Next.js does not pick up external eslint config

[EliasVal]

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/serene-napier-go8s7s

To Reproduce

1. Set up monorepo (pnpm workspaces)
2. Have a root eslint config file (with settings.next.rootDir set as per docs)
3. Run next lint

Current vs. Expected behavior

Currently, when running next lint with the above reproduction steps, next tries to go through eslint config setup.
Expected Behaviour: For next lint to pick up the root eslint config, possibly through an option in next.config.js

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 32457
  Available CPU cores: 24
Binaries:
  Node: 20.12.2
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 15.0.0-canary.53 // There is a newer canary version (15.0.0-canary.59) available, please upgrade!
  eslint-config-next: 15.0.0-canary.54
  react: 19.0.0-rc-58af67a8f8-20240628
  react-dom: 19.0.0-rc-58af67a8f8-20240628
  typescript: 5.4.5
Next.js Config:
  output: N/A

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

Developer Experience, Linting

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

next dev (local), next build (local), next start (local)

Additional context

Unfortunately, I can't link to a reproduction environment, since company policy is tight on keeping the repo private, and setting a monorepo again is gonna be hell for me 😅

[EliasVal]

I think it'd be a good idea to display the file structure of the repo:

/
  - apps
    - next-project
    
  eslint.config.mjs
  tsconfig.json

[devjiwonchoi]

Hi, are you using ESLint v9 newly added eslint.config.mjs?

[EliasVal]

Hi, yes I am. Now it says that "⚠ The Next.js plugin was not detected in your ESLint configuration. See https://nextjs.org/docs/basic-features/eslint#migrating-existing-config".

This is (part of) my eslint.config.mjs:

export default [
  includeIgnoreFile(gitignorePath)
  , ...compat.extends(
    'plugin:react/recommended',
    'plugin:@typescript-eslint/recommended',
    'plugin:@next/next/recommended',
    'plugin:jsx-a11y/recommended',
    'plugin:react-hooks/recommended',
    'plugin:tailwindcss/recommended'
  ), {
    plugins: {
      react,
      '@typescript-eslint': typescriptEslint,
      'simple-import-sort': simpleImportSort,
      'jsx-a11y': jsxA11Y,
      '@next/next': nextEslintPluginNext,
      '@stylistic': stylistic,
      'unused-imports': unusedImports,
      'node-import': nodeImport,
      'react-compiler': reactCompiler,
    }
  }
]

[devjiwonchoi]

We shipped support for ESLint v9 at #71218 https://github.com/vercel/next.js/releases/tag/v15.0.0-canary.191 could you check if it works on that version? The next release will include this change.

[EliasVal]

I am using ESLint v9 in my project with latest canary, just haven't updated the reproduction repo

[devjiwonchoi]

You mean installed version >= v15.0.0-canary.191 (release) does not pick up eslint.config.mjs?

[EliasVal]

That's correct! I have Next.js v15.0.0-canary.191, along with @next/eslint-plugin-next and it does not pick up eslint.config.mjs in the root of the monorepo

[aXenDeveloper]

I have the same issue. See: https://github.com/VitNode/vitnode/actions/runs/11342674726/job/31543606622

[EliasVal]

I'm getting that exact error, for now, I opted into not running next lint, setting eslint.ignoreDuringBuilds: true in the next config file, and instead just running ESlint directly

[devjiwonchoi]

Thank you so much for reporting! Identified the issue, will fix ASAP!