review: XPath 1.0 evaluator (mirror of upstream #2305)#2
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Ports the capybara-lightpanda XPath 1.0 polyfill into Lightpanda. Exposes the WHATWG Document.evaluate / XPathResult / XPathEvaluator / XPathExpression surface and routes CDP DOM.performSearch XPath queries through the new evaluator. The capybara-lightpanda gem can drop its ~700-line JS polyfill in the next release. New module src/browser/xpath/ (Tokenizer, Parser, Ast, Evaluator, Functions, Result). New webapi types XPathResult, XPathExpression, XPathEvaluator. Coverage and stubs match the polyfill 1:1 — see capybara-lightpanda/XPATH_COMPLIANCE.md for the full spec. Tests: 91-case conformance + result-API + evaluator-API + CDP fixtures, plus the engine's Zig unit suite (601/601 pass).
The Parser borrows string slices from its input for AST literals, names, and var refs. Without duping, the AST holds slices into the JS call_arena, which is reset when the top-level call returns — every subsequent evaluate() of a cached XPathExpression would dereference freed memory.
A bare indexOf("::") matched CSS pseudo-elements (a::before) and
attribute values containing '::' ([data-x="x::y"]), misrouting them
to the XPath evaluator. Require an axis-name shape ([a-zA-Z-])
immediately before '::' so only real axis specifiers like
descendant::p are dispatched to XPath.
The attribute axis was calling Entry.toAttribute on every visit, materializing fresh *Attribute structs (plus duped name/value strings) into page-lifetime storage. Repeated XPath queries — the Capybara/ Selenium polling pattern this PR targets — accumulated unbounded copies for the same DOM entries. Route through frame._attribute_lookup so each Entry resolves to a single cached *Attribute, matching List.getAttribute and NamedNodeMap.getAtIndex.
Per XPath 1.0 §5.7, the data model has no CDATASection node — CDATA content is part of the text node value. The text() node test was only matching DOM nodeType 3 (Text), silently excluding CDATA sections (nodeType 4) parsed via DOMParser/XMLDocument and inline foreign content like SVG with embedded scripts.
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Self-PR opened solely as the host for
/ultrareviewruns against the XPath 1.0 evaluator changes.The real review and merge target is upstream lightpanda-io#2305 — please direct comments there.
This PR will be closed (not merged) once Ultrareview's run completes.