WHATWG URL parser (full spec compliance) #56

Phase 6: URL Parser#

Implement the WHATWG URL Standard parser in the url crate (crates/url/src/lib.rs).

Requirements#

• URL record type: scheme, username, password, host, port, path, query, fragment
• URL parsing algorithm per https://url.spec.whatwg.org/#url-parsing
  • State machine with all states: scheme start, scheme, authority, host, port, path, query, fragment
  • Special scheme handling (http, https, ftp, ws, wss, file)
  • Percent-encoding and decoding (UTF-8)
  • IDNA/punycode for internationalized domain names (basic support)
• Host parsing: domain, IPv4, IPv6 address parsing
• URL serialization: serialize back to string form
• Relative URL resolution: resolve relative URLs against a base URL
• Origin: derive origin from URL (scheme, host, port tuple)
• API surface: Url::parse(input), Url::parse_with_base(input, base), accessor methods

Dependencies#

• we-encoding crate (already a dependency in Cargo.toml)

Acceptance Criteria#

• Parse absolute URLs: https://user:pass@example.com:8080/path?q=1#frag
• Parse relative URLs against a base
• IPv4 and IPv6 host parsing
• Percent-encoding/decoding
• Special scheme default ports (http=80, https=443, etc.)
• Serialization round-trips correctly
• Edge cases: empty path, missing components, trailing slashes
• Comprehensive test suite (50+ tests)
• cargo clippy and cargo fmt clean