.eslintrc.json

{
  "root": true,
  "parser": "@babel/eslint-parser",
  "plugins": ["react", "react-hooks", "jest", "import", "jsdoc"],
  "env": {
    "browser": true,
    "commonjs": true,
    "es6": true,
    "node": true
  },
  "parserOptions": {
    "requireConfigFile": false,
    "sourceType": "module",
    "ecmaFeatures": {
      "jsx": true
    },
    "babelOptions": {
      "presets": ["next/babel"],
      "caller": {
        // Eslint supports top level await when a parser for it is included. We enable the parser by default for Babel.
        "supportsTopLevelAwait": true
      }
    }
  },
  "settings": {
    "react": {
      "version": "detect"
    },
    "import/internal-regex": "^next/"
  },
  "overrides": [
    {
      "files": ["test/**/*.js", "test/**/*.ts", "**/*.test.ts"],
      "extends": ["plugin:jest/recommended"],
      "rules": {
        "jest/expect-expect": "off",
        "jest/no-disabled-tests": "off",
        "jest/no-conditional-expect": "off",
        "jest/valid-title": "off",
        "jest/no-interpolation-in-snapshots": "off",
        "jest/no-export": "off"
      }
    },
    { "files": ["**/__tests__/**"], "env": { "jest": true } },
    {
      "extends": [
        "plugin:@typescript-eslint/recommended",
        "plugin:@typescript-eslint/stylistic"
      ],
      "files": ["**/*.ts", "**/*.tsx"],
      "parser": "@typescript-eslint/parser",
      "parserOptions": {
        "sourceType": "module",
        "warnOnUnsupportedTypeScriptVersion": false
      },
      "plugins": ["@typescript-eslint"],
      "rules": {
        // Todo: investigate, for each of these rules, whether we want them.
        "@typescript-eslint/array-type": "off",
        "@typescript-eslint/ban-ts-comment": "off",
        "@typescript-eslint/ban-tslint-comment": "off",
        "@typescript-eslint/ban-types": "off",
        "@typescript-eslint/class-literal-property-style": "off",
        "@typescript-eslint/consistent-generic-constructors": "off",
        "@typescript-eslint/consistent-indexed-object-style": "off",
        "@typescript-eslint/consistent-type-definitions": "off",
        "@typescript-eslint/no-empty-function": "off",
        "@typescript-eslint/no-namespace": "off",
        "@typescript-eslint/no-shadow": "off",
        "@typescript-eslint/no-empty-interface": "off",
        "@typescript-eslint/no-explicit-any": "off",
        "@typescript-eslint/no-inferrable-types": "off",
        "@typescript-eslint/no-var-requires": "off",
        "@typescript-eslint/prefer-for-of": "off",
        "@typescript-eslint/prefer-function-type": "off",
        "@typescript-eslint/no-this-alias": "off",
        "@typescript-eslint/triple-slash-reference": "off",
        "no-var": "off",
        "prefer-const": "off",
        "prefer-rest-params": "off",
        "prefer-spread": "off",

        // These off- or differently-configured rules work well for us.
        "no-unused-expressions": "off",
        "@typescript-eslint/no-unused-expressions": [
          "error",
          {
            "allowShortCircuit": true,
            "allowTernary": true,
            "allowTaggedTemplates": true
          }
        ],
        "no-unused-vars": "off",
        "@typescript-eslint/no-unused-vars": [
          "warn",
          {
            "args": "none",
            "ignoreRestSiblings": true
          }
        ],
        "no-use-before-define": "off",
        "@typescript-eslint/no-use-before-define": [
          "warn",
          {
            "functions": true,
            "classes": true,
            "variables": true,
            "enums": true,
            "typedefs": true
          }
        ],
        "no-useless-constructor": "off",
        "@typescript-eslint/no-useless-constructor": "warn",
        "@typescript-eslint/prefer-literal-enum-member": "error"
      }
    },
    {
      "files": ["packages/**/*.tsx?"],
      "rules": {
        "jsdoc/no-types": "error",
        "jsdoc/no-undefined-types": "error"
      }
    },
    {
      "files": [
        "test/**/*",
        "examples/**/*",
        "packages/create-next-app/templates/**/*"
      ],
      "rules": { "react/react-in-jsx-scope": "off" }
    },
    {
      "files": ["examples/**/*"],
      "rules": {
        "@typescript-eslint/no-use-before-define": [
          "error",
          {
            "functions": true,
            "classes": true,
            "variables": true,
            "enums": true,
            "typedefs": true
          }
        ],
        "import/no-anonymous-default-export": [
          "error",
          {
            // React components:
            "allowArrowFunction": false,
            "allowAnonymousClass": false,
            "allowAnonymousFunction": false,

            // Non-React stuff:
            "allowArray": true,
            "allowCallExpression": true,
            "allowLiteral": true,
            "allowObject": true
          }
        ]
      }
    },
    {
      "files": ["packages/**"],
      "excludedFiles": ["packages/next/taskfile.js"],
      "rules": {
        "no-shadow": ["warn", { "builtinGlobals": false }],
        "import/no-extraneous-dependencies": [
          "error",
          { "devDependencies": false }
        ]
      }
    },
    {
      "files": ["packages/**/*.tsx", "packages/**/*.ts"],
      "rules": {
        // Note: you must disable the base rule as it can report incorrect errors
        "no-shadow": "off",
        "@typescript-eslint/no-shadow": ["warn", { "builtinGlobals": false }],
        "@typescript-eslint/no-unused-vars": [
          "warn",
          {
            "args": "all",
            "argsIgnorePattern": "^_",
            "ignoreRestSiblings": true
          }
        ]
      }
    },
    {
      "files": [
        "packages/eslint-plugin-next/**/*.js",
        "test/unit/eslint-plugin-next/**/*.test.ts"
      ],
      "extends": ["plugin:eslint-plugin/recommended"],
      "parserOptions": {
        "sourceType": "script"
      },
      "rules": {
        "eslint-plugin/prefer-replace-text": "error",
        "eslint-plugin/report-message-format": [
          "error",
          ".+\\. See: https://nextjs.org/docs/messages/[a-z\\-]+$"
        ],
        "eslint-plugin/require-meta-docs-description": [
          "error",
          {
            "pattern": ".+"
          }
        ],
        "eslint-plugin/require-meta-docs-url": "error"
      }
    }
  ],
  "rules": {
    "array-callback-return": "warn",
    "default-case": ["warn", { "commentPattern": "^no default$" }],
    "dot-location": ["warn", "property"],
    "eqeqeq": ["warn", "smart"],
    "new-parens": "warn",
    "no-array-constructor": "warn",
    "no-caller": "warn",
    "no-cond-assign": ["warn", "except-parens"],
    "no-const-assign": "warn",
    "no-control-regex": "warn",
    "no-delete-var": "warn",
    "no-dupe-args": "warn",
    "no-dupe-class-members": "warn",
    "no-dupe-keys": "warn",
    "no-duplicate-case": "warn",
    "no-empty-character-class": "warn",
    "no-empty-pattern": "warn",
    "no-eval": "warn",
    "no-ex-assign": "warn",
    "no-extend-native": "warn",
    "no-extra-bind": "warn",
    "no-extra-label": "warn",
    "no-fallthrough": "warn",
    "no-func-assign": "warn",
    "no-implied-eval": "warn",
    "no-invalid-regexp": "warn",
    "no-iterator": "warn",
    "no-label-var": "warn",
    "no-labels": ["warn", { "allowLoop": true, "allowSwitch": false }],
    "no-lone-blocks": "warn",
    "no-loop-func": "warn",
    "no-mixed-operators": [
      "warn",
      {
        "groups": [
          ["&", "|", "^", "~", "<<", ">>", ">>>"],
          ["==", "!=", "===", "!==", ">", ">=", "<", "<="],
          ["&&", "||"],
          ["in", "instanceof"]
        ],
        "allowSamePrecedence": false
      }
    ],
    "no-multi-str": "warn",
    "no-native-reassign": "warn",
    "no-negated-in-lhs": "warn",
    "no-new-func": "warn",
    "no-new-object": "warn",
    "no-new-symbol": "warn",
    "no-new-wrappers": "warn",
    "no-obj-calls": "warn",
    "no-octal": "warn",
    "no-octal-escape": "warn",
    "no-regex-spaces": "warn",
    "no-restricted-syntax": [
      "warn",
      "WithStatement",
      {
        "message": "substr() is deprecated, use slice() or substring() instead",
        "selector": "MemberExpression > Identifier[name='substr']"
      }
    ],
    "no-script-url": "warn",
    "no-self-assign": "warn",
    "no-self-compare": "warn",
    "no-sequences": "warn",
    "no-shadow-restricted-names": "warn",
    "no-sparse-arrays": "warn",
    "no-template-curly-in-string": "error",
    "no-this-before-super": "warn",
    "no-throw-literal": "warn",
    "no-undef": "error",
    "no-unexpected-multiline": "warn",
    "no-unreachable": "warn",
    "no-unused-expressions": [
      "error",
      {
        "allowShortCircuit": true,
        "allowTernary": true,
        "allowTaggedTemplates": true
      }
    ],
    "no-unused-labels": "warn",
    "no-unused-vars": [
      "warn",
      {
        "args": "none",
        "ignoreRestSiblings": true
      }
    ],
    "no-use-before-define": [
      "warn",
      {
        "functions": false,
        "classes": false,
        "variables": false
      }
    ],
    "no-useless-computed-key": "warn",
    "no-useless-concat": "warn",
    "no-useless-constructor": "warn",
    "no-useless-escape": "warn",
    "no-useless-rename": [
      "warn",
      {
        "ignoreDestructuring": false,
        "ignoreImport": false,
        "ignoreExport": false
      }
    ],
    "no-with": "warn",
    "no-whitespace-before-property": "warn",
    "react-hooks/exhaustive-deps": "warn",
    "require-yield": "warn",
    "rest-spread-spacing": ["warn", "never"],
    "strict": ["warn", "never"],
    "unicode-bom": ["warn", "never"],
    "use-isnan": "warn",
    "valid-typeof": "warn",
    "getter-return": "warn",
    "react/forbid-foreign-prop-types": ["warn", { "allowInPropTypes": true }],
    "react/jsx-no-comment-textnodes": "warn",
    "react/jsx-no-duplicate-props": "warn",
    "react/jsx-no-target-blank": "warn",
    "react/jsx-no-undef": "error",
    "react/jsx-pascal-case": [
      "warn",
      {
        "allowAllCaps": true,
        "ignore": []
      }
    ],
    "react/jsx-uses-react": "warn",
    "react/jsx-uses-vars": "warn",
    "react/no-danger-with-children": "warn",
    "react/no-deprecated": "warn",
    "react/no-direct-mutation-state": "warn",
    "react/no-is-mounted": "warn",
    "react/no-typos": "error",
    "react/react-in-jsx-scope": "error",
    "react/require-render-return": "error",
    "react/style-prop-object": "warn",
    "react-hooks/rules-of-hooks": "error",
    // "@typescript-eslint/non-nullable-type-assertion-style": "warn",
    "@typescript-eslint/prefer-as-const": "warn",
    "@typescript-eslint/no-redeclare": [
      "warn",
      { "builtinGlobals": false, "ignoreDeclarationMerge": true }
    ]
  }
}