Re: cc-mode fontification feels random

[Daniel Colascione]

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
> more.

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.