Subject: bug#61655: [Tree sitter] [Feature Request] font-lock function calls, definitions, separately

From: Dmitry Gutov <[email-masked]>
Date: Sat, 25 Feb 2023 04:28:11 +0200

Hi Randy,

Thanks for the reply.

On 25/02/2023 03:06, Randy Taylor wrote:

>> Here's the patch which adds the faces and their uses in all ts modes.
>>
>> Comments welcome from all the interested parties. The patch is mostly
>> straightforward, but there are some changes added as well, where it was
>> needed to differentiate between declarations and references.
>>
>> The important question here, I think, is whether we want to split
>> font-lock-property-faces in two, like I did here.
>>
>> By analogy with the other faces, I think it's going to be useful to
>> differentiate between property definitions and property references. Not
>> many of the languages modes used font-lock-property-face for
>> property/attribute definitions, but some did.
> 
> I'm not sure about the naming of font-lock-variable-ref-face. It's confusing for languages that support actual references like C++ and Rust.

But even there "variable reference" is probably a suitable term for any 
occurrence of a variable other than its definition. While the references 
you're talking about are "value references".

> Maybe the opposite direction is better: font-lock-variable-def-face (or something similar) for definitions (or whatnot), and font-lock-variable-name-face to refer to uses (same goes for property). Or font-lock-variable-use-face. I don't know, naming is hard :).

I, uh, pushed the change before I noticed your email. ^^;

But perhaps we could refine, if there is enough support.

Indeed, I was slightly uneasy about the -ref- names, if only because 
they might seem a little cryptic. Using the name -def-face is something 
I thought about too, but it sounded a bit like the name of a macro.

A bigger problem, though, is that existing themes customize 
font-lock-variable-name-face. So we'd have to create inheritance the 
other way around (for the themes to continue working unchanged). Or we'd 
have to create face alias and use a yet different name for "variable 
references" (or "uses", or whatever we'd call them).

Inheritance "the other way around" would break the usage scenario 1 
below for users of existing themes. Or at least make it more difficult.

> Personally, I don't really see the value in differentiating these for variables. I can understand it a little more for properties. But I guess it doesn't hurt to add if folks want it.

I see two potential uses:

1. Customize treesit-font-lock-level to 4 but 
font-lock-variable-ref-face to copy 'default' (or close to it), to skip 
variable reference highlighting or make it less noticeable.

2. Pattern matching or comparably complex syntax which at a first glance 
may look like variable reference, but actually creates new bindings (or 
vice versa, creates new binding when one wanted to refer to an existing 
value).

Emphasizing the difference can help people, beginners especially [in a 
particular language].