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Skip loadBindings() Lightning CSS check during next start - #91538

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sokra merged 1 commit into
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sokra/no-lightningcss-in-next-start
Mar 19, 2026
Merged

Skip loadBindings() Lightning CSS check during next start#91538
sokra merged 1 commit into
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sokra/no-lightningcss-in-next-start

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@sokra sokra commented Mar 17, 2026 •
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Summary

Avoid calling loadBindings() to check whether the loaded binary supports Lightning CSS during next start, as this is unnecessary for production server operation. The check should only occur during the build phase.

  • Skips the native binary load during next start (production server phase)
  • No impact on build, development, or export phases
  • Reduces production server startup overhead

Test plan

  • Build and start tests passing
  • CI green (except pre-existing flaky cache components test in rerun)

@sokra
sokra requested a review from mischnic March 17, 2026 21:47
@sokra
sokra marked this pull request as ready for review March 17, 2026 21:47
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Notifying the following users due to files changed in this PR based on this repo's notify modifiers:

@timneutkens, @ijjk, @shuding, @huozhi:

packages/next/src/server/config.ts

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nextjs-bot commented Mar 17, 2026 •
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Tests Passed

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nextjs-bot commented Mar 17, 2026 •
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Stats from current PR

✅ No significant changes detected

📊 All Metrics
📖 Metrics Glossary

Dev Server Metrics:

  • Listen = TCP port starts accepting connections
  • First Request = HTTP server returns successful response
  • Cold = Fresh build (no cache)
  • Warm = With cached build artifacts

Build Metrics:

  • Fresh = Clean build (no .next directory)
  • Cached = With existing .next directory

Change Thresholds:

  • Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
  • Size: Changes < 1KB AND < 1% are insignificant
  • All other changes are flagged to catch regressions

⚡ Dev Server

Metric Canary PR Change Trend
Cold (Listen) 457ms 455ms ✓ ▁▁█▁▁
Cold (Ready in log) 441ms 445ms ✓ ▁▁▇▁▁
Cold (First Request) 1.081s 1.113s ✓ ▂▁█▂▁
Warm (Listen) 457ms 456ms ✓ ▁▁█▁▁
Warm (Ready in log) 446ms 446ms ✓ ▁▁█▁▁
Warm (First Request) 343ms 347ms ✓ ▁▁█▁▁
📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric Canary PR Change Trend
Cold (Listen) 457ms 456ms ✓ █▁▁▁█
Cold (Ready in log) 446ms 443ms ✓ ▁▁▁▁▁
Cold (First Request) 1.973s 1.981s ✓ ████▃
Warm (Listen) 456ms 456ms ✓ ▅▅▅▅▁
Warm (Ready in log) 442ms 445ms ✓ ▁▁▁▁▁
Warm (First Request) 1.943s 1.960s ✓ ▇██▇▃

⚡ Production Builds

Metric Canary PR Change Trend
Fresh Build 3.780s 3.820s ✓ ▁▁█▁▁
Cached Build 3.761s 3.810s ✓ ▁▁█▁▁
📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric Canary PR Change Trend
Fresh Build 14.480s 14.562s ✓ ▄▄▄▄▃
Cached Build 14.592s 14.689s ✓ ▅▅▄▄▄
node_modules Size 484 MB 484 MB ✓ █████
📦 Bundle Sizes

Bundle Sizes

⚡ Turbopack

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Server

Middleware
Canary PR Change
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Total 711 B 714 B ⚠️ +3 B
Build Details
Build Manifests
Canary PR Change
_buildManifest.js gzip 433 B 426 B 🟢 7 B (-2%)
Total 433 B 426 B ✅ -7 B

📦 Webpack

Client

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Canary PR Change
5528-HASH.js gzip 5.54 kB N/A -
6280-HASH.js gzip 60.4 kB N/A -
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Polyfills
Canary PR Change
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Total 39.4 kB 39.4 kB ✓
Pages
Canary PR Change
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Total 7.98 kB 7.98 kB ✅ -1 B

Server

Edge SSR
Canary PR Change
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Total 394 kB 394 kB ✅ -310 B
Middleware
Canary PR Change
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Total 45.7 kB 45.4 kB ✅ -232 B
Build Details
Build Manifests
Canary PR Change
_buildManifest.js gzip 715 B 718 B ✓
Total 715 B 718 B ⚠️ +3 B
Build Cache
Canary PR Change
0.pack gzip 4.28 MB 4.27 MB 🟢 5.08 kB (0%)
index.pack gzip 109 kB 110 kB 🔴 +1.27 kB (+1%)
index.pack.old gzip 111 kB 110 kB 🟢 1.21 kB (-1%)
Total 4.5 MB 4.49 MB ✅ -5.02 kB

🔄 Shared (bundler-independent)

Runtimes
Canary PR Change
app-page-exp...dev.js gzip 333 kB 333 kB ✓
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app-page-tur..prod.js gzip 181 kB 181 kB ✓
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app-route.ru...dev.js gzip 75.7 kB 75.7 kB ✓
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📎 Tarball URL 
https://vercel-packages.vercel.app/next/commits/42ea8bfe7f3d840708b14540655e0f855b691184/next

@sokra @claude
Skip loadBindings() Lightning CSS check during next start
42ea8bf 
The capability check is only needed at build time. During PHASE_PRODUCTION_SERVER
the app is already built and no CSS compilation occurs, so loading the native SWC
binary to check css.lightning support is wasted work.

Co-Authored-By: Claude <noreply@anthropic.com>
@sokra
sokra force-pushed the sokra/no-lightningcss-in-next-start branch from be37fe8 to 42ea8bf Compare March 19, 2026 07:37
@sokra
sokra enabled auto-merge (squash) March 19, 2026 08:45
@sokra
sokra merged commit 6f669f1 into canary Mar 19, 2026
409 of 416 checks passed
@sokra
sokra deleted the sokra/no-lightningcss-in-next-start branch March 19, 2026 09:00
@github-actions github-actions Bot added the locked label Apr 2, 2026
@github-actions github-actions Bot locked as resolved and limited conversation to collaborators Apr 2, 2026
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@lukesandberg lukesandberg lukesandberg approved these changes
@mischnic mischnic mischnic approved these changes

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created-by: Turbopack team PRs by the Turbopack team. locked type: next

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@sokra @nextjs-bot @lukesandberg @mischnic