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Re: cc-mode fontification feels random

From: Daniel Colascione
Subject: Re: cc-mode fontification feels random
Date: Fri, 04 Jun 2021 12:33:25 -0700
User-agent: AquaMail/1.29.2-1810 (build: 102900008)

On June 4, 2021 12:26:47 PM Eli Zaretskii <eliz@gnu.org> wrote:

From: Daniel Colascione <dancol@dancol.org>
CC: <monnier@iro.umontreal.ca>, <joaotavora@gmail.com>, <emacs-devel@gnu.org>
Date: Fri, 04 Jun 2021 12:16:47 -0700

I see no reason for copying, nor for making these tools aware of the
gap.  At least tree-sitter allows the application to provide a
function through which tree-sitter will access the edited text.  It
should be simple to write such a function, because on the C level we
always know where the gap is.

So you propose providing a "char get_buffer_char(size_t POS)" function?
That *is* copying If you run that over all values of POS, all you've done
is make a slow and shitty memcpy.

What do you think tree-sitter does with the fast copy you hand to it?
doesn't it walk it one character at a time?

And if you studied the tree-sitter's internals, and it uses
get_buffer_char as a means of copying text into its own buffer, then
perhaps we could ask tree-sitter developers to avoid the copy and use
the text directly.

Teaching TS to use a generic cursor interface would be great.

So you want to amortize the call over several characters? Okay. Now you've
reinvented buffer-substring.

buffer-substring is not just a copy of a chunk of text, it's much

The variant without text properties doesn't do much.

Even if eventually we need to use a memory copy, that'll run
circles around buffer-substring, and will avoid triggering GC.

Sure. I'm not opposed to adding an API that's basically a more efficient buffer substring for C callers. I'm just pointing out that the idea of giving TS "direct access" to a buffer without any copy at all doesn't make a lot of sense.

Because any kind of "access" to the buffer that doesn't expose the gap is
going to be a copy anyway.

The regexp routines aren't.

The regexp routines have Emacs specific knowledge. My argument doesn't apply to code we can customize for Emacs.

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