• Performance | apps/oxlint/src-js/plugins/selector.ts:50-71
identifierCount() and attributeCount() always shift by IDENTIFIER_COUNT_SHIFT (0) / ATTRIBUTE_COUNT_SHIFT and then mask. The >> IDENTIFIER_COUNT_SHIFT is currently a no-op, and more importantly the helpers are only used for debugAssert checks.

Given this code is in a hot module for perf work, keeping these helpers (and bit extraction) around may add avoidable overhead/indirection unless they’re used elsewhere. If the intent is only to bound-check during debug builds, consider either:

• inlining the bounds checks directly where increments happen, or
• moving these helpers behind a debug-only gate (if your build tooling supports dead-code elimination), or
• removing IDENTIFIER_COUNT_SHIFT entirely (since it’s always 0) and simplifying extraction to specificity & IDENTIFIER_COUNT_MAX.

This will also reduce the chance someone later changes the bit layout but forgets to update the decoding helpers.

• Maintainability | apps/oxlint/src-js/plugins/selector.ts:28-60
  The comment says: “Attribute count takes precedence in sorting, so goes in the higher bits.” With the current layout, specificity comparison sorts primarily by attribute count (higher bits) and then by identifier count (lower bits), which matches the comment.

However, the exit flag is placed above both counts, and is intended to ensure :exit comes after :enter for leaf nodes. That works, but it also means exit-ness always dominates over attribute/identifier specificity when sorting (since it’s the top bit). If you ever have both enter and exit functions in the same merged array (or if this sorting is reused elsewhere), you’re effectively saying “all exits after all enters”, even if an exit selector is more/less specific.

That may be intended, but it’s a semantic change versus the prior approach where the exit flag was also encoded into attributeCount and similarly dominated. The risk is mainly future maintainers expecting specificity-only ordering across enter/exit and getting surprising results.

• Readability | apps/oxlint/src-js/plugins/visitor.ts:286-296
  When name === "*", this code intentionally skips parsing, leaving specificity as either 0 (enter) or EXIT_FLAG (exit). Previously, identifierCount was explicitly set to 0 for *.

This is correct, but it’s now implicit and easier to miss when someone changes the default initialization behavior (especially since the removed comment mentioned default identifier count behavior). Adding a small explicit line or comment would make the behavior less fragile.

• Maintainability | apps/oxlint/src-js/plugins/visitor.ts:287-298
selector.specificity already encodes identifier count, attribute count, and exit flag. Using bitwise-OR to merge (|=) assumes the destination bitfields are zeroed (except possibly the exit flag) and that no bits overlap. This is true for the current control flow, but it’s brittle: if visitProp.specificity ever accumulates other bits (or gets re-used without resetting correctly), OR will silently produce incorrect counts. It also makes the intention slightly unclear: for counts, this is conceptually an addition of disjoint fields.

Given you already assign specificity = EXIT_FLAG for exit fns, you can make this robust and self-documenting by combining via addition while preserving the exit bit explicitly (or by masking the exit bit).

Summary

This change optimizes selector/visitor sorting by packing selector specificity into a single integer.

apps/oxlint/src-js/plugins/selector.ts

• Adds a packed specificity representation combining:
  • identifier count
  • attribute count
  • an exit-flag bit
• Introduces bit layout constants (IDENTIFIER_COUNT_BITS, ATTRIBUTE_COUNT_BITS, shifts, increments) and decoding helpers.
• Replaces Selector.attributeCount/Selector.identifierCount with Selector.specificity and updates analyzeSelector() to increment the packed value (with debugAssert bounds checks).

apps/oxlint/src-js/plugins/visitor.ts

• Replaces VisitProp.attributeCount/VisitProp.identifierCount with VisitProp.specificity.
• Imports EXIT_FLAG and IDENTIFIER_COUNT_INCREMENT from selector.ts and uses them when compiling visitors.
• Simplifies visit fn sorting to a.specificity - b.specificity with selector string as tie-breaker.