GNU bug report logs - #65885
29.1.50; wrong behaviour of treesit-beginning-of-defun in c++-ts-mode

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From: Yang Yingchao <yang.yingchao <at> qq.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 65885 <at> debbugs.gnu.org
Subject: bug#65885: Acknowledgement (29.1.50; wrong behaviour of treesit-beginning-of-defun in c++-ts-mode)
Date: Wed, 13 Sep 2023 08:03:48 +0800

[Message part 1 (text/plain, inline)]

>> 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 <at> 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.

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