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WASM bindings around Servo's `selectors` crate, intended to eventually replace Alfa's TypeScript selector parsing and matching in alfa-cascade. Motivated by a nesting bug where desugared `:is()` selectors from `&` rules don't match correctly in the current engine. Milestone 2: ingests a real Alfa DOM via a binary serialization bridge, parses selectors (including :is(), :where(), :has(), & nesting), and matches type/class/id/attribute/descendant/child/ sibling/:root/:nth-child() selectors against real Alfa elements, plus specificity. Cascade integration (Milestone 3) and & nesting resolution (Milestone 4) are not yet started. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Wires the WASM selector engine into alfa-cascade's SelectorMap: candidate matching is delegated to it wherever it can parse the selector, falling back to the existing TypeScript Selector#matches otherwise (currently anything using a Context-dependent pseudo-class, e.g. :hover/:focus-within, since those need Context-state support the engine doesn't have yet). :host/::slotted selectors are unaffected, they already matched through their own matchHost/matchSlotted paths. Also includes the prerequisite work this surfaced: - Fixed :has() matching in the Rust engine: ElementRef::opaque() derived its identity token from a transient stack address rather than the arena index, so the selectors crate's relative-selector anchor check always failed. selector-wasm is now wired into the standard TS project-reference build (packages/tsconfig.json, ts/tsconfig.json, test/tsconfig.json) so alfa-cascade can depend on it normally. - Made SelectorEngine a process-wide singleton with idempotent loadDom(): the compiled WASM module's DOM arena is process-global, but Cascade keeps many documents' cascades alive concurrently, so matching now always (re)asserts the right tree is loaded first. - Fixed alfa-selector's Selector#toString() leaking a literal "of None" into serialized bare :nth-child()/:nth-last-child() selectors, which would otherwise force every such selector to fall back to TS matching unnecessarily. Note: the original motivating nesting bug isn't fixed end-to-end yet. alfa-dom's real-world CSSOM ingestion (native.ts) doesn't capture nested style rules, so a raw `&` selector never reaches the cascade today; only already-desugared selectors do. That's separate alfa-dom work. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Summary
Continues the
alfa-selector-wasmeffort (a Rust/WASM selector engine built on Servo'sselectorscrate, originally motivated by a nesting bug where desugared:is()-wrapped selectors from&rules didn't match correctly).alfa-cascade'sSelectorMap. Candidate matching is delegated to WASM wherever it can parse the selector, falling back to the existing TypeScript matcher otherwise (currently: selectors using a Context-dependent pseudo-class like:hover/:focus-within, since those need Context-state support the engine doesn't have yet).:host/::slottedselectors are untouched.Also includes prerequisite fixes this surfaced:
:has()matching was silently broken in the Rust engine (ElementRef::opaque()derived its identity token from a transient stack address rather than the arena index, so theselectorscrate's relative-selector anchor check always failed).alfa-selector-wasmis now wired into the standard TS project-reference build soalfa-cascadecan depend on it normally.SelectorEngineis now a process-wide singleton with idempotentloadDom(), since the compiled WASM module's DOM arena is process-global butCascadekeeps many documents' cascades alive concurrently.alfa-selector'sSelector#toString()leaked a literal"of None"into serialized bare:nth-child()/:nth-last-child()selectors, which would've forced every such selector to fall back to TS matching unnecessarily.Known gap carried forward: the original motivating nesting bug isn't fixed end-to-end yet.
alfa-dom's real-world CSSOM ingestion (native.ts) doesn't capture nested style rules at all, so a raw&selector never reaches the cascade today — only already-desugared selectors do. That's separatealfa-domwork, tracked outside this PR.Test plan
:has()matching (direct child, deep descendant, sibling combinator, absence, composition with:is())alfa-selector-wasm's Alfa-integrated vitest suite (bridge.spec.tsx)alfa-cascadetest suite, including a new end-to-end test matching a WASM-backed:is()+:has()selector through the fullCascadealfa-selector,alfa-selector-wasm,alfa-cascade,alfa-style,alfa-rules— 2041 tests passing, no type errorsalfa-selectorpatch,alfa-cascadepatch)🤖 Generated with Claude Code