Unable to override transformIgnorePatterns in next/jest

[czebe]

Verify canary release

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

Provide environment information

Operating System:
  Platform: darwin
  Arch: x64
  Version: Darwin Kernel Version 21.2.0: Sun Nov 28 20:28:54 PST 2021; root:xnu-8019.61.5~1/RELEASE_X86_64
Binaries:
  Node: 16.14.0
  npm: 8.3.1
  Yarn: 1.22.17
  pnpm: N/A
Relevant packages:
  next: 12.1.1-canary.2
  react: 17.0.2
  react-dom: 17.0.2

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

Some libraries ship es6 code and require to use next-transpile-modules.

It could be easy to transpile these by specifiying in transformIgnorePatterns, but the default config is not allowing overrides.

next.js/packages/next/build/jest/jest.ts

Line 118 in cc5345b

'/node_modules/',

Expected Behavior

Fully replace transformIgnorePatterns if it's specified in resolvedJestConfig.

To Reproduce

N/A

[ijjk]

Hi, I'm not sure we should completely throw away the default transformIgnorePatterns if one is provided since this could accidentally cause .next and all of node_modules to be transformed. Instead you can augment the built config e.g.

const nextJest = require('next/jest')

const createJestConfig = nextJest({
  // Provide the path to your Next.js app to load next.config.js and .env files in your test environment
  dir: './',
})

// Add any custom config to be passed to Jest
const customJestConfig = {
  // Add more setup options before each test is run
  // setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
  // if using TypeScript with a baseUrl set to the root directory then you need the below for alias' to work
  moduleDirectories: ['node_modules', '<rootDir>/'],
  testEnvironment: 'jest-environment-jsdom',
}

module.exports = async (...args) => {
  const fn = createJestConfig(customJestConfig)
  const res = await fn(...args)
  
  res.transformIgnorePatterns = res.transformIgnorePatterns.map(pattern => {
    if (pattern === '/node_modules/') {
      return '/node_modules(?!/excluded-module)/'
    }
    return pattern
  })
  
  return res
}

[davidcalhoun]

Thanks for the code sample, it's running great here!

Note that right now it's unexpected that some options in customJestConfig work (like setupFilesAfterEnv and testEnvironment) while others don't (transformIgnorePatterns). Probably makes sense to add this caveat to these docs: https://nextjs.org/docs/testing#setting-up-jest-with-the-rust-compiler

[wadehammes]

Typescript is not a big fan of the (...args), do you know what they should be typed for this?

[ChrisVilches]

This is the only workaround that worked for me to convert a .js file in node_modules with non-standard syntax.