[BUG]: Next.js 15 + middleware causes `__import_unsupported` error

[dario-piotrowicz]

Describe the bug

If I have an Next.js app that is on Next.js 15 and has a middleware, the adapter can build the application but at runtime the application throws a __import_unsupported error:

Steps to reproduce

• Create a new Next.js 15 application
• Install the adapter (the experimental release)
• add a middleware file
• build and preview the application
• navigate to the application's url to see the error

Minimal reproduction: https://github.com/dario-piotrowicz/open-next-15-middleware-experimental-repro

Expected behavior

The application should just work

@opennextjs/cloudflare version

https://pkg.pr.new/@opennextjs/cloudflare@experimental

Node.js version

20

Wrangler version

3

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.1.0: Thu Oct 10 21:03:15 PDT 2024; root:xnu-11215.41.3~2/RELEASE_ARM64_T6000
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 20.11.0
  npm: 10.2.4
  Yarn: 1.22.19
  pnpm: 9.12.1
Relevant Packages:
  next: 15.1.0 // Latest available version is detected (15.1.0).
  eslint-config-next: 14.2.5
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.2
Next.js Config:
  output: N/A

Additional context

#141 implements a simple fix for this

but:

• the fix should be done properly with AST manipulation
• we should understand better why this issue gets triggered and if the proposed patch is the appropriate solution

[conico974]

We already have a fix for this in aws but at the moment it's not applied to cloudflare https://github.com/opennextjs/opennextjs-aws/blob/697681bf9ce25212ce4e2e94d886ca425428280d/packages/open-next/src/build/edge/createEdgeBundle.ts#L141-L147. Just moving this a few line up should be enough.

This happens when the middleware runs in the same place as the main handler.
They use defineProperty for __import_unsupported both in the middleware and in the main server but they define it with configurable:false

[dario-piotrowicz]

Great, thanks for the context @conico974 😄

Ah ok, so you're saying that this is a fix to be made in the aws package and that we'll then inherit right? 🙂
I'm happy to give it a go unless you want to take it on 😄

[conico974]

I could do it tomorrow if you want, but if you want to do it in the meantime feel free to do so

[dario-piotrowicz]

I could do it tomorrow if you want, but if you want to do it in the meantime feel free to do so

opennextjs/opennextjs-aws#678 🙂

[dario-piotrowicz]

Reopening until this is merged to main

[vicb]

Reopening until this is merged to main

Added to the Done (experimental branch) column