fix(codegen): preserve comments before expression operands by Dunqing · Pull Request #24510 · oxc-project/oxc

Dunqing · 2026-07-14T14:31:17Z

Coverage directives attached to expression operands were silently dropped by codegen in logical right-hand sides, conditional consequents, object property values, and template literal interpolations. The AST expressions survive, but those emitters never consume their leading comment groups.

Print the comment group at each surviving expression boundary, probing parenthesized layers (a || /* c */ (x) anchors the comment at the (, a || (/* c */ x) at x). Parenthesized function and arrow IIFEs keep comments inside their generated wrapper.

Logical right-hand sides and conditional consequents only print groups containing annotations. This is codegen policy for mutated ASTs: comments are anchored by source position, and mutating consumers (minifier statement merging, rolldown finalization) move statements into exactly these positions — a dissolved statement's leading normal-comment group can coincide with the moved operand's span start, and printing it there misplaces statement-level trivia and breaks minify-twice idempotency (test262 language/asi/S7.9_A5.8_T1.js and friends). Annotations are the one comment kind with expression-level meaning, so they pass through.

Printing comments at expression boundaries also exposed three latent spacing bugs in the shared comment printer, surfaced by monitor-oxc over real node_modules: a full indent was injected before mid-line groups (doubling indentation on every pass, invisible at indent 0), a group ending in a newline left the next operand at column 0, and minify-with-comments mode emitted a glue space or not depending on which printer consumed the group. All three are fixed with regression tests.

Example

Input:

const value = a ?? /* istanbul ignore next */ [];

Before:

const value = a ?? [];

After:

const value = a ?? /* istanbul ignore next */ [];

Verified with cargo test -p oxc_codegen (134 tests), full cargo coverage (minifier at baseline, zero snapshot drift), --twice idempotency over webpack/typescript/eslint-utils/storybook/sigstore files in plain, dce, and minify-with-comments modes, and monitor-oxc green on codegen/dce/whitespace/transformer (remaining failures are main's pre-existing baseline).

closes #21301
closes #22049
closes #24324

This PR was assisted by OpenAI Codex and Claude.

Dunqing · 2026-07-14T14:31:31Z

fix(codegen): preserve comments before expression operands #24510 👈 (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 changes, fast-track this PR to the front of the merge queue

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 · 2026-07-14T14:38:47Z

Merging this PR will not alter performance

✅ 57 untouched benchmarks
⏩ 14 skipped benchmarks¹

_{Comparing fix/codegen-preserve-expression-comments (5026d0d) with main (91541dd)²}

14 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 main (4279eca) during the generation of this report, so 91541dd was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

oxc-guard · 2026-07-14T14:58:51Z

Monitor Oxc

Commit: 08cac9e37476

suite	result
Test262	❌
Build	✅
Uglify Corpus	✅
Isolated Declarations	✅
Runtime Bundles	✅
(transformer)	✅
(mangler)	❌
(compressor)	✅
(whitespace)	✅
(codegen)	✅
(dce)	✅
(formatter)	❌
(formatter_dcr)	✅
Runtime (solid)	✅
Runtime (zod)	✅
Runtime (svelte)	✅
Runtime (es-toolkit)	✅
Runtime (vue)	✅

Boshen

Can you do a few more round of reviews to make the code minimal and clean?

Dunqing · 2026-07-15T09:09:19Z

Can you do a few more round of reviews to make the code minimal and clean?

Let me try

Dunqing · 2026-07-15T15:59:58Z

I am going to merge this as the first step, as there is no more room to simplify if we don't make some changes in the existing comments handling beforehand. I am chatting with Codex to explore a more generic approach to printing comments as a follow-up.

Dunqing · 2026-07-15T16:00:09Z

Merge activity

Jul 15, 4:00 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Jul 15, 4:00 PM UTC: Dunqing added this pull request to the Graphite merge queue.
Jul 15, 4:06 PM UTC: Merged by the Graphite merge queue.

Coverage directives attached to expression operands were silently dropped by codegen in logical right-hand sides, conditional consequents, object property values, and template literal interpolations. The AST expressions survive, but those emitters never consume their leading comment groups. Print the comment group at each surviving expression boundary, probing parenthesized layers (`a || /* c */ (x)` anchors the comment at the `(`, `a || (/* c */ x)` at `x`). Parenthesized function and arrow IIFEs keep comments inside their generated wrapper. Logical right-hand sides and conditional consequents only print groups containing annotations. This is codegen policy for mutated ASTs: comments are anchored by source position, and mutating consumers (minifier statement merging, rolldown finalization) move statements into exactly these positions — a dissolved statement's leading normal-comment group can coincide with the moved operand's span start, and printing it there misplaces statement-level trivia and breaks minify-twice idempotency (test262 `language/asi/S7.9_A5.8_T1.js` and friends). Annotations are the one comment kind with expression-level meaning, so they pass through. Printing comments at expression boundaries also exposed three latent spacing bugs in the shared comment printer, surfaced by monitor-oxc over real node_modules: a full indent was injected before mid-line groups (doubling indentation on every pass, invisible at indent 0), a group ending in a newline left the next operand at column 0, and minify-with-comments mode emitted a glue space or not depending on which printer consumed the group. All three are fixed with regression tests. ## Example Input: ```js const value = a ?? /* istanbul ignore next */ []; ``` Before: ```js const value = a ?? []; ``` After: ```js const value = a ?? /* istanbul ignore next */ []; ``` Verified with `cargo test -p oxc_codegen` (134 tests), full `cargo coverage` (minifier at baseline, zero snapshot drift), `--twice` idempotency over webpack/typescript/eslint-utils/storybook/sigstore files in plain, dce, and minify-with-comments modes, and monitor-oxc green on codegen/dce/whitespace/transformer (remaining failures are main's pre-existing baseline). closes #21301 closes #22049 closes #24324 This PR was assisted by OpenAI Codex and Claude.

### 💥 BREAKING CHANGES - 54cc121 ast: [**BREAKING**] Split `MetaProperty` into `ImportMeta` and `NewTarget` (#24557) (camc314) ### 🚀 Features - 4c71560 parser: More friendly error for spread element in dynamic imports (#24705) (sapphi-red) - 7b045cd minfier: Drop last break from last switch case (#24673) (Armano) - 7d3c178 minifier: Remove unreachable recursive functions (#24125) (Dunqing) - 94f99b3 ast: Allow `NONE` to be passed to AST builder methods where `Option<ArenaVec>` is expected (#24629) (overlookmotel) - 77230c5 ast: Accept arrays for `ArenaVec` params of AST builder methods (#24621) (overlookmotel) - f08b152 allocator: Implement `FromIn` for array to `Vec` conversion (#24620) (overlookmotel) - 2338c13 track-memory-allocations: Track heap deallocs, alloc bytes, and peak growth (#24619) (Boshen) - 7aa4739 syntax,transformer: Move JSX entity decoder to `oxc_syntax` (#24617) (camc314) - 2b097c4 str: Export `Str` as `ArenaStr` (#24604) (overlookmotel) - 3acf4c1 minifier: Expand switch optimiation to remove empty cases (#24520) (Armano) - 129b759 parser: Improve diagnostics for unparenthesized LHS on exponential expr (#24569) (camc314) - 4d0c601 minifier: Fold arithmetic over undefined and null operands (#24485) (Dunqing) - 91541dd minifier: Drop empty switch statements (#24527) (Armano) - d05224d ast_visit: Generate VisitJs visitor that skips TypeScript type-space (#24499) (Boshen) - 3d22307 parser: Add `ParseOptions::enable_ident_hashes` (#24491) (Boshen) ### 🐛 Bug Fixes - 64c2241 minifier: Align class heritage removal with assumptions (#24533) (Dunqing) - 48b59f4 parser: Span ambient generator diagnostics (#24711) (camc314) - e750a82 ecmascript: Fix false negative for may_have_side_effects on dynamic property access (#24709) (sapphi-red) - f145d73 minifier: Guard reordered identifier reads (#24698) (Dunqing) - a2ef382 isolated-declarations: Reject `window.Symbol` as global symbol reference (#24689) (camc314) - b1bcf72 minifier: Invalidate facts for redeclared bindings (#24658) (Dunqing) - 921b834 minifier: Don't treat a conditionally-assigned var as write-once (#24650) (Dunqing) - 061af1f minifier: Avoid stale pure function summaries (#24636) (Dunqing) - 40c2f43 allocator: `Vec::from_array_in` do not allocate zero-length array (#24628) (overlookmotel) - 70994ae codegen: Preserve comments before expression operands (#24510) (Dunqing) - 7b4baff parser: Reject new import member access (#23459) (camc314) - 128b385 minifier: Clippy warning with no-debug-assertions (#24547) (camc314) - 8421feb parser: Use first `as` span for imported name (#24537) (leaysgur) - c517aa0 parser: Reject invalid accessor assertions (#24504) (camc314) ### ⚡ Performance - 884d9eb parser: Pre-size cover-grammar assignment target buffers (#24683) (Boshen) - d3f07a0 diagnostics: Box OxcDiagnosticInner to reduce binary size (#24665) (Boshen) - bcc9de0 parser: Defer diagnostic creation until parse exit (#24663) (Boshen) - c35d8ab allocator: Mark `ReplaceWith` panic path cold (#24515) (camc314) - ba65790 semantic, allocator: Branchless `clone_in` for semantic IDs (#24564) (overlookmotel) - 747feec parser: Build AST nodes with the AST builder instead of cloning (#24540) (Boshen) - ba35a0d react_compiler: Use IndexVec for dense id-keyed maps (#24549) (Boshen) - b685062 react_compiler: Keep small hot-path collections inline (#24514) (Marius Schulz) - a149e95 transformer: Outline rare expression exits (#24512) (camc314) - 7808a6e react_compiler: Make aliasing effects cheap to intern and clone (#24506) (Marius Schulz) - 3a36f2a react_compiler: Store AbstractValue reasons as a u16 bitmask (#24480) (Boshen) - 1c96753 react_compiler: Use FxHashMap for the lookup-only aliasing node map (#24490) (Boshen) Co-authored-by: Cameron <[email protected]>

github-actions Bot added the A-codegen Area - Code Generation label Jul 14, 2026

Dunqing added the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 14, 2026

oxc-guard Bot removed the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 14, 2026

Dunqing added the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 14, 2026

oxc-guard Bot removed the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 14, 2026

Dunqing added the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 15, 2026

oxc-guard Bot removed the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 15, 2026

Dunqing added the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 15, 2026

oxc-guard Bot removed the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 15, 2026

Dunqing marked this pull request as ready for review July 15, 2026 06:17

Dunqing requested review from Boshen and camc314 July 15, 2026 08:20

Boshen approved these changes Jul 15, 2026

View reviewed changes

Dunqing added the 0-merge Merge with Graphite Merge Queue label Jul 15, 2026

graphite-app Bot force-pushed the fix/codegen-preserve-expression-comments branch from 5026d0d to 70994ae Compare July 15, 2026 16:01

graphite-app Bot merged commit 70994ae into main Jul 15, 2026
29 checks passed

graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Jul 15, 2026

graphite-app Bot deleted the fix/codegen-preserve-expression-comments branch July 15, 2026 16:06

Dunqing mentioned this pull request Jul 15, 2026

fix(codegen): preserve normal comments before operands #24567

Draft

camc314 mentioned this pull request Jul 15, 2026

fix(codegen): preserve comments before ConditionalExpression consequent #21325

Closed

oxc-guard Bot mentioned this pull request Jul 20, 2026

release(crates): oxc v0.141.0 #24714

Merged

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

fix(codegen): preserve comments before expression operands#24510

fix(codegen): preserve comments before expression operands#24510
graphite-app[bot] merged 1 commit into
mainfrom
fix/codegen-preserve-expression-comments

Dunqing commented Jul 14, 2026 •

edited

Loading

Uh oh!

Dunqing commented Jul 14, 2026

Uh oh!

codspeed-hq Bot commented Jul 14, 2026 •

edited

Loading

Uh oh!

oxc-guard Bot commented Jul 14, 2026 •

edited

Loading

Uh oh!

Boshen left a comment

Uh oh!

Dunqing commented Jul 15, 2026

Uh oh!

Dunqing commented Jul 15, 2026

Uh oh!

Dunqing commented Jul 15, 2026 •

edited by graphite-app Bot

Loading

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Uh oh!

Conversation

Dunqing commented Jul 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Example

Uh oh!

Dunqing commented Jul 14, 2026

How to use the Graphite Merge Queue

Uh oh!

codspeed-hq Bot commented Jul 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Merging this PR will not alter performance

Footnotes

Uh oh!

oxc-guard Bot commented Jul 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Monitor Oxc

Uh oh!

Boshen left a comment

Choose a reason for hiding this comment

Uh oh!

Dunqing commented Jul 15, 2026

Uh oh!

Dunqing commented Jul 15, 2026

Uh oh!

Dunqing commented Jul 15, 2026 • edited by graphite-app Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Merge activity

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Dunqing commented Jul 14, 2026 •

edited

Loading

codspeed-hq Bot commented Jul 14, 2026 •

edited

Loading

oxc-guard Bot commented Jul 14, 2026 •

edited

Loading

Dunqing commented Jul 15, 2026 •

edited by graphite-app Bot

Loading