bug#60983: 29.0.60; Tree-sitter user-level control

[Theodor Thornhill via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> I started looking into providing user-level documentation for
> tree-sitter based modes, and bumped into some issues:
>
>  . How does one use treesit-font-lock-level?
>
>    - It is not a customizable user option (unlike
>      font-lock-maximum-decoration), so it cannot be set via
>      customize-variable.  Is there a reason not to make it a
>      defcustom?
>    - It automatically becomes buffer-local when set, and OTOH setting
>      it in a buffer does not produce fontifications according to the
>      level, and neither does setting it in a mode hook.  So the only
>      way to change its value is by using setq-default, which I don't
>      think is the intent?
>    - Should we make the variable a defcustom?
>    - Should it be possible to customize it separately for each mode?
>    - Should we allow to change the level and then call some function
>      to re-fontify the current buffer according to the new level?

I struggled with this too.  I ended up setting it with setq-default,
assuming I was just missing something very simple.  I'm in favor for
either a defcustom or honoring the font-lock-maximum-decoration values,
specifically these settings:

```
If t, use the maximum decoration available.
If a number, use that level of decoration (or if not available the maximum).
```

>
>  . How does one change the indentation style in c-ts-mode?
>
>    - There is a defcustom c-ts-mode-indent-style, but I don't think I
>      see any difference in indentation of new code when I change the
>      value.  What am I missing?
>

(setq c-ts-mode-indent-style 'bsd) then revert-buffer fixes it for me.
It seems you need to reload the file to enable the new style.  Should I
add a command that can be set explicitly as in c-mode?
'c-ts-mode-set-style'?

However, going over it I see there are lots of regressions after the new
bracket-counting code added recently, effectively making the indent
styles pretty broken right now...

For example with bsd style:

Previously:

int
main()
{
  if (x)
  {
      
  }
  else
	{
		
  }
}

now:

int
main()
{
  if (x)
  {
      
    }
  else
	{
		
		}
}



>  . What commands are affected by treesit-defun-tactic?

'treesit--navigate-thing' uses it, so 'beginning-of-defun',
'forward-sentence' etc uses it through 'treesit-beginning-of-thing'.

Theo