feat(eslint-config-base): fully incorporate eslint-config-airbnb-base

.prettierignore

@@ -1,3 +1,6 @@
 # Handlebars partials are not supported yet
 # @see https://github.com/prettier/prettier/issues/11834
 *.hbs
+
+# Test fixtures are intentionally invalid/non-standard and shouldn't be reformatted
+**/__tests__/__fixtures__/**

eslint.config.js

@@ -6,6 +6,9 @@ import optionalBaseConfig from './packages/eslint-config-base/optional.js';
 import jestConfig from './packages/eslint-config-jest/index.js';
 
 export default [
+  {
+    ignores: ['**/__tests__/__fixtures__/**'],
+  },
   ...baseConfig,
   ...optionalBaseConfig,
   ...jestConfig,

packages/eslint-config-base/__tests__/__fixtures__/invalid.js

@@ -0,0 +1,7 @@
+var mask = 1 & 2;
+
+if (mask == 1) mask = 0;
+
+for (const key in { a: 1 }) {
+  mask += key.length;
+}

packages/eslint-config-base/__tests__/__fixtures__/legacy-valid.js

@@ -0,0 +1,9 @@
+var sum = function sum (a, b) {
+
+  'use strict';
+
+  return a + b;
+
+};
+
+sum(1, 2);

packages/eslint-config-base/__tests__/__fixtures__/valid.js

@@ -0,0 +1,28 @@
+export function sum (a, b) {
+
+  return a + b;
+
+}
+
+export class Counter {
+
+  constructor (start) {
+
+    this.value = start;
+
+  }
+
+  increment () {
+
+    this.value += 1;
+
+    return this.value;
+
+  }
+
+}
+
+const numbers = [1, 2, 3];
+const doubled = numbers.map((number) => number * 2);
+
+export default doubled;

packages/eslint-config-base/__tests__/index.test.js

@@ -0,0 +1,115 @@
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import { describe, it } from 'node:test';
+import { ESLint } from 'eslint';
+import baseConfig from '../index.js';
+import legacyConfig from '../legacy.js';
+import optionalConfig from '../optional.js';
+import whitespaceConfig from '../whitespace.js';
+
+const readFixture = (name) => fs.readFileSync(`./__tests__/__fixtures__/${name}`, 'utf-8');
+
+const lint = async (config, code) => {
+  const eslint = new ESLint({
+    overrideConfigFile: true,
+    overrideConfig: config,
+  });
+
+  const [result] = await eslint.lintText(code, { filePath: 'fixture.js' });
+
+  return result;
+};
+
+describe('@alma-oss/eslint-config-base', () => {
+  describe('flags no problems with valid code', () => {
+    it('has no errors or warnings', async () => {
+      const result = await lint(baseConfig, readFixture('valid.js'));
+
+      assert.equal(result.errorCount, 0);
+      assert.equal(result.warningCount, 0);
+    });
+  });
+
+  describe('flags problems with invalid code', () => {
+    it('flags airbnb rules inherited as-is', async () => {
+      const result = await lint(baseConfig, readFixture('invalid.js'));
+      const ruleIds = result.messages.map((message) => message.ruleId);
+
+      assert.ok(ruleIds.includes('no-var'));
+      assert.ok(ruleIds.includes('eqeqeq'));
+      assert.ok(ruleIds.includes('guard-for-in'));
+    });
+
+    it('flags rules restored during the ESLint v9 style.js migration', async () => {
+      const result = await lint(baseConfig, readFixture('invalid.js'));
+      const noBitwise = result.messages.find((message) => message.ruleId === 'no-bitwise');
+
+      assert.ok(noBitwise, 'expected no-bitwise to be reported');
+      assert.equal(noBitwise.severity, 2);
+    });
+
+    it('respects ALMA severity overrides instead of airbnb defaults', async () => {
+      const result = await lint(baseConfig, readFixture('invalid.js'));
+      const curly = result.messages.find((message) => message.ruleId === 'curly');
+
+      assert.ok(curly, 'expected curly to be reported');
+      assert.equal(curly.severity, 1, 'curly should be a warning, not an airbnb error');
+    });
+
+    it('does not forbid for-in loops, unlike airbnb', async () => {
+      const result = await lint(baseConfig, readFixture('invalid.js'));
+      const ruleIds = result.messages.map((message) => message.ruleId);
+
+      assert.ok(!ruleIds.includes('no-restricted-syntax'));
+    });
+  });
+});
+
+describe('@alma-oss/eslint-config-base/legacy', () => {
+  it('lints ES5 code with no errors or warnings', async () => {
+    const result = await lint(legacyConfig, readFixture('legacy-valid.js'));
+
+    assert.equal(result.errorCount, 0);
+    assert.equal(result.warningCount, 0);
+  });
+
+  it('requires strict mode, unlike the modern config', async () => {
+    const result = await lint(legacyConfig, 'var sum = function sum(a, b) { return a + b; };\n');
+    const ruleIds = result.messages.map((message) => message.ruleId);
+
+    assert.ok(ruleIds.includes('strict'));
+  });
+});
+
+describe('@alma-oss/eslint-config-base/optional', () => {
+  it('loads and lints without throwing', async () => {
+    const result = await lint([...baseConfig, ...optionalConfig], readFixture('valid.js'));
+
+    assert.equal(typeof result.errorCount, 'number');
+  });
+
+  it('flags additional insights not enabled by the base config', async () => {
+    const result = await lint([...baseConfig, ...optionalConfig], 'const foo = Symbol();\n\nexport default foo;\n');
+    const ruleIds = result.messages.map((message) => message.ruleId);
+
+    assert.ok(ruleIds.includes('symbol-description'));
+  });
+});
+
+describe('@alma-oss/eslint-config-base/whitespace', () => {
+  it('keeps whitespace rules at error severity', async () => {
+    const result = await lint(whitespaceConfig, 'if (true) {\n\tconsole.log(1);\n}\n');
+    const indent = result.messages.find((message) => message.ruleId === 'indent');
+
+    assert.ok(indent, 'expected indent to be reported');
+    assert.equal(indent.severity, 2);
+  });
+
+  it('downgrades non-whitespace rules to warnings', async () => {
+    const result = await lint(whitespaceConfig, readFixture('invalid.js'));
+    const noVar = result.messages.find((message) => message.ruleId === 'no-var');
+
+    assert.ok(noVar, 'expected no-var to be reported');
+    assert.equal(noVar.severity, 1, 'no-var is not a whitespace rule, so it should be a warning');
+  });
+});

packages/eslint-config-base/index.js

@@ -1,5 +1,4 @@
-import { FlatCompat } from '@eslint/eslintrc';
-import { fixupConfigRules } from '@eslint/compat';
+import importPlugin from 'eslint-plugin-import';
 import bestPractices from './rules/best-practices.js';
 import errors from './rules/errors.js';
 import node from './rules/node.js';
@@ -11,12 +10,18 @@ import strict from './rules/strict.js';
 import globs from './globs.js';
 import settings from './settings.js';
 
-const compat = new FlatCompat();
-
 export default [
-  ...fixupConfigRules(compat.extends('eslint-config-airbnb-base')),
   {
-    name: '@lmc-eu/eslint-config-base',
+    name: '@alma-oss/eslint-config-base',
+
+    plugins: {
+      import: importPlugin,
+    },
+
+    languageOptions: {
+      ecmaVersion: 2018,
+      sourceType: 'module',
+    },
 
     settings,
 

packages/eslint-config-base/legacy.js

@@ -1,13 +1,78 @@
-import { FlatCompat } from '@eslint/eslintrc';
-import { fixupConfigRules } from '@eslint/compat';
-
-const compat = new FlatCompat();
+import importPlugin from 'eslint-plugin-import';
+import bestPractices from './rules/best-practices.js';
+import errors from './rules/errors.js';
+import node from './rules/node.js';
+import style from './rules/style.js';
+import variables from './rules/variables.js';
+import globs from './globs.js';
+import settings from './settings.js';
 
 export default [
-  ...fixupConfigRules(compat.extends('eslint-config-airbnb-base/legacy')),
   {
-    name: '@lmc-eu/eslint-config-base/legacy',
+    name: '@alma-oss/eslint-config-base/legacy',
+
+    plugins: {
+      import: importPlugin,
+    },
+
+    languageOptions: {
+      ecmaVersion: 5,
+      sourceType: 'script',
+    },
+
+    settings,
 
     rules: {},
   },
+  bestPractices,
+  errors,
+  node,
+  style,
+  variables,
+  {
+    name: '@alma-oss/eslint-config-base/legacy-overrides',
+    rules: {
+      // === AIRBNB LEGACY OVERRIDES ===
+      // Legacy requires never trailing commas
+      'comma-dangle': ['error', 'never'],
+
+      // Prefer numeric literals (off in legacy)
+      'prefer-numeric-literals': 'off',
+
+      // Restrict some object properties
+      'no-restricted-properties': [
+        'error',
+        {
+          object: 'arguments',
+          property: 'callee',
+          message: 'arguments.callee is deprecated',
+        },
+        {
+          property: '__defineGetter__',
+          message: 'Please use Object.defineProperty instead.',
+        },
+        {
+          property: '__defineSetter__',
+          message: 'Please use Object.defineProperty instead.',
+        },
+      ],
+
+      // Allow var in legacy code
+      'no-var': 'off',
+
+      // Allow prefer-object-spread in legacy code
+      'prefer-object-spread': 'off',
+
+      // Require strict mode ('safe' allows function or global)
+      strict: ['error', 'safe'],
+    },
+  },
+  {
+    files: globs.configs,
+
+    rules: {
+      // Using process.env is encouraged in configuration files
+      'node/no-process-env': 'off',
+    },
+  },
 ];

packages/eslint-config-base/optional.js

@@ -4,7 +4,7 @@ import globs from './globs.js';
 export default [
   jsdoc.configs['flat/recommended'],
   {
-    name: '@lmc-eu/eslint-config-base/optional',
+    name: '@alma-oss/eslint-config-base/optional',
     plugins: {
       jsdoc,
     },
@@ -106,10 +106,6 @@ export default [
       // https://eslint.org/docs/rules/strict
       strict: 'error', // airbnb error
 
-      // Require an empty line before return statements
-      // https://eslint.org/docs/rules/newline-before-return
-      'newline-before-return': 'error', // airbnb off
-
       // Disallow duplicate module imports
       // https://eslint.org/docs/rules/no-duplicate-imports
       'no-duplicate-imports': 'error', // airbnb off

packages/eslint-config-base/package.json

@@ -18,6 +18,9 @@
   "engines": {
     "node": ">=20"
   },
+  "scripts": {
+    "test": "node --test"
+  },
   "exports": {
     ".": "./index.js",
     "./optional": "./optional.js",
@@ -34,9 +37,7 @@
     "url": "https://github.com/lmc-eu/code-quality-tools/issues"
   },
   "dependencies": {
-    "@eslint/compat": "^1.3.1",
-    "@eslint/eslintrc": "^3.3.1",
-    "eslint-config-airbnb-base": "^15.0.0",
+    "confusing-browser-globals": "^1.0.10",
     "eslint-plugin-import": "^2.32.0",
     "eslint-plugin-jsdoc": "^51.4.1"
   },