refactor(parser): remove lexer lookahead in JS statement parsing

[camchenry]

• part of parser: use checkpoints instead of token lookahead #11194

Removes more usage of lexer lookahead methods in favor of using the parser lookahead. This is all pretty much 1:1 conversions based on the existing code and the TS parser.

[camchenry]

• refactor(parser): remove lexer lookahead in object parsing #11274
• refactor(parser): remove lexer lookahead in JS statement parsing #11273 👈 (View in Graphite)
• main

---

How to use the Graphite Merge Queue

Add either label to this PR to merge it via the merge queue:

• 0-merge - adds this PR to the back of the merge queue
• hotfix - for urgent hot fixes, skip the queue and merge this PR next

You must have a Graphite account in order to use the merge queue. Sign up using this link.

An organization admin has enabled the Graphite Merge Queue in this repository.

Please do not merge from GitHub as this will restart CI on PRs being processed by the merge queue.

This stack of pull requests is managed by Graphite. Learn more about stacking.

[Copilot]

Pull Request Overview

This PR refactors JS statement parsing by replacing direct lexer lookahead calls with parser lookahead closures and adds helper methods for common lookahead patterns.

• Replaced peek_token, peek_kind, and nth usage with self.lookahead closures.
• Introduced is_using_declaration, is_next_token_binding_identifier_or_start_of_object_destructuring_on_same_line, is_using_statement, and is_next_token_using_keyword_then_binding_identifier helpers.
• Consolidated several multi-token peek checks into parser-based lookahead.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
crates/oxc_parser/src/js/statement.rs	Converted lexer lookahead to parser lookahead and added helpers
crates/oxc_parser/src/js/declaration.rs	Added helper is_using_statement and its lookahead predicate

Comments suppressed due to low confidence (2)

crates/oxc_parser/src/js/statement.rs:433

• [nitpick] The helper method name is very long and reduces readability; consider renaming to something more concise or splitting into focused helpers.

fn is_next_token_binding_identifier_or_start_of_object_destructuring_on_same_line(

crates/oxc_parser/src/js/statement.rs:427

• The new helper is_using_declaration isn’t covered by unit tests; consider adding tests for edge cases like line breaks and different token sequences.

fn is_using_declaration(&mut self) -> bool {

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #11273 will degrade performances by 11.43%

_{Comparing 05-24-refactor_parser_remove_lexer_lookahead_in_js_statement_parsing (8a062b5) with main (d6fc750)}

Summary

❌ 1 regressions
✅ 37 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	mangler[cal.com.tsx]	2.7 ms	3 ms	-11.43%

[graphite-app]

Merge activity

• May 25, 3:38 AM UTC: Boshen added this pull request to the Graphite merge queue.
• May 25, 3:45 AM UTC: Merged by the Graphite merge queue.