CSS parser: selectors and declarations #39

Description#

Implement a CSS parser in the css crate that consumes tokens from the CSS tokenizer and produces a structured stylesheet (CSSOM). Follow CSS Syntax Module Level 3 (§5 Parsing).

Acceptance Criteria#

• Parse stylesheet into a list of rules, where each rule has:
  • A selector list (comma-separated selectors)
  • A declaration block (property-value pairs)
• Selector parsing — support these selector types:
  • Type selectors: div, p, h1
  • Universal selector: *
  • Class selectors: .classname
  • ID selectors: #idname
  • Attribute selectors: [attr], [attr=value], [attr~=value], [attr|=value], [attr^=value], [attr$=value], [attr*=value]
  • Combinators: descendant (space), child (>), adjacent sibling (+), general sibling (~)
  • Compound selectors: div.class#id
  • Selector lists: h1, h2, h3
  • Pseudo-classes (store as name, matching is in style crate): :hover, :first-child, :last-child, etc.
• Declaration parsing:
  • Property name and value pairs separated by :
  • Values as a list of component values (tokens)
  • !important flag
  • Graceful error recovery: skip invalid declarations, don't abort the rule
• @-rules (basic):
  • @media (parse the prelude; nested rules)
  • @import (parse URL string)
• Represent the parsed stylesheet as a Rust data structure (Vec of rules)
• Write tests for selector parsing, declaration parsing, error recovery, @-rules

Dependencies#

• CSS tokenizer (previous issue)

Implementation Notes#

• No external dependencies
• Parse <style> element content and inline style="" attribute values
• Error recovery is important: real-world CSS has errors, parser must not panic