bug#61302: 29.0.60; rust-ts-mode does not show function-invocation on field-properties

[Dmitry Gutov <dgutov@yandex.ru>]

On 13/02/2023 16:39, Randy Taylor wrote:

>>
>>From what I can tell, neither of them is perfect yet, but they both get some things right:
>>
>>    rust-ts-mode: function invocations :)
>>    rust-ts-mode handles constants better (also escape-sequences, but not seen in this sample)
>>    rust-mode: consistently fontify annotations (notice they are missing in rust-ts-mode, line 12 and 14). Also rust-mode use font-lock-preprocessor-face, which I think as a more appropriate face for this kind of syntax, than font-lock-constant-face (used in rust-ts-mode).
>>    rust-mode: is able to handle nested macro-invocations. See line 42 and 44 above. From what I can tell, this seems to be due to a short-coming in the tree-sitter grammar for rust, and we may be able to fix it upstream, instead of monkey-patch things based on regexp's in rust-ts-mode
>>
>>As for things which are less great in rust-ts-mode:
>>
>>    some code does not seem to get fontified at all (types, keywords, etc). Line 14-17.
> 
> Did you look at that with treesit-explore-mode?
> It's inside a macro invocation which mostly consists of token_trees.
> Not much helpful stuff for us to go on to highlight.

Depending on the progress in improving the grammar, we could choose to 
add some ad-hoc Lisp based fontification to macro calls (using something 
similar to what rust-mode already does, I guess).

There's no hurry for that, though. Certainly not before Emacs 29 is out.

>>    it seems to fontify all variables using font-lock-variable-name-face all over, regardless of it is a declaration or not. I realize this is not 100% consistent throughout the Emacs-verse, but I know other -ts-modes have aimed for declaration only, and so does rust-mode from MELPA too (although with some consistency-issues) which this would be replacing.
> 
> Because that's what the variable feature is supposed to do, same as the 
> function feature.
> Perhaps rust-ts-mode's definition feature can be augmented to support 
> that

That should already work. Either try treesit-font-lock-level=3, or use 
level 4 but follow it with disabling the 'variable' feature, and you'll 
see variable bindings highlighted. In function parameters and 
let/for/match expressions.

> (and also note it's missing an assignment feature that some other 
> modes have).

I didn't bother with assignments for now (in the absence of feature 
requests), but they should be even easier to add.

Overall, I would recommend to drop the 'variable' feature as it is now 
(sorry for repeating myself), because if we reach the state where 
*everything but* variable references is already highlighted with some 
face, the variable references will stand out automatically (only they 
will be rendered with 'default' face). Adding 
font-lock-variable-name-face drops the distinction between a definition 
and a reference.

But I don't want to force this subject: if you like it enough, no 
problem. The users can disable it manually as well.