bug#62333: 30.0.50; Issue with tree-sitter syntax tree during certain changes

[Dmitry Gutov]

On 25/03/2023 19:40, Eli Zaretskii wrote:
> > Date: Sat, 25 Mar 2023 19:05:13 +0200
> > Cc: wkirschbaum@gmail.com, casouri@gmail.com, 62333@debbugs.gnu.org
> > From: Dmitry Gutov <dgutov@yandex.ru>
> >
> > On 25/03/2023 18:24, Eli Zaretskii wrote:
> > > > From: Dmitry Gutov <dgutov@yandex.ru>
> > > > Cc: "wkirschbaum@gmail.com" <wkirschbaum@gmail.com>,
> > > >         "casouri@gmail.com" <casouri@gmail.com>,
> > > >         "62333@debbugs.gnu.org" <62333@debbugs.gnu.org>
> > > > Date: Sat, 25 Mar 2023 19:03:45 +0300
> > > >
> > > >     But if the mmm framework narrowed the region to the current mode's
> > > >     block, widening will force tree-sitter to parse the whole buffer.
> > > >
> > > >    No, because such a mode mode should already make sure this doesn't
> > > >    happen.
> > > >
> > > > How?
> > >
> > > The same way it makes sure a given parser is used only on the portion
> > > of the buffer where the corresponding language is used.
> >
> > It uses narrowing.
>
> How does that work with features such as font-lock, which do widen?

Using font-lock-dont-widen.

We've had this discussion several times over by now. Should it be 
documented somewhere?

> Anyway, isn't this discussion a bit premature, as no TS mode has been
> used with the mmm framework yet?

There is no reason to assume that: the combinations of modes are just a 
matter of user configuration. And so far it should be working okay.

> Because when they do, I imagine they
> will need to invent some mechanism that is more reliable than
> narrowing.

"They" is me. I'd rather the general mechanism keeps working, or we come 
up with another general mechanism that is a better substitute, before 
breaking this one.

And anyway, I like I mentioned, this will break this common pattern as well:

  (save-restriction
    (narrow-to-region ... some-limit-position)
    (forward-sexp))

I've used it in ruby-syntax-propertize-percent-literal, for example. 
Except with 'forward-list' rather than 'forward-sexp', but others can 
use the latter.