are rare enough, especially if fixing them hurts
> redisplay performance and Emacs responsiveness in general.

> Don't forget that the display code invokes fontifications also when it
> does internal layout calculations whose results are not immediately
> shown (or even not at all).  When that happens, some command not
> directly related to display could be adversely affected.  So one idea
> would be to turn off these expensive parts in those cases.

That would be difficult.  Frequently a bug fix involves extensive code
changes rather than simply a block of code one could put an `if' around.

> > > Once again, a pathological use case should not punish the usual ones;
> > > if the punishment is too harsh, there should be a way to disable the
> > > support for pathological cases for those who never hit them.

> > The punishment is rarely too harsh for a single bug.  But a lot of
> > 2%s, 3%s or 5%s add up over time.  If we were to outlaw a "3% fix",
> > then many bugs would just be unsolvable.

> Once again: what kind of "bugs" are those?

They're not of any particular kind.  Any bug fix could slow CC Mode down
marginally.  Some have been known to speed it up.

> If they only cause imperfect faces, I'm not sure it's unthinkable to
> disable them, given some optional value of a user knob.

Well, I've fixed around 550 bugs in CC Mode in the last 20 years.
Identifying and reversing a subset of these to revert the performance
would be difficult.

> > Do you have fast-but-imprecise-scrolling enabled?

> No.  That's a separate issue, and influences all the modes, even those
> where font-lock is light-weight.

You could set it buffer locally in c-mode-common-hook, for example.  It
won't solve the basic problem, but it might brighten your day up.

-- 
Alan Mackenzie (Nuremberg, Germany).



  reply	other threads:[~2021-06-10 16:46 UTC|newest]

Thread overview: 274+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-04  3:16 cc-mode fontification feels random Daniel Colascione
2021-06-04  6:10 ` Eli Zaretskii
2021-06-04  7:10   ` Theodor Thornhill
2021-06-04 10:08     ` João Távora
2021-06-04 10:39       ` Eli Zaretskii
2021-06-04 10:59         ` Philipp
2021-06-04 11:05           ` João Távora
2021-06-04 11:22             ` Eli Zaretskii
2021-06-04 12:44               ` Dmitry Gutov
2021-06-04 13:46               ` João Távora
2021-06-04 14:11                 ` Eli Zaretskii
2021-06-04 11:18           ` Eli Zaretskii
2021-06-04 16:43       ` Jim Porter
     [not found]         ` <83k0n9l9pv.fsf@gnu.org>
2021-06-04 19:41           ` Jim Porter
2021-06-04 19:53             ` Eli Zaretskii
2021-06-04 20:05               ` Jim Porter
2021-06-04 20:11                 ` Joost Kremers
2021-06-05  6:51                   ` Eli Zaretskii
2021-06-05 10:14                     ` Joost Kremers
2021-06-05 11:31                       ` Eli Zaretskii
2021-06-05 12:12                         ` Joost Kremers
2021-06-05 13:23                     ` Stefan Monnier
2021-06-05 17:08                       ` Óscar Fuentes
2021-06-05 17:31                         ` Stefan Monnier
2021-06-05 17:32                         ` Eli Zaretskii
2021-06-05 18:46                     ` João Távora
2021-06-05  6:41                 ` Eli Zaretskii
2021-06-05  9:32                   ` João Távora
2021-06-05  9:59                     ` Ergus
2021-06-05 11:29                       ` Eli Zaretskii
2021-06-05 11:55                         ` Daniel Colascione
2021-06-05 12:27                           ` Eli Zaretskii
2021-06-05 17:59                             ` Jim Porter
2021-06-05 18:56                               ` Daniel Martín
2021-06-05 12:43                         ` Ergus
2021-06-05 13:59                       ` Remote GUI Emacs really works (was: cc-mode fontification feels random) Óscar Fuentes
2021-06-05 11:25                     ` cc-mode fontification feels random Eli Zaretskii
2021-06-05  9:46                   ` Ergus
2021-06-05 11:27                     ` Eli Zaretskii
2021-06-04 20:14               ` Yuri Khan
2021-06-04 10:25     ` Eli Zaretskii
2021-06-04 10:05   ` Daniel Colascione
2021-06-04 10:22     ` Eli Zaretskii
2021-06-04 10:34       ` João Távora
2021-06-04 10:43         ` Eli Zaretskii
2021-06-04 18:25         ` Stefan Monnier
2021-06-04 18:36           ` Daniel Colascione
2021-06-04 19:11             ` Eli Zaretskii
2021-06-04 19:16               ` Daniel Colascione
2021-06-04 19:26                 ` Eli Zaretskii
2021-06-04 19:33                   ` Daniel Colascione
2021-06-04 19:51                     ` Eli Zaretskii
2021-06-05  0:29             ` Stefan Monnier
2021-06-05  6:32               ` Eli Zaretskii
2021-06-04 19:07           ` Eli Zaretskii
2021-06-04 19:26             ` Daniel Colascione
2021-06-04 19:32               ` Eli Zaretskii
2021-06-04 10:41       ` Eli Zaretskii
2021-06-04 10:42 ` Ergus
2021-06-04 15:54 ` Alan Mackenzie
2021-06-04 18:30   ` Daniel Colascione
2021-06-06 11:37     ` Alan Mackenzie
2021-06-06 11:57       ` Eli Zaretskii
2021-06-06 12:27         ` Alan Mackenzie
2021-06-06 12:44           ` Eli Zaretskii
2021-06-06 14:19             ` Alan Mackenzie
2021-06-06 17:06               ` Eli Zaretskii
2021-06-06 17:44       ` Stefan Monnier
2021-06-06 18:00         ` Eli Zaretskii
2021-06-06 18:18           ` Stefan Monnier
2021-06-06 18:33             ` Daniel Colascione
2021-06-06 20:24               ` Stefan Monnier
2021-06-06 20:27                 ` Daniel Colascione
2021-06-06 20:38                   ` Stefan Monnier
2021-06-06 19:03             ` Eli Zaretskii
2021-06-06 20:28               ` Stefan Monnier
2021-06-07  7:35                 ` martin rudalics
2021-06-07 13:20                   ` Stefan Monnier
2021-06-07 13:37                     ` Eli Zaretskii
2021-06-08  0:06                       ` Daniel Colascione
2021-06-08 15:16                       ` Stefan Monnier
2021-06-07 15:58                     ` martin rudalics
2021-06-08  4:01                     ` Richard Stallman
2021-06-08 15:29                       ` Stefan Monnier
2021-06-08 15:52                         ` Eli Zaretskii
2021-06-08 16:36                           ` Stefan Monnier
2021-06-08 18:11                             ` Daniel Colascione
2021-06-08 18:25                               ` Eli Zaretskii
2021-06-08 18:28                                 ` Daniel Colascione
2021-06-08 18:54                                   ` Eli Zaretskii
2021-06-09 18:22                                 ` Alan Mackenzie
2021-06-09 18:36                                   ` Eli Zaretskii
2021-06-09 18:51                                     ` Daniel Colascione
2021-06-09 19:04                                       ` Eli Zaretskii
2021-06-09 20:07                                       ` chad
2021-06-10  6:43                                         ` Eli Zaretskii
2021-06-09 20:17                                       ` Dmitry Gutov
2021-06-09 21:03                                     ` Alan Mackenzie
2021-06-10  2:21                                       ` Daniel Colascione
2021-06-10  6:55                                         ` Eli Zaretskii
2021-06-10  6:58                                           ` Daniel Colascione
2021-06-10  7:19                                             ` Eli Zaretskii
2021-06-10  6:39                                       ` Eli Zaretskii
2021-06-10 16:46                                         ` Alan Mackenzie [this message]
2021-06-10 17:01                                           ` Eli Zaretskii
2021-06-10 17:07                                             ` Daniel Colascione
2021-06-10 17:22                                               ` Eli Zaretskii
2021-06-10 17:33                                                 ` Daniel Colascione
2021-06-10 17:39                                                   ` Eli Zaretskii
2021-06-10 17:40                                                 ` Óscar Fuentes
2021-06-10 17:44                                                   ` Eli Zaretskii
2021-06-11 16:11                                                 ` Alan Mackenzie
2021-06-11 17:53                                                   ` Eli Zaretskii
2021-06-11 18:02                                                     ` Daniel Colascione
2021-06-11 18:22                                                       ` Eli Zaretskii
2021-06-11 18:28                                                         ` Daniel Colascione
2021-06-11 19:12                                                           ` Alan Mackenzie
2021-06-11 19:23                                                           ` Eli Zaretskii
2021-06-11 18:47                                                         ` Alan Mackenzie
2021-06-11 19:32                                                           ` Eli Zaretskii
2021-06-11 19:46                                                             ` Alan Mackenzie
2021-06-11 19:50                                                               ` Eli Zaretskii
2021-06-11 18:42                                                       ` Stefan Monnier
2021-06-11 19:31                                                         ` Eli Zaretskii
2021-06-11 19:57                                                           ` Stefan Monnier
2021-06-11 23:25                                                             ` Ergus
2021-06-11 23:52                                                               ` Óscar Fuentes
2021-06-12  1:08                                                                 ` Ergus
2021-06-12  3:20                                                                   ` Stefan Monnier
2021-06-12 11:07                                                                     ` Ergus
2021-06-12  6:58                                                                   ` Eli Zaretskii
2021-06-12 11:01                                                                     ` Ergus
2021-06-12 11:25                                                                       ` Eli Zaretskii
2021-06-12 15:04                                                                         ` Ergus
2021-06-12 15:16                                                                           ` Eli Zaretskii
2021-06-12 15:23                                                                             ` Ergus
2021-06-12 15:35                                                                               ` Eli Zaretskii
2021-06-12 14:00                                                                     ` Stefan Monnier
2021-06-12 14:20                                                                       ` Eli Zaretskii
2021-06-12 14:33                                                                         ` Stefan Monnier
2021-06-12 15:06                                                                           ` Eli Zaretskii
2021-06-12 15:46                                                                             ` Stefan Monnier
2021-06-12  6:50                                                                 ` Eli Zaretskii
2021-06-12  5:20                                                               ` Theodor Thornhill
2021-06-12 13:40                                                                 ` Stefan Monnier
2021-06-12 15:56                                                                   ` Theodor Thornhill
2021-06-12 16:59                                                                     ` Ergus
2021-06-12 17:51                                                                       ` Theodor Thornhill
2021-06-12 17:25                                                                     ` Stefan Monnier
2021-06-12 17:53                                                                       ` Theodor Thornhill
2021-06-12 17:54                                                                       ` Ergus
2021-06-12 18:02                                                                       ` Daniel Colascione
2021-06-12 18:39                                                                         ` Ergus
2021-06-12  6:38                                                             ` Eli Zaretskii
2021-06-12 13:44                                                               ` Stefan Monnier
2021-06-12 14:14                                                                 ` Eli Zaretskii
2021-06-11 20:06                                                           ` Alan Mackenzie
2021-06-12  6:44                                                             ` Eli Zaretskii
2021-06-12  8:00                                                               ` Daniel Colascione
2021-06-12  8:08                                                                 ` Eli Zaretskii
2021-06-12  9:31                                                                   ` Alan Mackenzie
2021-06-11 19:48                                                         ` Eli Zaretskii
2021-06-11 18:34                                                     ` Alan Mackenzie
2021-06-10 17:26                                               ` Óscar Fuentes
2021-06-10 17:39                                               ` andrés ramírez
2021-06-10 21:06                                           ` Stefan Monnier
2021-06-11  6:14                                             ` Eli Zaretskii
2021-06-10 15:16                                       ` Ergus
2021-06-10 15:34                                         ` Óscar Fuentes
2021-06-10 19:06                                           ` Ergus
2021-06-10 19:28                                             ` Eli Zaretskii
2021-06-10 21:56                                               ` Ergus
2021-06-10 15:59                                         ` Jim Porter
2021-06-10 21:02                                         ` Stefan Monnier
2021-06-11 20:21                                           ` Ergus
2021-06-11 20:27                                             ` Stefan Monnier
2021-06-11 20:37                                               ` Daniel Colascione
2021-06-11 20:52                                                 ` Stefan Monnier
2021-06-12  6:46                                                   ` Eli Zaretskii
2021-06-12  8:03                                                     ` Daniel Colascione
2021-06-12  8:13                                                       ` Eli Zaretskii
2021-06-12 13:51                                                       ` Stefan Monnier
2021-06-12  8:47                                                   ` Daniele Nicolodi
2021-06-12  8:57                                                     ` tomas
2021-06-12 14:04                                                     ` Stefan Monnier
2021-06-09 19:05                                   ` Daniel Colascione
2021-06-09 19:11                                     ` Eli Zaretskii
2021-06-09 20:20                                     ` Alan Mackenzie
2021-06-09 20:36                                       ` Stefan Monnier
2021-06-10  7:01                                         ` Daniel Colascione
2021-06-10  7:21                                           ` Eli Zaretskii
2021-06-10  2:21                                       ` Daniel Colascione
2021-06-19  9:25                                         ` Alan Mackenzie
2021-06-19 15:24                                           ` Alan Mackenzie
2021-07-09 14:06                                             ` Daniel Colascione
2021-07-11 18:12                                               ` Stephen Leake
2021-07-15 18:13                                                 ` Perry E. Metzger
2021-07-15 22:43                                                   ` Tree Sitter (was Re: cc-mode fontification feels random) Perry E. Metzger
2021-07-19 23:49                                                     ` Stephen Leake
2021-07-20 14:53                                                       ` Perry E. Metzger
2021-07-21  0:04                                                         ` Stephen Leake
2021-07-21  1:28                                                           ` Stefan Monnier
2021-07-21 14:43                                                             ` Perry E. Metzger
2021-07-21 16:21                                                               ` Daniel Colascione
2021-07-21 19:15                                                                 ` Perry E. Metzger
2021-07-22  1:16                                                                   ` Daniel Colascione
2021-07-22 13:18                                                                     ` Perry E. Metzger
2021-07-22 13:49                                                                     ` Yuan Fu
2021-07-24 20:05                                                                     ` [SPAM UNSURE] " Stephen Leake
2021-07-25  0:41                                                                       ` Daniel Colascione
2021-07-26  4:24                                                                         ` [SPAM UNSURE] " Stephen Leake
2021-07-25 18:01                                                                       ` Perry E. Metzger
2021-07-22 14:00                                                           ` Perry E. Metzger
2021-07-24  1:17                                                             ` Richard Stallman
2021-07-25 16:13                                                               ` Stephen Leake
2021-07-25 19:52                                                                 ` Ada (was Re: Tree Sitter) Perry E. Metzger
2021-07-26  5:05                                                                   ` Stephen Leake
2021-07-26  9:42                                                                     ` Stephen Leake
2021-07-26 14:01                                                                       ` Perry E. Metzger
2021-07-26 13:45                                                                     ` Perry E. Metzger
2021-07-27  0:26                                                                   ` Richard Stallman
2021-07-27 12:38                                                                     ` Perry E. Metzger
2021-07-26  2:23                                                                 ` Tree Sitter (was Re: cc-mode fontification feels random) John Yates
2021-07-24 19:59                                                             ` Stephen Leake
2021-07-24 21:21                                                               ` OFF-TOPIC: Ada availability (was: Tree Sitter) Óscar Fuentes
2021-07-25  7:31                                                                 ` tomas
2021-06-08 18:11                             ` cc-mode fontification feels random Eli Zaretskii
2021-06-08 21:25                               ` Stefan Monnier
2021-06-09  3:39                         ` Richard Stallman
2021-06-09  8:34                         ` martin rudalics
2021-06-09 13:14                           ` `open-paren-in-column-0-is-defun-start` (was: cc-mode fontification feels random) Stefan Monnier
2021-06-09 15:15                             ` Yuri Khan
2021-06-09 15:16                               ` Yuri Khan
2021-06-12 17:29                           ` cc-mode fontification feels random João Távora
2021-06-13  8:50                             ` martin rudalics
2021-06-13  9:05                               ` João Távora
2021-06-13  9:39                                 ` martin rudalics
2021-06-13 10:06                                   ` João Távora
2021-06-13 14:52                                     ` martin rudalics
2021-06-13 15:25                                       ` João Távora
2021-06-14  8:29                                         ` martin rudalics
2021-06-14  8:40                                           ` João Távora
2021-06-14  9:00                                             ` martin rudalics
2021-06-14  9:14                                               ` João Távora
2021-06-14 11:28                                           ` Eli Zaretskii
2021-06-14 14:39                                           ` Stefan Monnier
2021-06-15 22:38                                             ` Ergus
2021-06-07 12:08                 ` Eli Zaretskii
2021-06-08 15:22                   ` Stefan Monnier
2021-06-08 15:46                     ` Eli Zaretskii
2021-06-05 20:25   ` Dmitry Gutov
2021-06-06 11:53     ` Alan Mackenzie
2021-06-06 17:08       ` Dmitry Gutov
2021-08-30 18:50 ` [PATCH] " Alan Mackenzie
2021-08-30 19:03   ` Perry E. Metzger
2021-08-30 19:18     ` Alan Mackenzie
2021-08-30 19:25   ` Eli Zaretskii
2021-08-30 19:28     ` Daniel Colascione
2021-08-30 19:37       ` Eli Zaretskii
2021-08-30 20:11       ` Stefan Monnier
2021-08-31 10:54         ` Alan Mackenzie
2021-08-31 13:23           ` Eli Zaretskii
2021-08-31 16:02             ` Alan Mackenzie
2021-08-31 16:21               ` Eli Zaretskii
2021-08-31 16:46                 ` Alan Mackenzie
2021-08-31 17:02                   ` Eli Zaretskii
2021-08-31 18:56           ` Stefan Monnier
2021-08-31 21:17             ` Alan Mackenzie
2021-08-31 21:47               ` Stefan Monnier
2021-10-22 20:13               ` [Committed PATCH] " Alan Mackenzie
2021-10-24 20:18                 ` Alan Mackenzie
2021-08-31 13:18         ` [PATCH] " Eli Zaretskii
2021-08-30 20:03     ` Alan Mackenzie
2021-08-31 11:53       ` Eli Zaretskii

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