ESLint flat config for next.js. But incomplete yet. See: https://github.com/vercel/next.js/discussions/49337#discussioncomment-7588601

eslint.config.js

import nextPlugin from '@next/eslint-plugin-next'
import tsPlugin from '@typescript-eslint/eslint-plugin'
import tsParser from '@typescript-eslint/parser'
import prettierConfig from 'eslint-config-prettier'
import importPlugin from 'eslint-plugin-import'
import prettierPlugin from 'eslint-plugin-prettier'
import reactPlugin from 'eslint-plugin-react'
import hooksPlugin from 'eslint-plugin-react-hooks'

/** @type {import('eslint').Linter.FlatConfig[]} */
const config = [
  {
    // Put global `ignores` in the first item of config list // https://www.raulmelo.me/en/blog/migration-eslint-to-flat-config#no-more-eslintignore
    ignores: ['next-env.d.ts', '.next/**', 'out/**', '**/*.min.js'],
  },
  {
    plugins: {
      react: reactPlugin,
    },
    rules: {
      ...reactPlugin.configs.recommended.rules,
      ...reactPlugin.configs['jsx-runtime'].rules,
    },
    settings: {
      react: {
        version: 'detect', // Fix: Warning: React version not specified in eslint-plugin-react settings. See https://github.com/jsx-eslint/eslint-plugin-react#configuration
      },
    },
  },
  {
    plugins: {
      'react-hooks': hooksPlugin,
    },
    rules: hooksPlugin.configs.recommended.rules,
  },
  {
    plugins: {
      '@next/next': nextPlugin,
    },
    rules: {
      ...nextPlugin.configs.recommended.rules,
      ...nextPlugin.configs['core-web-vitals'].rules,
    },
  },
  prettierConfig,
  {
    plugins: {
      'import': importPlugin,
      'prettier': prettierPlugin,
      '@typescript-eslint': tsPlugin,
    },
    rules: {
      '@typescript-eslint/consistent-type-imports': ['warn', {disallowTypeAnnotations: false}],
      '@typescript-eslint/no-inferrable-types': 'warn',
      '@typescript-eslint/no-unused-vars': [
        'warn',
        {
          ignoreRestSiblings: true,
          destructuredArrayIgnorePattern: '^_',
        },
      ],
      '@typescript-eslint/no-explicit-any': 'warn',
      '@typescript-eslint/ban-types': 'warn',
      'prefer-const': 'warn',
      'no-useless-return': 'warn',
      'no-sequences': ['warn', {allowInParentheses: false}],
      'quote-props': ['warn', 'consistent-as-needed'],
      'dot-notation': 'warn',
      'spaced-comment': ['warn', 'always', {block: {balanced: true}}],
      'object-shorthand': 'warn',
      'no-empty-pattern': 'warn',
      'no-console': [
        'warn',
        {
          allow: Object.keys(console).filter((method) => method !== 'log'), // Allow everything except `console.log()`
        },
      ],
      'prefer-promise-reject-errors': ['error', {allowEmptyReject: true}],
      'react/jsx-filename-extension': ['error', {allow: 'as-needed', extensions: ['.jsx', '.tsx']}],
      'react/self-closing-comp': 'warn',
      'react/function-component-definition': ['error', {namedComponents: 'function-declaration'}],
      'react/jsx-curly-brace-presence': ['warn', {props: 'never', children: 'never'}],
      'react/no-unescaped-entities': 'off',
      'react/jsx-key': 'warn',
      'arrow-body-style': ['warn', 'as-needed'],
      'prefer-arrow-callback': ['error', {allowNamedFunctions: true}],
      'import/extensions': [
        'warn',
        'never',
        {
          css: 'always',
          json: 'always',
          svg: 'always',
          png: 'always',
          webp: 'always',
          graphql: 'always',
        },
      ],
      'import/first': 'warn',
      'prettier/prettier': 'warn',
    },
  },
  {
    files: ['**/*.ts', '**/*.tsx'],
    languageOptions: {
      parser: tsParser,
      // parserOptions: {
      //   ecmaFeatures: {modules: true, jsx: true},
      //   ecmaVersion: 'latest',
      //   project: './tsconfig.json',
      // },
    },
  },
]

export default config