bug#66732: tree-sitter fontification doesn't update multi-line syntax reliably

[Dmitry Gutov]

On 19/12/2023 14:41, Eli Zaretskii wrote:
> > From: Stefan Monnier<monnier@iro.umontreal.ca>
> > Cc: Dmitry Gutov<dmitry@gutov.dev>,66732@debbugs.gnu.org,
> >    dominik@honnef.co,casouri@gmail.com
> > Date: Mon, 18 Dec 2023 22:40:59 -0500
> >
> > > > It seems like in our scenario the region does not get re-rendered even
> > > > when some of the faces changed in there.
> > > Can't happen.
> > I think Dmitry is talking about the case where the faces were change
> > after the text was rendered (but before the end of the redisplay cycle).
> >
> > I.e. the redisplay starts, renders up to position POS, then calls
> > jit-lock because `fonfitied` is nil, and jit-lock modifies faces of text
> > *before*  POS.
> This can only happen if a function called from jit-lock doesn't comply
> to the protocol wrt such changes, right?

We have a protocol: font-lock-extend-region-functions, but it's not 
working well enough due to the aforementioned problem.

> Because otherwise the
> modified region would have been re-rendered on the next redisplay
> cycle at the latest.

That does indeed happen, but seems too late from the user's POV.