refactor(parser): align jsx parsing to tsc

[leaysgur]

My original plan was to rework the JSX parser from the entry point, as I had found in #11232.

However, when I read through all the TSC JSX parser code, I found that what we are doing is not much different.

---

As for perf perspective, the OXC currently requires rewind in 3 places for JSX:

• 1: parse_jsx_expression() - lookahead
  • To determine if it is a JSXElement(<C) OR JSXFragment(<>) at the entry point
• 2: parse_jsx_child() - checkpoint+rewind
  • The same above OR breaking list(</)
• 3: parse_jsx_child() - checkpoint+rewind
  • To determine if it is JSXChild::Spread({...Expression}) OR JSXChild::ExpressionContainer({JSXExpression})

These don't exist in TSC, they just use union type or loose ASTs.

But we have different and explicit ASTs in Rust, it seems they can't be easily eliminated.

And unfortunately, I tried, but there was no remarkable improvement.

• For 1, 3045952 => Minifier +3%, but no effect for parser
• For 2, I wish we had Kind::LessThanSlash...
• For 3, a12ff21 => No effect for parser

As a result, I think it would be better to keep the current clean and explicit code.

[graphite-app]

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #11314 will degrade performances by 8.23%

_{Comparing r/jsx (08eb1eb) with main (b53b053)}

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]	2.8 ms	3 ms	-8.23%

[Copilot]

Pull Request Overview

This PR refactors the JSX parser to mirror TypeScript’s approach by centralizing JSX element and fragment parsing and updating lookahead logic.

• Replaced manual lookahead branches in parse_jsx_attribute_value with a unified parse_jsx_expression match.
• Enhanced parse_literal_or_identifier lookahead to detect fragments via Kind::RAngle.
• Removed outdated JSX comment and streamlined fragment detection.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
crates/oxc_parser/src/jsx/mod.rs	Simplify attribute value parsing using parse_jsx_expression
crates/oxc_parser/src/js/expression.rs	Extend lookahead to recognize <> fragment start

Comments suppressed due to low confidence (1)

crates/oxc_parser/src/js/expression.rs:1018

• The new lookahead condition for fragment detection (p.at(Kind::RAngle)) isn't covered by existing tests. Add a parser test case for <> ... </> inside expressions to ensure this branch is exercised.

p.at(Kind::RAngle) || p.cur_kind().is_identifier_or_keyword()

[Boshen]

Merge activity

• May 27, 8:58 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 27, 8:58 AM UTC: Boshen added this pull request to the Graphite merge queue.
• May 27, 9:05 AM UTC: Merged by the Graphite merge queue.