Not working eslintrc.json in Nextjs 15

[YouJun-IWON]

Link to the code that reproduces this issue

https://github.com/YouJun-IWON/My_Nextjs15

To Reproduce

1. set .eslintrc.json 2. check page.tsx 3. I don't see error messages for unused variables.

Current vs. Expected behavior

I expected to see error messages for unused variables. But I can't see any error.

If I install eslint@8.57.0 I can show error in page.tsx code.

Provide environment information

{
  "name": "prettier-eslint-husky-setting",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "next dev --turbopack",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  },
  "dependencies": {
    "next": "15.0.2",
    "react": "19.0.0-rc-02c0e824-20241028",
    "react-dom": "19.0.0-rc-02c0e824-20241028"
  },
  "devDependencies": {
    "@ianvs/prettier-plugin-sort-imports": "^4.3.1",
    "@types/node": "^20",
    "@types/react": "^18",
    "@types/react-dom": "^18",
    "@typescript-eslint/parser": "^8.12.2",
    "eslint": "^9.13.0",
    "eslint-config-next": "^15.0.2",
    "eslint-config-prettier": "^9.1.0",
    "eslint-plugin-tailwindcss": "^3.17.5",
    "eslint-plugin-unused-imports": "^4.1.4",
    "postcss": "^8",
    "prettier": "^3.3.3",
    "prettier-plugin-tailwindcss": "^0.6.8",
    "tailwindcss": "^3.4.1",
    "typescript": "^5"
  }
}

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

create-next-app, Linting

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

next dev (local)

Additional context

No response

[stefanprobst]

eslint v9 no longer supports json configs.

[YouJun-IWON]

@stefanprobst So, Why Nextjs 15 have eslintrc.json file?

[stefanprobst]

Why Nextjs 15 have eslintrc.json file?

create-next-app still has eslint pinned to v8 AFAICS.

[MonstraG]

And here is the issue from last week about create-next-app using eslint 8

#71763

[danielalves96]

Next.js 15 introduced changes to ESLint configuration. To simplify the setup and ensure ESLint and Prettier work correctly, I created a CLI that automates everything.

🔗 NPM: eslint-prettier-next-15
💻 GitHub: danielalves96/eslint-prettier-next-15

You can install and run it, and it will configure everything properly. Plus, you can customize the setup as needed. Hope this helps! 🚀