Re: Call for volunteers: add tree-sitter support to major modes

[Yuan Fu]

On Oct 17, 2022, at 8:24 PM, Po Lu <luangruo@yahoo.com> wrote:

Alan Mackenzie <acm@muc.de> writes:

Generally, that the replacement of CC Mode's engine with tree-sitter is
a good idea; CC Mode as it currently is is too much work to maintain,
and in the long run is unsustainable.

At the same time, I have no idea how good tree-sitter's grammars for CC
Mode's modes are.  If I understand rightly, a call to TS requires start
and end buffer positions to be calculated by Emacs rather than TS
itself.  This might reduce some of the expected speed gain.

I would like to keep all of CC Mode's user features in the new mode, if
at all possible.  I don't know how easy it will be, for example, to keep
CC Mode's indentation styles working in the new mode.

I can't honestly see myself as able to integrate tree-sitter into CC
Mode in the short time before the planned pre-test of Emacs 29.  I think
we should take up the offer made by João Paulo Labegalini de Carvalho
<jaopaulolc@gmail.com> on 2020-10-11 to work on C Mode and possibly C++
Mode.

I'm afraid I've only read a small part of this thread on emacs-devel, so
there's likely quite a bit of relevant stuff I've missed.

Could someone please tell me how well tree-sitter supports pre-standard
C with liberal (and sometimes non-standard) use of the C language?  I'm
talking about code that looks like this:

MACRO_USED_TO_DEFINE_SPECIAL_FUNCTIONS (function_name, cells, transform)
    some_kind_of_ptr cells;
    another_kind_of_ptr *transform;
{
 extern maybe_tls (int) errno;
 extern caddr_t bar (_P (another_kind_of_ptr, ...));
 int rc;

 BEGIN_A_KIND_OF_SECTION ({
     ENTRY (dx, dy, shx, shy)
float dx, dy, shx, shy;

     if (!bar (other_function (dx, dy, shx, shy),
etc, etc, etc))
die ("bar", sys_errlist[errno]);
   }, register float, section_name);

 rc = more_code_here (&section_name_desc, etc);
 return rc;
}

I don't doubt that tree-sitter is good at parsing newer languages like
Typescript, but does it support C all that well?

A quick side-by-side comparison of a primitive tree-sitter font-lock I wrote vs c-mode:

Tree-sitter:

C-mode:

Yuan