Re: Using incremental parsing in Emacs

[Eli Zaretskii <eliz@gnu.org>]

On January 6, 2020 6:39:02 AM GMT+02:00, HaiJun Zhang <netjune@outlook.com> wrote:
> Could someone explain how the jit-lock in Emacs works in the following
> case?
> 
> 1. emacs -Q
> 2. open the attachment file and goto end of buffer
> 3. M-x desktop-save and quit emacs
> 4. emacs -Q
> 5. M-x desktop-read
> 
> I see the buffer is fontified correctly. Does it parse the whole
> buffer?
> 
> 
> 在 2020年1月6日 +0800 AM11:42，Eli Zaretskii <eliz@gnu.org>，写道：
> > > From: arthur miller <arthur.miller@live.com>
> > > CC: "monnier@iro.umontreal.ca" <monnier@iro.umontreal.ca>,
> "alan@idiocy.org"
> > > <alan@idiocy.org>, "emacs-devel@gnu.org" <emacs-devel@gnu.org>
> > > Date: Sun, 5 Jan 2020 20:28:43 +0000
> > >
> > > When I said batch-processing I ment processing a file or chunk of
> buffer (region) just before it is to be
> > > displayed to a user. Same for other "insertions" from macro
> expansions or similar.
> >
> > Then we always do "batch processing", because the display engine has
> > no good idea what exactly changed in the buffer. So it always
> > processes some minimal chunk of text that it can prove to itself
> that
> > the changes were all inside that chunk.
> >
> > > I also don't think teee-sitter is needed for syntax coloring.
> Tree-sitter seems to be very expensive regex engine
> > > in that case.
> >
> > They claim to be less expensive than regexp-based coloring,
> especially
> > with very long lines.
> >

We never parse the whole buffer, only its chunk that is slightly larger than what would be actually displayed in a window.

This works by the display engine calling the fontification-functions for the buffer text it is about to display, whenever it finds a chunk of text whose 'fontified' text property is nil.