perf(transformer): only scan comments before first statement for JSX pragmas by Dunqing · Pull Request #20675 · oxc-project/oxc

Dunqing · 2026-03-24T02:10:02Z

Summary

Restrict JSX pragma scanning to only comments appearing before the first statement, since pragmas are file-level directives
Pass first_statement_start position to update_options_with_comments and skip comments at or after that position

Motivation

Previously all comments in a file were scanned for JSX pragmas, which meant pragmas in doc comments on functions could override file-level pragmas. This aligns Oxc with TypeScript and SWC, which both restrict pragma scanning to leading comments.

Tool	Pragma scan scope
TypeScript	Leading comments before first token
SWC	Leading block comments, stops at first pragma-bearing statement
Babel	All comments (last wins)
esbuild	All comments (last wins)
Oxc (after)	Comments before first statement

Test plan

All transformer tests pass
Conformance tests pass (including issue-20669 fixture from parent PR)
Clippy clean

🤖 Generated with Claude Code

Dunqing · 2026-03-24T02:10:15Z

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codspeed-hq · 2026-03-24T02:15:44Z

Merging this PR will not alter performance

✅ 49 untouched benchmarks
⏩ 7 skipped benchmarks¹

_{Comparing refactor/jsx-pragma-leading-comments-only (cd25e3f) with fix/jsx-pragma-backtick (da1550c)²}

7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
No successful run was found on fix/jsx-pragma-backtick (9439b5d) during the generation of this report, so e8697ce was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

Dunqing · 2026-03-24T03:27:56Z

@sapphi-red I'd like to hear your thoughts on this, as this would diverge from esbuild and babel but align with typescript and swc. I think it is fine. What do you think?

sapphi-red

I think this behavior makes sense and I wouldn't expect any code to break by this change.

Maybe we should clarify the behavior in https://oxc.rs/docs/guide/usage/transformer/jsx.html, adding a section about how pragma comments are parsed

Dunqing · 2026-03-24T09:21:12Z

Maybe we should clarify the behavior in https://oxc.rs/docs/guide/usage/transformer/jsx.html, adding a section about how pragma comments are parsed

Thank you for reminding me. I will send a PR to follow it later

Dunqing · 2026-03-24T09:22:21Z

Merge activity

Mar 24, 9:22 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Mar 24, 9:22 AM UTC: Dunqing added this pull request to the Graphite merge queue.
Mar 24, 9:27 AM UTC: Merged by the Graphite merge queue.

…pragmas (#20675) ## Summary - Restrict JSX pragma scanning to only comments appearing before the first statement, since pragmas are file-level directives - Pass `first_statement_start` position to `update_options_with_comments` and skip comments at or after that position ## Motivation Previously all comments in a file were scanned for JSX pragmas, which meant pragmas in doc comments on functions could override file-level pragmas. This aligns Oxc with TypeScript and SWC, which both restrict pragma scanning to leading comments. | Tool | Pragma scan scope | |------|-------------------| | TypeScript | Leading comments before first token | | SWC | Leading block comments, stops at first pragma-bearing statement | | Babel | All comments (last wins) | | esbuild | All comments (last wins) | | **Oxc (after)** | Comments before first statement | ## Test plan - [x] All transformer tests pass - [x] Conformance tests pass (including `issue-20669` fixture from parent PR) - [x] Clippy clean 🤖 Generated with [Claude Code](https://claude.com/claude-code)

Clarify that Oxc only scans comments before the first statement for JSX pragmas, aligning with TypeScript and SWC behavior. This was requested in oxc-project/oxc#20675 review feedback. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Clarify that Oxc only scans comments before the first statement for JSX pragmas, aligning with TypeScript and SWC behavior. This was requested in oxc-project/oxc#20675 review feedback. Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Dunqing mentioned this pull request Mar 24, 2026

fix(transformer): ignore @jsxImportSource inside inline code spans in comments #20674

Merged

4 tasks

github-actions bot added A-transformer Area - Transformer / Transpiler C-cleanup Category - technical debt or refactoring. Solution not expected to change behavior labels Mar 24, 2026

Dunqing changed the title ~~refactor(transformer): only scan comments before first statement for JSX pragmas~~ perf(transformer): only scan comments before first statement for JSX pragmas Mar 24, 2026

github-actions bot added the C-performance Category - Solution not expected to change functional behavior, only performance label Mar 24, 2026

Dunqing force-pushed the refactor/jsx-pragma-leading-comments-only branch 2 times, most recently from a740466 to 225ded7 Compare March 24, 2026 02:20

Dunqing force-pushed the fix/jsx-pragma-backtick branch from 9ce3b27 to af50cc8 Compare March 24, 2026 02:36

Dunqing force-pushed the refactor/jsx-pragma-leading-comments-only branch 2 times, most recently from df98a5e to fa8b679 Compare March 24, 2026 02:38

Dunqing force-pushed the fix/jsx-pragma-backtick branch 2 times, most recently from da1550c to 9439b5d Compare March 24, 2026 03:25

Dunqing force-pushed the refactor/jsx-pragma-leading-comments-only branch from fa8b679 to cd25e3f Compare March 24, 2026 03:25

Dunqing marked this pull request as ready for review March 24, 2026 03:26

Dunqing requested a review from overlookmotel as a code owner March 24, 2026 03:26

Dunqing requested a review from sapphi-red March 24, 2026 03:26

sapphi-red approved these changes Mar 24, 2026

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Dunqing added the 0-merge Merge with Graphite Merge Queue label Mar 24, 2026

graphite-app bot force-pushed the fix/jsx-pragma-backtick branch from 9439b5d to 3931b98 Compare March 24, 2026 09:22

graphite-app bot force-pushed the refactor/jsx-pragma-leading-comments-only branch from cd25e3f to bd10021 Compare March 24, 2026 09:23

Base automatically changed from fix/jsx-pragma-backtick to main March 24, 2026 09:26

graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Mar 24, 2026

graphite-app bot merged commit bd10021 into main Mar 24, 2026
27 checks passed

graphite-app bot deleted the refactor/jsx-pragma-leading-comments-only branch March 24, 2026 09:27

Dunqing mentioned this pull request Mar 25, 2026

docs(transformer): document JSX pragma comment scanning behavior oxc-project/website#1016

Merged

Boshen mentioned this pull request Mar 30, 2026

release(crates): oxc v0.123.0 #20862

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perf(transformer): only scan comments before first statement for JSX pragmas#20675

perf(transformer): only scan comments before first statement for JSX pragmas#20675
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Summary

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Merging this PR will not alter performance

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