refactor(parser): remove lexer lookahead in parsing TS statements

[camchenry]

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

removes usage of nth, peek, etc. to stop using the lexer lookahead functionality, so that we can remove it.

• Removed is_at_interface_declaration: this wasn't necessary to check as far as I can tell, the TS parser doesn't do this and just removing it doesn't impact conformance currently
• Simplified is_at_ts_index_signature_member: this had a lot of usage of nth so I made it a simpler function that works with lookahead instead
• Moved/refactored is_nth_at_modifier: once I changed the is_at_ts_index_signature_member check, we no longer used this in the statements.rs file, so I moved it close to the only place it was still used. then, I refactored it to remove any peek/nth usage, as well as refactoring to do an early return as soon as possible.

[camchenry]

• refactor(parser): remove lexer lookahead in parsing TS statements #11253 👈 (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.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #11253 will not alter performance

_{Comparing 05-23-refactor_linter_remove_lexer_lookahead_in_parsing_ts_statements (b99749c) with main (dcdcf12)}

Summary

✅ 38 untouched benchmarks

[Copilot]

Pull Request Overview

This PR refactors TypeScript statement parsing by removing direct lexer lookahead (nth, peek) and replacing it with controlled lookahead usage and checkpoint-based checks.

• Introduces is_at_modifier to replace is_nth_at_modifier
• Simplifies TS index signature and interface declaration detection using lookahead-based helpers
• Updates parsing of type aliases, import-equals, and export statements to use new lookahead methods

Reviewed Changes

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

File	Description
crates/oxc_parser/src/ts/types.rs	Added is_at_modifier and updated modifier parsing in TS types
crates/oxc_parser/src/ts/statement.rs	Replaced peek/nth calls with lookahead, refactored several TS statement parsers, removed is_at_interface_declaration

Comments suppressed due to low confidence (2)

crates/oxc_parser/src/ts/statement.rs:127

• [nitpick] The variable name ty is quite short and might be unclear; consider renaming it to annotation or typeAnnotation for clarity and consistency.

let ty = if self.at(Kind::Intrinsic) && !self.lookahead(Self::is_next_token_dot) {

crates/oxc_parser/src/ts/statement.rs:147

• [nitpick] The lookahead helper naming is inconsistent (is_next_token_dot, is_next_token_equals, is_next_token_open_paren_or_angle_bracket); consider a uniform naming convention like lookahead_is_* to improve readability.

fn is_next_token_dot(&mut self) -> bool {

[Boshen]

Merge activity

• May 24, 2:24 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• May 24, 2:24 AM UTC: Boshen added this pull request to the Graphite merge queue.
• May 24, 2:30 AM UTC: Merged by the Graphite merge queue.