bug: failed to parse :host pseudo class

[jordimarimon]

Did you check existing issues?

• I have read all the tree-sitter docs if it relates to using the parser
• I have searched the existing issues of tree-sitter-css

Tree-Sitter CLI Version, if relevant (output of tree-sitter --version)

No response

Describe the bug

I have installed the latest version of the parser (commit hash: 6a442a3cf461b0ce275339e5afa178693484c927)

When using the :host pseudo class without arguments, I get errors in the parsed tree.

https://developer.mozilla.org/en-US/docs/Web/CSS/:host

Steps To Reproduce/Bad Parse Tree

The following fails to parse:

:host {
    display: block;
}

This is the AST that I get when I use the InspectTree command in neovim:

(stylesheet ; [0, 0] - [3, 0]
  (ERROR ; [0, 0] - [2, 1]
    (class_name) ; [0, 1] - [0, 5]
    (ERROR) ; [1, 4] - [1, 5]
    (class_name) ; [1, 5] - [1, 7]
    (ERROR) ; [1, 7] - [1, 11]
    (ERROR))) ; [1, 13] - [1, 18]

If I write the following:

:host() {
     display: block;
}

It parses correctly.

Expected Behavior/Parse Tree

It's valid to write the :host pseudo class without arguments.

I don't have a lot of knowledge about writing grammars with tree-sitter but I suspect that this line may be the one causing the conflict:

tree-sitter-css/grammar.js

Line 183 in 6a442a3

alias($.pseudo_class_with_selector_arguments, $.arguments),

Repro

:host {
    display: block;
}

[mohamedmansour]

/cc @amaanq , :host is really critical to css spec!

[mohamedmansour]

Hey @jordimarimon are you going to open a PR with your change jordimarimon@2b7ecb8 ? /cc @amaanq

[jordimarimon]

Sorry for the late response @mohamedmansour, I didn't create a pull request because I wasn't quite sure that my approach for fixing the issue would be the best.

What I have done is make optional the arguments in some pseudo classes which may be desirable or not depending if it's a good thing for the grammar to accept more broader inputs.

I don't see it as a bad thing as I'm using treesitter inside neovim and in my case is for syntax highlighting, so I prefer the grammar to accept invalid CSS also, as this way when I'm in the middle of writting something, the AST doesn't have errors and the highlighting looks fine.

If it's okay for the maintainers of this grammar what I have done, I can open a pull request!

[mohamedmansour]

@amaanq CSS :host parameter is more broken than before now, can we merge @jordimarimon PR in? Would love to maybe contribute to this repo as well since treesitter CSS needs better syntax support in Zed @maxbrunsfeld

[mohamedmansour]

@jordimarimon can you please open the PR? And we can see how it goes

[mohamedmansour]

@jordimarimon I tested your change and I am getting error, unless I am loading it wrong

[mohamedmansour]

Ah it does work @jordimarimon I had to run npx tree-sitter generate before npm run install