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perf(formatter): accumulate JSX child-list builders on the heap#24585

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07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap
Jul 22, 2026
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perf(formatter): accumulate JSX child-list builders on the heap#24585
graphite-app[bot] merged 1 commit into
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07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap

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@leaysgur leaysgur commented Jul 16, 2026 •
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The JSX child-list builders (MultilineBuilder / FlatBuilder in child_list.rs) were the last IR staging path still growing vectors in the arena.

They accumulate elements across the whole child-list loop while arbitrary child content is
formatted in between, so every growth stranded its old allocation (the same pattern #24582 removed from intern / BestFitting / grouped arguments).

They can't use HeapVecBuffer: the flat and multiline builders write alternately for each child, which would interleave their segments in the shared scratch vector and break its LIFO watermark discipline. The thread-local cache behind it has no such requirement though.

So each builder now checks out its own ScratchBuffer and writes into it through a small private Buffer adapter (ChildListBuffer); the finished result reaches the arena as one exactly-sized copy via the new Formatter::intern_elements, which clears the source so its capacity returns to the cache on drop.

Now arena reallocs for RadixUIAdoptionSection.jsx is 0.

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leaysgur requested a review from overlookmotel as a code owner July 16, 2026 06:39
@github-actions github-actions Bot added the A-formatter Area - Formatter label Jul 16, 2026
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leaysgur commented Jul 16, 2026 •
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@leaysgur leaysgur mentioned this pull request Jul 16, 2026
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Merging this PR will not alter performance

✅ 57 untouched benchmarks
⏩ 19 skipped benchmarks1

Comparing 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap (679a9e8) with 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers (c3b460b)

Open in CodSpeed

Footnotes

  1. 19 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. ↩

@leaysgur
leaysgur force-pushed the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch from 0c8e314 to 4a5c078 Compare July 16, 2026 06:53
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oxc-guard Bot commented Jul 16, 2026 •
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Oxfmt Ecosystem CI

suite oxfmt@latest main refs/pull/24585/head branch
monkeytypegame/monkeytype ❌ ✅ ✅
AmanVarshney01/create-better-t-stack ✅ ✅ ✅
actualbudget/actual ❌ ✅ ✅
fuma-nama/fumadocs ✅ ✅ ✅
cnpm/cnpmcore ❌ ✅ ✅
formatjs/formatjs ❌ ✅ ✅
tale/headplane ❌ ✅ ✅
eggjs/egg ❌ ✅ ✅
Comfy-Org/ComfyUI_frontend ⚠️ ✅ ✅
fastify/fastify-vite ❌ ✅ ✅
huggingface/huggingface.js ❌ ✅ ✅
dyad-sh/dyad ❌ ✅ ✅
lichess-org/lila ❌ ✅ ✅
vercel/turborepo ✅ ✅ ✅
vuejs/pinia ❌ ✅ ✅
openclaw/openclaw ❌ ✅ ✅
cloudflare/agents ❌ ✅ ✅
getsentry/sentry-javascript ❌ ✅ ✅
npmx-dev/npmx.dev ❌ ✅ ✅
mantinedev/mantine ❌ ✅ ✅
cloudflare/workers-sdk ❌ ✅ ✅
mastodon/mastodon ✅ ✅ ✅
vuejs/core ❌ ✅ ✅
aidenybai/react-grab ✅ ✅ ✅
rolldown/rolldown ❌ ✅ ✅

💥 = panic, ⚠️ = error e.g. parse error (main/branch columns: only new errors), ❌ = diff or exit code mismatch, 🟨 = differs from oxfmt@latest (merged-but-unreleased changes)

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leaysgur force-pushed the 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers branch from 72ae10f to c835270 Compare July 17, 2026 06:03
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leaysgur force-pushed the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch from 4a5c078 to d9a6184 Compare July 17, 2026 06:03
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leaysgur force-pushed the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch from d9a6184 to 8510ba2 Compare July 21, 2026 06:11
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leaysgur force-pushed the 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers branch from c835270 to 7aa30a3 Compare July 21, 2026 06:11
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leaysgur force-pushed the 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers branch from 7aa30a3 to a9a2c78 Compare July 21, 2026 09:26
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leaysgur force-pushed the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch from 8510ba2 to 0433b79 Compare July 21, 2026 09:26
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leaysgur force-pushed the 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers branch from a9a2c78 to c3b460b Compare July 22, 2026 05:04
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leaysgur force-pushed the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch from 0433b79 to 679a9e8 Compare July 22, 2026 05:04
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@leaysgur
perf(formatter): accumulate JSX child-list builders on the heap (#24585)
94de05f 
The JSX child-list builders (`MultilineBuilder` / `FlatBuilder` in `child_list.rs`) were the last IR staging path still growing vectors in the arena.

They accumulate elements across the whole child-list loop while arbitrary child content is
formatted in between, so every growth stranded its old allocation (the same pattern #24582 removed from `intern` / `BestFitting` / grouped arguments).

They can't use `HeapVecBuffer`: the flat and multiline builders write *alternately* for each child, which would interleave their segments in the shared scratch vector and break its LIFO watermark discipline. The thread-local cache behind it has no such requirement though.

So each builder now checks out its own `ScratchBuffer` and writes into it through a small private `Buffer` adapter (`ChildListBuffer`); the finished result reaches the arena as one exactly-sized copy via the new `Formatter::intern_elements`, which clears the source so its capacity returns to the cache on drop.

Now arena reallocs for `RadixUIAdoptionSection.jsx` is 0.
@graphite-app
graphite-app Bot force-pushed the 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers branch from c3b460b to 7810e8a Compare July 22, 2026 06:32
@graphite-app
graphite-app Bot force-pushed the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch from 679a9e8 to 94de05f Compare July 22, 2026 06:33
@graphite-app graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Jul 22, 2026
Base automatically changed from 07-16-perf_formatter_core_share_one_thread-cached_scratch_vector_across_staging_buffers to main July 22, 2026 06:37
@graphite-app
graphite-app Bot merged commit 94de05f into main Jul 22, 2026
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@graphite-app
graphite-app Bot deleted the 07-16-perf_formatter_accumulate_jsx_child-list_builders_on_the_heap branch July 22, 2026 06:39
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