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nextjs - ✅(Solved) Fix Duplicate SWC transform for use client components when React Compiler is disabled [1 pull requests, 1 participants]

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vercel/next.js#90248•Fetched 2026-04-08 00:20:30
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Fix Action

Fixed

PR fix notes

PR #90296: turbopack: pass layer as named query param to SWC transform context

Description (problem / solution / changelog)

Append layer to the filename passed to SWC (TransformContext) so plugins see e.g. app/page.tsx?layer=app-rsc, aligning with next-swc-loader. Use named param "layer=value" (Vite-style) for extensibility; use "&layer=..." when the path already has a query.

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Changed files

  • turbopack/crates/turbopack-ecmascript/src/lib.rs (modified, +7/-0)
  • turbopack/crates/turbopack-ecmascript/src/parse.rs (modified, +20/-2)
  • turbopack/crates/turbopack-ecmascript/src/webpack/parse.rs (modified, +1/-0)
  • turbopack/crates/turbopack-ecmascript/src/webpack/references.rs (modified, +1/-0)

Code Example

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.0.0: Wed Sep 17 21:41:45 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 25.2.1
  npm: 11.6.2
  Yarn: N/A
  pnpm: 10.13.0
Relevant Packages:
  next: 16.1.6 // Latest available version is detected (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
RAW_BUFFERClick to expand / collapse

Link to the code that reproduces this issue

https://github.com/canyon-project/nextjs16-swc-duplicate-compilation

To Reproduce

  1. pnpm i
  2. npm run build
  3. look .swc-plugin-stage-output

Current vs. Expected behavior

After testing the Next.js + Turbopack combination, we observed duplicate identical filenames appearing in the SWC AST during compilation. Our investigation identified that this behavior is inherent to Next.js' compilation workflow.
To address this ambiguity (consistent with Vite's pattern), we propose appending a layer query parameter to the filename passed to SWC (via TransformContext) — e.g., app/page.tsx?layer=app-rsc — to enable SWC plugins to distinguish between these duplicate entries.
For extensibility (aligned with next-swc-loader), we use a named parameter format:

  • Use ?layer=value for paths with no existing query string
  • Use &layer=... for paths that already contain a query string
<img width="425" height="269" alt="Image" src="https://github.com/user-attachments/assets/e67dd612-69a1-42b5-bd35-8e5a4847b46e" /> <img width="565" height="492" alt="Image" src="https://github.com/user-attachments/assets/22ce4793-50d8-4a14-93c6-2a3a7388f775" />

Expected behavior

<img width="541" height="417" alt="Image" src="https://github.com/user-attachments/assets/dec3ed40-59ab-43d5-ab56-652ccfdcfa05" />

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.0.0: Wed Sep 17 21:41:45 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 25.2.1
  npm: 11.6.2
  Yarn: N/A
  pnpm: 10.13.0
Relevant Packages:
  next: 16.1.6 // Latest available version is detected (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)

SWC

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

next build (local)

Additional context

extent analysis

Fix: Append a layer query‑parameter to the filename passed to SWC

Next.js (v16) feeds the same source file to SWC twice – once for the app layer and once for the rsc layer – without any way for a plugin to tell them apart.
The easiest, non‑breaking fix is to mutate the filename that reaches the SWC transform context:

// file: node_modules/next/dist/compiler/next-swc-loader.ts
// (or copy the file into your repo and point Next to it via a custom loader)

import type { TransformContext } from '@swc/core';

// Helper – add ?layer=… or &layer=… depending on existing query string
function withLayerQuery(original: string, layer: string): string {
  return original.includes('?')
    ? `${original}&layer=${layer}`
    : `${original}?layer=${layer}`;
}

// Patch the function that creates the TransformContext
export function createTransformContext(
  filename: string,
  source: string,
  // …other args
): TransformContext {
  // ---------------------------------------------------------

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