eslint.config.mjs

import 'eslint-plugin-prettier';
import { FlatCompat } from '@eslint/eslintrc';
import js from '@eslint/js';
import tsParser from '@typescript-eslint/parser';
import { defineConfig, globalIgnores } from 'eslint/config';
import licenseHeader from 'eslint-plugin-license-header';
import preferArrow from 'eslint-plugin-prefer-arrow';
import simpleImportSort from 'eslint-plugin-simple-import-sort';
import globals from 'globals';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import prettierConfig from './prettier.config.mjs';
import unusedImports from 'eslint-plugin-unused-imports';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const compat = new FlatCompat({
    baseDirectory: __dirname,
    recommendedConfig: js.configs.recommended,
    allConfig: js.configs.all,
});

const additionalIgnorePatterns = process.env.additionalIgnorePatterns;
const overrideIgnorePatterns = process.env.overrideIgnorePatterns;
const optInRules = process.env.optInRules != null ? process.env.optInRules.split(',') : [];

const optInFunctionReturnType = 'explicit-function-return-type';

const ignores = globalIgnores(
    overrideIgnorePatterns != null
        ? overrideIgnorePatterns.split(',')
        : [
            '**/dist/**/*',
            '**/docs/**/*',
            '**/node_modules/**/*',
            ...(additionalIgnorePatterns != null ? additionalIgnorePatterns.split(',') : []),
        ],
);

const apacheLicenseHeader = `/* Morgan Stanley makes this available to you under the Apache License,
 * Version 2.0 (the "License"). You may obtain a copy of the License at
 *      http://www.apache.org/licenses/LICENSE-2.0.
 * See the NOTICE file distributed with this work for additional information
 * regarding copyright ownership. Unless required by applicable law or agreed
 * to in writing, software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions
 * and limitations under the License. */`;

const rules = {
    'lines-between-class-members': ['error', 'always', { exceptAfterSingleLine: true }],
    'no-unused-vars': 'off', // typescript already warns about unused but allows some like _someVar
    '@typescript-eslint/no-unused-vars': 'off', // typescript already warns about unused but allows some like _someVar
    '@typescript-eslint/no-explicit-any': 'off', // 'spose... ¯\_(ツ)_/¯
    '@typescript-eslint/explicit-module-boundary-types': 'off', // typescript already warns about unused but allows some like _someVar
    'no-case-declarations': 'off', // prevents declaring variables within a case statement
    '@typescript-eslint/no-inferrable-types': 'off', // forces removal of types for simple assignments like const myVar: string = "someString";
    '@typescript-eslint/no-non-null-assertion': 'off', // allow bangs :'(
    '@typescript-eslint/no-non-null-asserted-optional-chain': 'off', // allows bangs at the end of optional chaining :'(
    '@typescript-eslint/explicit-member-accessibility': ['error', { overrides: { constructors: 'no-public' } }], // checks for public / private
    '@typescript-eslint/explicit-function-return-type': ['warn', { allowExpressions: true }], // warn only about missing return types
    '@typescript-eslint/prefer-as-const': 'off', // we don't really care if a const is marked as a const
    '@typescript-eslint/no-empty-object-type': 'off', // we use empty interfaces as markers for functionality
    'no-sequences': ['error', { allowInParentheses: false }], // prevents weird multiple expressions separated by comma
    'sort-imports': 'off', // disabled default sorting as we have better option
    'import/no-unresolved': 'off',
    'simple-import-sort/imports': [
        'error',
        {
            groups: [['^\\u0000', '^@?\\w', '^', '^\\.']], // disable blank lines between groups
        },
    ], // alphabetically sorts imports
    'import/no-duplicates': 'error', // removes duplicate imports
    'prettier/prettier': ['error', prettierConfig], // runs prettier
    'license-header/header': ['error', [apacheLicenseHeader]], // OSS license header
    'unused-imports/no-unused-imports': 'error', // removes unused imports
};

if (typeof process.env.BUILD_TYPE === 'string' && process.env.BUILD_TYPE.toLowerCase() === 'release') {
    rules['import/no-cycle'] = 'error';
}

if (optInRules.indexOf(optInFunctionReturnType) >= 0) {
    rules['@typescript-eslint/explicit-function-return-type'] = ['error', { allowExpressions: true }];
}

export default defineConfig([
    ignores,
    {
        extends: compat.extends(
            'eslint:recommended',
            'plugin:@typescript-eslint/recommended',
            'plugin:prettier/recommended',
            'plugin:import/recommended',
            'plugin:import/typescript',
        ),

        plugins: {
            'prefer-arrow': preferArrow,
            'simple-import-sort': simpleImportSort,
            'license-header': licenseHeader,
            "unused-imports": unusedImports
        },

        languageOptions: {
            globals: {
                ...globals.browser,
                ...globals.node,
            },

            parser: tsParser,
        },

        rules,
    },
    {
        files: ['**/*.js'],

        rules: {
            '@typescript-eslint/no-require-imports': 'off',
            '@typescript-eslint/no-var-requires': 'off',
            '@typescript-eslint/explicit-function-return-type': 'off',
        },
    },
    {
        files: ['**/*.spec.ts'],

        rules: {
            '@typescript-eslint/no-require-imports': 'off',
            '@typescript-eslint/no-non-null-assertion': 'off',
            '@typescript-eslint/no-empty-function': 'off',
            '@typescript-eslint/ban-types': 'off',
            '@typescript-eslint/explicit-function-return-type': 'off',
        },
    },
    {
        files: ['**/*.config.js', '**/*.config.ts', '**/*.cjs', '**/*.mjs'],

        rules: {
            'license-header/header': 'off',
            '@typescript-eslint/no-require-imports': 'off',
        },
    },
]);