bug#65885: Acknowledgement (29.1.50; wrong behaviour of treesit-beginning-of-defun in c++-ts-mode)

[Eli Zaretskii]

> From: Yang Yingchao <yang.yingchao@qq.com>
> Date: Wed, 13 Sep 2023 08:41:27 +0800
> 
> >>> Date: Tue, 12 Sep 2023 12:41:32 +0800
> >>> From:  Yang Yingchao via "Bug reports for GNU Emacs,
> >>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> >>>
> >>> It seams that there is an issue with the behavior of 
> >>> `treesit-beginning-of-defun` function in
> >>> `c++-ts-mode` when there are static variables present in the source code. 
> >>> For instance, in the
> >>> provided code snippet, if the cursor is initially placed on the line 
> >>> containing `int b`, and the
> >>> "C-M-a" is pressed, the cursor is positioned on line 4 instead of line 1 
> >>> where the beginning of
> >>> the function is located.
> >>>
> >>> ,----
> >>> | void func               // c-ts-mode: treesit-beginning-of-defun stops 
> >>> in this line,   RIGHT
> >>> | {
> >>> |   char * msg;
> >>> |   static int a; // c++-ts-mode: treesit-beginning-of-defun stops in 
> >>> this line, WRONG
> >>> |   int b;        // PUT CUSOR HERE
> >>> | }
> >>> `----
> >>>
> >>> it works in c-ts-mode works normally.
> >>
> >> If you want c++-ts-mode to work like c-ts-mode, set
> >> treesit-defun-tactic to 'top-level'.  By default, we try to support
> >> nested defuns in C++, but not in C.
> >
> >
> > I apologize, but I realized that I have already asked this question before.
> >
> > However, setting 'treesit-defun-tactic' to 'top-level' could cause other
> > issues, as seen in the following snippets:
> >
> >
> > ,----
> > | class Name {
> > | public:
> > |   Name()
> > |   {
> > |     // cursor here
> > |   }
> > |
> > |   void func()
> > |   {
> > |     static int a;
> > |   }
> > |
> > | };
> > `----
> >
> > Suppose the cursor is in line 5, and "C-M-a" is pressed:
> >
> > - In 'c++-mode', the cursor will be moved to the start of the function 
> > 'Name()', which is the expected behavior.
> > - In 'c++-ts-mode':
> >   - With 'treesit-defun-tactic' set to 'nested', it behaves the same as in 
> > 'c++-mode'.
> >   - With 'treesit-defun-tactic' set to 'top-level', the cursor is moved to 
> > the beginning of the class, i.e., line 1.
> >
> > Is it possible to make 'c++-ts-mode' behave the same as in 'c++-mode'?
> >
> > Regards.
> 
> Maybe I'm wrong, but I would like to suggest reconsidering the solution to 
> the 'begging-of-defun' issue related to the static *variable*. It feels 
> strange to me to fix this issue by changing the 'treesit-defun-tactic', which 
> is meant to apply to a *function* literally...

Yuan, any ideas or suggestions?