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[turbopack] Drop dead require() calls#95718

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[turbopack] Drop dead require() calls#95718
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@sampoder sampoder commented Jul 12, 2026 •
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This PR adds support for turbopackRemoveUnusedImports in CJS modules. If modules are side-effect free and their imports are unused we do the following re-writes:

require('./pure')          →   0;
console.log('x')               console.log('x')

const x = require('./pure')   →   const x = 0

const dead = require('./pure'), keep = 'v'   →   const dead = 0, keep = 'v'

const {} = require('./pure')   →   const {} = 0

if (cond) require('./pure')   →   if (cond) 0;

SWC should then drop the 0.

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Stats from current PR

🟢 1 improvement

Metric Canary PR Change Trend
Webpack Build Time 26.806s 26.215s 🟢 591ms (-2%) ▁▁▁▁█
📊 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) 762ms 763ms ✓ ▁▁▁▂█
Cold (Ready in log) 763ms 769ms ✓ ▁▁▁▁█
Cold (First Request) 1.289s 1.308s ✓ ▁▁▁▁█
Warm (Listen) 761ms 812ms ✓ ▁▁▁▁▇
Warm (Ready in log) 761ms 772ms ✓ ▁▁▁▁█
Warm (First Request) 1.284s 1.262s ✓ ▁▁▁▁█
📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric Canary PR Change Trend
Cold (Listen) 815ms 814ms ✓ ▂▁▂▁█
Cold (Ready in log) 812ms 800ms ✓ ▁▁▁▁█
Cold (First Request) 3.538s 3.468s ✓ ▁▁▂▁█
Warm (Listen) 813ms 813ms ✓ ▂▂▂▁█
Warm (Ready in log) 807ms 795ms ✓ ▁▁▁▁█
Warm (First Request) 3.496s 3.418s ✓ ▁▁▁▁█

⚡ Production Builds

Metric Canary PR Change Trend
Fresh Build 4.920s 4.885s ✓ ▁▁▁▁█
Cached Build 5.009s 5.023s ✓ ▁▁▁▁█
📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric Canary PR Change Trend
Fresh Build 26.806s 26.215s 🟢 591ms (-2%) ▁▁▁▁█
Cached Build 26.188s 26.536s ✓ ▁▁▁▁█
node_modules Size 516 MB 516 MB ✓ ▁▁▁▁█
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Total 409 kB 411 kB ⚠️ +2.17 kB
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🔄 Shared (bundler-independent)

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📎 Tarball URL 
https://vercel-packages.vercel.app/next/commits/63ffb6d034de8e7a6622e0a5563c11af0e949109/next

Commit: 63ffb6d

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Tests Passed

Commit: 63ffb6d

vercel[bot]
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Comment thread turbopack/crates/turbopack-ecmascript/src/references/cjs.rs
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/require-export-usage branch from f375c7a to 3466595 Compare July 12, 2026 18:06
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/drop-dead-requires branch from e4ab885 to d1b3118 Compare July 12, 2026 18:06
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/require-export-usage branch from 3466595 to e192eca Compare July 12, 2026 18:22
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/drop-dead-requires branch from d1b3118 to 39ac932 Compare July 12, 2026 18:22
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/require-export-usage branch from e192eca to a2c02ed Compare July 12, 2026 18:32
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/drop-dead-requires branch 3 times, most recently from d1eeb7c to a70e8e6 Compare July 12, 2026 19:33
@sampoder sampoder force-pushed the sp/turbopack/cjs-tree-shaking/drop-dead-requires branch from a70e8e6 to 63ffb6d Compare July 12, 2026 19:38
@sampoder sampoder requested a review from lukesandberg July 12, 2026 19:39
@sampoder sampoder marked this pull request as ready for review July 12, 2026 19:39
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