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

[Yuan Fu]

> On Feb 4, 2023, at 10:01 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Sat, 4 Feb 2023 15:38:17 -0800
>> Cc: Bug Report Emacs <bug-gnu-emacs@gnu.org>,
>> theo@thornhill.no
>> 
>>> treesit-font-lock-recompute-features is a non-interactive function, so
>>> mentioning it in the user manual is generally inappropriate.  Users
>>> are unlikely to add features that aren't already defined in the mode's
>>> font-lock setup.
>>> 
>>> This function and its use in these situations are described in the
>>> ELisp manual, where I think it belongs.
>>> 
>>> As for the fact that changing treesit-font-lock-feature-list directly
>>> doesn't have any effect, that is already in the doc string.  I'm not
>>> opposed to mentioning that in the manual as well, but I see no problem
>>> with what we have.
>> 
>> I see. Sounds good to me. I meant enabling/disabling features when I say 
>> “adding/removing” features. Does that make anything different?
> 
> Yes, that's how I understood what you were saying: changing the list
> of features enabled/disabled by specific levels.  This is not a
> user-level thing, so describing it in the ELisp manual is good enough,
> I think.  (If it turns out users want to do this kind of thing too
> often, it probably means our design of the user-facing features is
> sub-optimal and should be improved.)

I see, my description and the documentation is still not clear enough, I’m 
afraid. treesit-font-lock-recompute-feature does not add/remove features that 
belongs to a level. The design is that, the user uses decoration level to set 
the rough level, which enables a set of features, then use 
treesit-font-lock-recompute-feature to do more fine-grained control by 
additionally enabling/disabling features. 

For example in c-ts-mode, if I set the decoration level to 2, I’d have these 
features: comment, definition, keyword, preprocessor, string, type. If I also 
want the assignment features, which is in level 3, but don’t want other 
features in level 3, I would use treesit-font-lock-recompute-feature to enable 
that feature. Similarly, I can use treesit-font-lock-recompute-feature to 
disable the preprocessor which is at level 2, without affecting other features 
status.


Yuan