bug#64818: 30.0.50; c++-ts-mode highlight does not work

[Eli Zaretskii]

> Date: Mon, 24 Jul 2023 18:40:44 +0200
> From: Theodor Thornhill <theo@thornhill.no>
> 
> >> Yep, nullptr was changed from named node to unnamed node last week [0].
> >> 
> >> I think we can live without a compat change and only target the node
> >> as a normal keyword. I'll commit the fix if it is simple enough (the
> >> simplest is just to remove the node altogether),
> >> otherwise I'll send a patch for review. Sounds ok?
> >
> >I'd prefer to see the patch.  Also, can you tell more about the effect
> >of the change you propose ("remove the node")?
> >
> 
> In this case it will only make the symbol "nullptr" get no font locking.

That's probably good enough.  And CC Mode doesn't fontify it, either.

Can you show the patch?

> >More generally, I'm a bit worried by such incompatible changes in the
> >grammar libraries.  The developers must understand that they break
> >users of tree-sitter, right?  So why are they making such incompatible
> >changes?  And how do other editors cope with such changes, for example
> >this one?
> 
> An example from nvim-treesitter: 
> https://github.com/nvim-treesitter/nvim-treesitter/commit/823e67a1c9452075ec7f01e7aa05ac6e7b41fb1e
> 
> It seems most, if not all implementations use some sort of lockfile, where 
> commits are frozen according to the current support. The consensus seems to 
> be to do what I proposed some mails ago: show the last known commit the 
> current file supports, and enable that one to be installed automatically.

I'm not sure how we would maintain this data.  Emacs is a large
project, and people come and go at will and without further notice.
We don't have people who will reliably track the development of the
grammar libraries and record the commits somewhere.  We'd basically
need this when a release is being tarred, and for that it should be
recorded somewhere in advance.

> >I'm asking these questions because perhaps we are doing something we
> >shouldn't, or not doing something we should.  I don't think we can
> >tell our users to use only a specific commit from the grammar
> >libraries' repositories: a significant portion of Emacs users tend to
> >switch to a new version many moons after the release (e.g., I see
> >reports from people who only now upgrade from Emacs 27 to Emacs 28,
> >more than a year since Emacs 28 was released).  So a grammar library
> >which was the current one on the release date will be hopelessly
> >outdated by the time some users will switch to that Emacs version.
> >
> >So we must look for some more robust way, if it exists.
> 
> I agree, but I'm not sure what that looks like.

What about catching errors inside treesit.c or treesit.el, so that the
features that disappeared and queries that fail don't fail the entire
font-lock?  Would that work, or at least make Emacs more robust in the
face of such changes?

Yuan, WDYT?

(This more robust approach is certainly not for Emacs 29.1, even if we
agree that it's a good idea.)