Sourcemaps broken for next/dist files in Yarn PnP mode (webpack)

[WooWan]

Link to the code that reproduces this issue

https://github.com/WooWan/yarn-pnp-sourcemap-repro/tree/main

To Reproduce

1. Start the application in development (yarn dev)
2. Open Chrome DevTools → Sources tab
3. Look for next/dist/client/components/app-router.js
4. Instead of seeing original .ts source files, the bundled .js files are shown

Current vs. Expected behavior

Current: In Yarn PnP mode, DevTools shows .js files instead of original .ts sources for Next.js internal runti
+me files (next/dist/client/, next/dist/shared/lib/, next/dist/pages/). inputSourceMap is not passed to the SWC
+ loader, so source map chaining is broken.

Expected: DevTools should show .ts source files, same as non-PnP mode.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.3.0: Wed Jan 28 20:53:15 PST 2026; root:xnu-12377.81.4~5/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 10
Binaries:
  Node: 24.6.0
  npm: 11.5.1
  Yarn: 4.12.0
  pnpm: N/A
Relevant Packages:
  next: 16.1.6
  eslint-config-next: N/A
  react: 19.2.3
  react-dom: 19.2.3
  typescript: 5.9.3
Next.js Config:
  output: N/A

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

Webpack, SWC

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

next dev (local), next build (local)

Additional context

No response

[darshjme-codes]

Triage: Sourcemaps broken for next/dist files in Yarn Berry → affects debugging | Labels applied: SWC ✓ | Additional: Yarn, DevEx