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Re: tree-sitter: conceptional problem solvable at Emacs' level?

From: Ergus
Subject: Re: tree-sitter: conceptional problem solvable at Emacs' level?
Date: Thu, 9 Feb 2023 17:25:59 +0100


Probably I a saying the obvious, but, did you tried to share this in the
treesit syntax repository issues?


Maybe they could give a native better solution... and fix it there, so
we won't need to reinvennt the wheel.


On Thu, Feb 09, 2023 at 12:09:10AM -0800, Holger Schurig wrote:
Hi, I run branch emacs-29 since some time with great success. And now I
wanted to test out tree-sitter and c++-test-mode. Unfortunately, I
stumbled into some conceptional problems and wonder if this is actually
solvable by Emacs, or if some would need a completely new grammar.

The issue is: tree-sitter doesn't work well with C macros.

I program a lot in C++/Qt. So let's look at this (valid) C++ program:

#include <QObject>

class Test : public QObject
       Test() : QObject() {};
public slots:
       void someSlot() {};

If have the libraries installed (e.g. qtbase5-dev on Debian), you can
compile this perfectly.

However, tree-sitter produces a garbage syntax tree:

- contain some bitfield node (which isn't really there)
- contains an error node (despite the code being compilable)

And as a result, BOTH the indentation and the font-locking is wrong.

Would I need to create a tree-sitter grammar in JavaScript that
understands this macro-enhanced C++?   That would be quite difficult.
Or will there be a method to add some kind of tiny-preprocessor to
c++-ts-mode, so that it can substitute "Q_OBJECT", "signals" and "slots"
with nothing before handing things over to tree-sitter?

In comparison, I could teach the old cc-mode about this macro-enriched
C++ just with

 (c-add-style "qt-gnu"
              '("gnu" (c-access-key .
              slots\\|protected slots\\|private slots\\):")))

I guess that a lot of C and C++ programs use macros. And if there is no
simple way to aid tree-sitter in understanding this, then I fear
tree-sitter enhanced modes will often be unusable on them.

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