Crest

Overview

Crest is a Rust library for working with CSS selectors and stylesheets. It provides tools to parse and validate CSS syntax, match selectors against custom DOM-like structures, and apply styles programmatically.

Status

Crest is nearing alpha, and is able to parse any css style rules but unable to parse at-rules. It can also only validate a VERY limited subset of the standard style properties, and some Peacock-specific ones. It's already fairly fast, with planned changes to validation that should make it much faster.

Features

• CSS Parsing: Parse and validate CSS strings, including selectors and stylesheets.
• Selector Matching: Match parsed selectors against types implementing the DomElement trait.
• Custom DOM Support: Easily integrate with your own DOM-like structures by implementing the DomElement trait.

Roadmap

• Expand benchmark coverage.
• Document simple use cases.
• Define the DomElement trait.
• Add detailed examples for the DomElement trait.
• Document advanced use cases.

Quickstart

Installation

Crest is not yet available on crates.io. To use it, include it as a dependency using a git repository:

[dependencies]
peacock-crest = { git = "https://github.com/nucleus-labs/Crest/", rev = "<rev>" }

Selector Parsing

Crest uses Pest to generate parsers for CSS selectors and for the full CSS syntax. Here's how you can parse a selector string:

use peacock_crest::{SourceInfo, SelectorNode};

let selector = "div > .example";
let source_info = SourceInfo::new(selector);
let parsed_selector = SelectorNode::from_source(source_info).expect("Failed to read css");

println!("Parsed selector: {}", parsed_selector);

Stylesheet Parsing

You can also parse full CSS stylesheets:

use peacock_crest::{SourceInfo, Stylesheet};

let css = "div { color: red; } .example { font-size: 16px; }";
let source_info = SourceInfo::new(css);
let stylesheet = Stylesheet::from_source(source_info).expect("Failed to read css");

println!("Parsed stylesheet:\n{}", stylesheet);

Selector Matching

To match a selector against a custom element, implement the DomElement trait for your type:

// todo

Testing and Validation

Crest currently uses the following to validate Crest's functionality for historical reference and to ensure compatibility with a range of CSS practices:

• acid1
• acid2
• bootstrap 1 (bootstrap2 relies on non-compliance with the standard and as such has been skipped in tests for historical compliance)
• bootstrap 2 (bootstrap2 relies on non-compliance with the standard and as such has been skipped in tests for historical compliance)
• bootstrap 3 (bootstrap2 relies on non-compliance with the standard and as such has been skipped in tests for historical compliance)
• bootstrap 4
• bootstrap 5

To run them, use:

cargo test

Benchmarks

Performance benchmarks are available in the benches directory. To run them, use:

cargo bench

Current Results: