Dynamic Code Evaluation (e. g. 'eval', 'new Function') not allowed in Middleware pages/_middleware even if I don't use functions like eval and new Function

[8byr0]

Verify canary release

• I verified that the issue exists in Next.js canary release

Provide environment information

Operating System:
Platform: darwin
Arch: arm64
Version: Darwin Kernel Version 21.3.0: Wed Jan 5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_ARM64_T6000
Binaries:
Node: 14.18.2
npm: 6.14.15
Yarn: 1.22.17
pnpm: N/A
Relevant packages:
next: 12.1.0
react: 17.0.2
react-dom: 17.0.2

What browser are you using? (if relevant)

N/A

How are you deploying your application? (if relevant)

N/A

Describe the Bug

next start and next dev work fine, but next build throws the following error:

Dynamic Code Evaluation (e. g. 'eval', 'new Function') not allowed in Middleware pages/_middleware

This issue occurs even with a very simple middleware.

Expected Behavior

It should not trigger this error.

To Reproduce

Run a nextjs project with the following .babelrc

// .babelrc
{
  "presets": ["next/babel", "@babel/preset-typescript"],
  "plugins": ["relay", "istanbul]
}

[8byr0]

I came across this issue and found a few similar ones reported:

• Dynamic Code Evaluation (e. g. 'eval', 'new Function') not allowed in Middleware pages/_middleware even if I don't use functions like eval and new Function #32608
• Dynamic Code Evaluation (e. g. 'eval', 'new Function') not allowed in Middleware pages/_middleware even if my middleware is quite simple #32532

There have been solutions proposed in there like disabling istanbul for a given file (#32608 (comment)) but since istanbul is used in testing environment I wanted to share another solution based on babel env feature:

// .babelrc
{
  "presets": ["next/babel", "@babel/preset-typescript"],
  "plugins": ["relay"],
  "env": {
    "test": {
      // override plugin configuration for testing env
      "plugins": ["relay", "istanbul"]
    }
  }
}

[github-actions]

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