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nextjs - ✅(Solved) Fix Turbopack not tree-shaking unused enum exports [2 pull requests, 5 comments, 3 participants]

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vercel/next.js#88009•Fetched 2026-04-08 02:05:40
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Author
DRoetDRoet
Participants
christopherjohnson3028-stackchristopherjohnson3028-stackDRoetDRoetmischnicmischnic
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commented ×5subscribed ×5mentioned ×3cross-referenced ×2

Fix Action

Fixed

PR fix notes

PR #88205: Turbopack: properly remove unused TS enums with scope hoisting

Description (problem / solution / changelog)

Only adds a test so far

Closes https://github.com/vercel/next.js/issues/88009 Closes PACK-6424

Changed files

  • turbopack/crates/turbopack-tests/tests/execution/turbopack/scope-hoisting/pure-comments/input/a.ts (added, +3/-0)
  • turbopack/crates/turbopack-tests/tests/execution/turbopack/scope-hoisting/pure-comments/input/index.js (added, +13/-0)
  • turbopack/crates/turbopack-tests/tests/execution/turbopack/scope-hoisting/pure-comments/options.json (added, +3/-0)

PR #90004: Turbopack: properly remove unused TS enums with scope hoisting

Description (problem / solution / changelog)

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Attempt based on https://github.com/vercel/next.js/pull/88205. reserves SWC sentinel spans during scope-hoisting so PURE annotations survive module merging.

Closes https://github.com/vercel/next.js/issues/88009 Closes PACK-6424

@mischnic PTAL if this is the right approach

Changed files

  • turbopack/crates/turbopack-ecmascript/src/lib.rs (modified, +8/-0)
  • turbopack/crates/turbopack-tests/tests/execution/turbopack/scope-hoisting/pure-comments/input/a.ts (added, +3/-0)
  • turbopack/crates/turbopack-tests/tests/execution/turbopack/scope-hoisting/pure-comments/input/index.js (added, +17/-0)
  • turbopack/crates/turbopack-tests/tests/execution/turbopack/scope-hoisting/pure-comments/options.json (added, +3/-0)

Code Example

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 63146
  Available CPU cores: 16
Binaries:
  Node: 24.11.0
  npm: 11.6.1
  Yarn: 1.22.22
  pnpm: 9.15.5
Relevant Packages:
  next: 16.1.1 // Latest available version is detected (16.1.1).
  eslint-config-next: N/A
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A
RAW_BUFFERClick to expand / collapse

Link to the code that reproduces this issue

https://github.com/DRoet/turbo-treeshake-bug

To Reproduce

Create project with client component that imports large .ts file with loads of enum definitions that are not being used. (see listed repository

  1. In the listed repository, run next build
  2. check the Turbopack bundle output using the new analyze command: next experimental-analyze
  3. large-utility.ts will be listed as ~20kb, none of the unused enums are stripped

Current vs. Expected behavior

I would expect the unused enums to be stripped from the final bundle just like next build --webpack

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 63146
  Available CPU cores: 16
Binaries:
  Node: 24.11.0
  npm: 11.6.1
  Yarn: 1.22.22
  pnpm: 9.15.5
Relevant Packages:
  next: 16.1.1 // Latest available version is detected (16.1.1).
  eslint-config-next: N/A
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Turbopack

Which stage(s) are affected? (Select all that apply)

next build (local)

Additional context

In our large repository we have a lot of GraphQL-Codegen with enums, so in our case its adding ~300kb to the final output compared to webpack

extent analysis

TL;DR

The issue can be mitigated by using a different build configuration or exploring tree-shaking options in Turbopack.

Guidance

  • Investigate the next build configuration to see if there are any options that can be used to enable tree-shaking for enums.
  • Compare the build configurations between next build and next build --webpack to identify any differences that may be causing the issue.
  • Consider using a custom Webpack configuration with Turbopack to enable enum tree-shaking.
  • Review the large-utility.ts file to see if there are any specific patterns or structures that may be preventing tree-shaking from working correctly.

Example

No specific code example is provided as the issue is related to build configuration and tree-shaking behavior.

Notes

The issue may be specific to the combination of Next.js, Turbopack, and TypeScript versions being used. Further investigation is needed to determine the root cause and find a suitable solution.

Recommendation

Apply workaround: The best course of action is to explore different build configurations and tree-shaking options in Turbopack to mitigate the issue, as upgrading to a fixed version is not clearly implied.

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