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

[Holger Schurig <holgerschurig@gmail.com>]

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
{
        Q_OBJECT
public:
        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 .
                       "\\<\\(signals\\|public\\|protected\\|private\\|public
               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.