nextjs - 💡(How to fix) Fix Next SWC Jest transform incorrectly rewrites import attribute keyword in ESM mode [1 comments, 1 participants]

Link to the code that reproduces this issue

https://github.com/nlwillia/import-attributes

To Reproduce

1. npm install
2. npm run test
3. Note that the test has failed with SyntaxError: Unexpected identifier 'assert' in the log.
4. node app/index.ts
5. Note that the import is resolved and a result prints.

Current vs. Expected behavior

My project uses import attributes which originally used the keyword "assert" but have since changed to use the keyword "with". Node 24 does not support the keyword "assert".

The modern "with" syntax works in typescript code in a Next app, but it is failing in a Jest-based test because Next is inserting its own transform based on SWC, and when tests are run in ESM mode Next's forced config is setting an experimental option emitAssertForImportAttributes: true that replaces the "with" keyword with the old "assert".

The relevant line in Next's transform code is here. There's no way to supersede this option that I can see. Adding a .swcrc file doesn't help.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 65448
  Available CPU cores: 16
Binaries:
  Node: 24.11.1
  npm: 11.6.2
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.1.0-canary.20 // Latest available version is detected (16.1.0-canary.20).
  eslint-config-next: N/A
  react: 19.2.2
  react-dom: 19.2.2
  typescript: 5.9.3
Next.js Config:
  output: N/A

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

Testing

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

next dev (local)

Additional context

Rough stack of where the hardwired transform SWC options are hit.

getBaseSWCOptions(), options.ts:116 getBaseSWCOptions(), options.ts:327 process(), jest-transformer.ts:87 transformSourceAsync(), index.js:462 processTicksAndRejections(), task_queues:103 Async call from await _transformAndBuildScriptAsync(), index.js:488 transformAsync(), index.js:542 transformFileAsync(), index.js:1302 loadEsmModule(), index.js:503 unstable_importModule(), index.js:694 processTicksAndRejections(), task_queues:103 Async call from await jestAdapter(), runner.js:82 processTicksAndRejections(), task_queues:103 Async call from await runTestInternal(), index.js:275 processTicksAndRejections(), task_queues:103 Async call from await processTicksAndRejections(), task_queues:103 Async call from await processTicksAndRejections(), task_queues:103 Async call from await processTicksAndRejections(), task_queues:103 Async call from await runTest(), index.js:343 anonymous(), index.js:499 processTicksAndRejections(), task_queues:103 Async call from await processTicksAndRejections(), task_queues:103 Async call from Promise.then anonymous(), index.js:494 anonymous(), index.js:23 run(), index.js:23 anonymous(), index.js:45 processTicksAndRejections(), task_queues:103 Async call from await enqueue(), index.js:47 anonymous(), index.js:51 generator(), index.js:50 anonymous(), index.js:494 #createInBandTestRun(), index.js:494 runTests(), index.js:489 scheduleTests(), index.js:1140 processTicksAndRejections(), task_queues:103