perf(parser): reuse cached token kind in delimited-list loops#22841
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## What In `parse_delimited_list` and `parse_delimited_list_into` (`cursor.rs`), the loop already caches `let kind = self.cur_kind();` at the top of each iteration, then re-reads the same token via `if !self.at(separator)` — which expands to `self.token.kind() == separator`. No token mutation (`advance`/`bump`/`next_token`) happens between the cache and the separator check, so `!self.at(separator)` is provably identical to `kind != separator`. This reuses the already-loaded `kind` and avoids re-reading `self.token` once per element of every array literal, object literal, parameter list, and argument list. ## Correctness Semantics-preserving — no change to parse results or diagnostics. - `cargo test -p oxc_parser`: pass - `cargo coverage -- parser`: zero conformance snapshot diff (Test262 / TypeScript / Babel / estree) - `just fmt` + `cargo clippy -p oxc_parser --all-features --all-targets`: clean ## Performance A micro-optimization (removes one in-register/L1 token-field comparison per delimited-list element). Measured via an interleaved A/B against a parse-invariant control (`estree/checker.ts`); combined with the modifier-path change it lands ~0.5–1% on declaration/member-dense files (`binder.ts`), noise-level elsewhere. The main value is making the reuse of the cached `kind` explicit. 🤖 Generated with [Claude Code](https://claude.com/claude-code)
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### 🚀 Features - 9c71f2e ast, codegen, formatter: Add `WithClauseKeyword::as_str` helper and use it (#22791) (camc314) ### 🐛 Bug Fixes - cf5769c parser: Reject TypeScript declarations in single-statement context (#22827) (Boshen) - c360fb6 parser: Reject generators in ambient contexts and overload signatures (TS1221/TS1222) (#22848) (Boshen) - cc60d8d parser: Reject invalid index signature parameter types (TS1268/TS1337) (#22852) (Boshen) - 3d13e29 parser: Reject `declare` in an already-ambient context (TS1038) (#22850) (Boshen) - 5152854 parser: Reject statements in ambient contexts (TS1036) (#22849) (Boshen) - 4f9afc5 parser: Reject `export as namespace` inside a namespace body (TS1316) (#22846) (Boshen) - 2eafea6 parser: Reject function implementations in ambient contexts (TS1183) (#22845) (Boshen) - c645615 parser: Reject incompatible class member modifiers (#22843) (Boshen) - 276b78b parser: Reject module-referencing imports/exports in a namespace body (#22836) (Boshen) - 842ed1c parser: Parse `class implements` with `implements` as the class name (#22801) (Boshen) ### ⚡ Performance - 7e3a567 parser: Reuse cached token kind in delimited-list loops (#22841) (Boshen) - 9e741c2 parser: Use peek_token instead of lookahead on the modifier path (#22842) (Boshen) - 9e496a7 semantic: Defer declare lookup for empty accessors (#22810) (camc314)
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What
In
parse_delimited_listandparse_delimited_list_into(cursor.rs), the loop already cacheslet kind = self.cur_kind();at the top of each iteration, then re-reads the same token viaif !self.at(separator)— which expands toself.token.kind() == separator.No token mutation (
advance/bump/next_token) happens between the cache and the separator check, so!self.at(separator)is provably identical tokind != separator. This reuses the already-loadedkindand avoids re-readingself.tokenonce per element of every array literal, object literal, parameter list, and argument list.Correctness
Semantics-preserving — no change to parse results or diagnostics.
cargo test -p oxc_parser: passcargo coverage -- parser: zero conformance snapshot diff (Test262 / TypeScript / Babel / estree)just fmt+cargo clippy -p oxc_parser --all-features --all-targets: cleanPerformance
A micro-optimization (removes one in-register/L1 token-field comparison per delimited-list element). Measured via an interleaved A/B against a parse-invariant control (
estree/checker.ts); combined with the modifier-path change it lands ~0.5–1% on declaration/member-dense files (binder.ts), noise-level elsewhere. The main value is making the reuse of the cachedkindexplicit.🤖 Generated with Claude Code