eslint.config.mjs

// @ts-check

import eslint from '@eslint/js';
import eslintConfigPrettier from 'eslint-config-prettier';
import eslintPluginJest from 'eslint-plugin-jest';
import * as eslintPluginJestFormatting from 'eslint-plugin-jest-formatting';
import eslintPluginUnicorn from 'eslint-plugin-unicorn';
import typescriptEslint from 'typescript-eslint';

export default typescriptEslint.config(
  eslint.configs.recommended,
  ...typescriptEslint.configs.strictTypeChecked,
  ...typescriptEslint.configs.stylisticTypeChecked,
  /** @type {any} */ (eslintPluginUnicorn.configs['flat/recommended']),
  eslintConfigPrettier,
  {
    languageOptions: {
      ecmaVersion: 'latest',
      parserOptions: {
        project: true,
      },
    },
    rules: {
      // Core ESLint rules
      'accessor-pairs': 'error',
      'camelcase': [
        'error',
        {
          allow: ['Vue2_6', 'Vue2_7'],
        },
      ],
      'consistent-return': 'error',
      'curly': ['error', 'all'],
      'dot-notation': 'error',
      'eqeqeq': 'error',
      'getter-return': 'error',
      'grouped-accessor-pairs': ['error', 'getBeforeSet'],
      'guard-for-in': 'error',
      'no-array-constructor': 'error',
      'no-bitwise': 'error',
      'no-constant-binary-expression': 'error',
      'no-constant-condition': 'error',
      'no-else-return': ['error', { allowElseIf: false }],
      'no-irregular-whitespace': 'error',
      'no-lonely-if': 'error',
      'no-loop-func': 'error',
      'no-mixed-operators': 'error',
      'no-new-object': 'error',
      'no-prototype-builtins': 'error',
      'no-return-assign': 'error',
      'no-return-await': 'error',
      'no-shadow': 'off', // replaced by @typescript-eslint/no-shadow
      'no-template-curly-in-string': 'error',
      'no-unsafe-optional-chaining': [
        'error',
        { disallowArithmeticOperators: true },
      ],
      'object-shorthand': ['error', 'always', { avoidQuotes: true }],
      'prefer-arrow-callback': 'error',
      'prefer-template': 'error',
      'quotes': [
        'error',
        'single',
        { avoidEscape: true, allowTemplateLiterals: false },
      ],
      'radix': 'error',
      'spaced-comment': 'error',

      // eslint-plugin-unicorn
      'unicorn/filename-case': 'off',
      'unicorn/no-null': 'off',
      'unicorn/no-useless-undefined': 'off', // conflicts with consistent-return
      'unicorn/prevent-abbreviations': [
        'warn',
        {
          replacements: {
            prop: false,
          },
        },
      ],

      // @typescript-eslint/eslint-plugin
      '@typescript-eslint/consistent-type-exports': 'error',
      '@typescript-eslint/consistent-type-imports': 'error',
      '@typescript-eslint/explicit-module-boundary-types': 'error',
      '@typescript-eslint/no-confusing-void-expression': [
        'error',
        {
          ignoreVoidOperator: true,
          ignoreArrowShorthand: true,
        },
      ],
      '@typescript-eslint/no-explicit-any': 'off', // needed for Vue types compatibility
      '@typescript-eslint/no-extraneous-class': 'off',
      '@typescript-eslint/no-shadow': [
        'warn',
        { ignoreOnInitialization: true },
      ],
      '@typescript-eslint/no-unsafe-unary-minus': 'error',
      '@typescript-eslint/no-useless-template-literals': 'error',
      '@typescript-eslint/prefer-enum-initializers': 'error',
      '@typescript-eslint/prefer-readonly': 'error',
      '@typescript-eslint/promise-function-async': 'error',
      '@typescript-eslint/sort-type-constituents': 'warn',
      '@typescript-eslint/switch-exhaustiveness-check': 'error',
    },
  },
  { ignores: ['**/*.json', 'node_modules', 'dist'] },
  {
    files: ['eslint.config.mjs'],
    rules: {
      // less strict rules for ESLint config while some ESLint plugins don't provide proper types
      '@typescript-eslint/no-unsafe-argument': 'off',
      '@typescript-eslint/no-unsafe-assignment': 'off',
      '@typescript-eslint/no-unsafe-call': 'off',
      '@typescript-eslint/no-unsafe-member-access': 'off',
    },
  },
  {
    files: ['tests/**/*.spec.ts'],
    plugins: {
      'jest': eslintPluginJest,
      'jest-formatting': eslintPluginJestFormatting,
    },
    rules: {
      ...eslintPluginJest.configs['flat/recommended'].rules,
      ...eslintPluginJest.configs['flat/style'].rules,
      ...eslintPluginJestFormatting.configs.recommended.overrides[0].rules,

      // additional Jest rules
      'jest/consistent-test-it': 'error',
      'jest/no-confusing-set-timeout': 'error',
      'jest/no-duplicate-hooks': 'error',
      'jest/no-test-return-statement': 'error',
      'jest/no-untyped-mock-factory': 'error',
      'jest/prefer-called-with': 'error',
      'jest/prefer-comparison-matcher': 'warn',
      'jest/prefer-equality-matcher': 'warn',
      'jest/prefer-expect-resolves': 'warn',
      'jest/prefer-hooks-on-top': 'warn',
      'jest/prefer-importing-jest-globals': 'error',
      'jest/prefer-mock-promise-shorthand': 'error',
      'jest/prefer-spy-on': 'warn',
      'jest/prefer-strict-equal': 'warn',
      'jest/require-to-throw-message': 'warn',
      'jest/require-top-level-describe': 'warn',

      // less strict other rules
      '@typescript-eslint/no-non-null-assertion': 'off',
      '@typescript-eslint/no-unsafe-argument': 'off',
      '@typescript-eslint/no-unsafe-assignment': 'off',
      '@typescript-eslint/no-unsafe-call': 'off',
    },
  },
);