feat!: support eslint@9 and flat config

package.json

@@ -28,7 +28,6 @@
         "conventional-changelog-cli": "^5.0.0",
         "eslint": "^9.3.0",
         "eslint-config-prettier": "^9.1.0",
-        "eslint-plugin-local-rules": "^2.0.1",
         "eslint-plugin-prettier": "^5.1.3",
         "pkg-pr-new": "^0.0.5",
         "prettier": "^3.2.5",

packages/eslint-remote-tester/eslint-remote-tester.config.cjs → packages/eslint-remote-tester/eslint-remote-tester.config.js

@@ -1,4 +1,7 @@
-module.exports = {
+import js from '@eslint/js';
+
+/** @type {import('./src/config/types').Config} */
+const config = {
     repositories: [
         'AriPerkkio/eslint-remote-tester-integration-test-target',
         'AriPerkkio/aria-live-capture',
@@ -17,20 +20,7 @@ module.exports = {
 
     concurrentTasks: 3,
 
-    eslintrc: {
-        root: true,
-        env: {
-            es6: true,
-        },
-        parserOptions: {
-            ecmaVersion: 2020,
-            sourceType: 'module',
-            ecmaFeatures: {
-                jsx: true,
-            },
-        },
-        extends: ['eslint:recommended'],
-    },
+    eslintConfig: [js.configs.recommended],
 
     cache: true,
 
@@ -61,3 +51,5 @@ module.exports = {
      */
     onComplete: undefined,
 };
+
+export default config;

packages/eslint-remote-tester/package.json

@@ -22,9 +22,8 @@
     "scripts": {
         "prebuild": "rm -rf ./dist",
         "build": "tsc --project tsconfig.prod.json",
-        "start": "node dist --config eslint-remote-tester.config.cjs",
+        "start": "node dist --config eslint-remote-tester.config.js",
         "start:memory-limit-crash": "NODE_OPTIONS=--max_old_space_size=50 node dist",
-        "lint": "eslint . --max-warnings 0 --ext .js,.ts,.tsx && publint",
         "test:integration": "vitest run --config test/integration/vitest.config.integration.ts",
         "test:smoke": "vitest run --config test/smoke/vitest.config.smoke.ts",
         "validate": "pnpm build && pnpm lint && pnpm test && pnpm test:integration"
@@ -45,15 +44,15 @@
         "simple-git": "^3.24.0"
     },
     "devDependencies": {
+        "@eslint/eslintrc": "^3.1.0",
         "@types/babel__code-frame": "^7.0.6",
         "@types/eslint": "^8.56.10",
         "@types/node": "^20.12.12",
         "@types/object-hash": "^3.0.6",
         "@types/react": "^17.0.80",
-        "@typescript-eslint/eslint-plugin": "^7.11.0",
-        "@typescript-eslint/parser": "^7.11.0",
         "conventional-changelog-cli": "^5.0.0",
-        "eslint": "^8.57.0",
+        "eslint": "^9.3.0",
+        "eslint-plugin-local-rules": "^2.0.1",
         "eslint-remote-tester-repositories": "workspace:*",
         "ink-testing-library": "^2.1.0",
         "node-pty": "^1.0.0",
@@ -63,7 +62,7 @@
         "vitest": "^1.6.0"
     },
     "peerDependencies": {
-        "eslint": ">=7",
+        "eslint": ">=9",
         "ts-node": ">=9.0.0"
     },
     "peerDependenciesMeta": {

packages/eslint-remote-tester/src/config/config.ts

@@ -8,7 +8,7 @@ import { loadConfig } from './load.js';
 import { WorkerData } from '../engine/types.js';
 
 const DEFAULT_CONFIGURATION_FILE_NAME = 'eslint-remote-tester.config';
-const DEFAULT_CONFIGURATION_FILE_JS = `${DEFAULT_CONFIGURATION_FILE_NAME}.cjs`;
+const DEFAULT_CONFIGURATION_FILE_JS = `${DEFAULT_CONFIGURATION_FILE_NAME}.js`;
 const DEFAULT_CONFIGURATION_FILE_TS = `${DEFAULT_CONFIGURATION_FILE_NAME}.ts`;
 const CLI_ARGS_CONFIG = ['-c', '--config'];
 
@@ -48,7 +48,7 @@ if (!fs.existsSync(CONFIGURATION_FILE)) {
     process.exit();
 }
 
-const configFileContents = loadConfig(path.resolve(CONFIGURATION_FILE));
+const configFileContents = await loadConfig(path.resolve(CONFIGURATION_FILE));
 const config = getConfigWithDefaults(configFileContents);
 
 export default config;

packages/eslint-remote-tester/src/config/load.ts

@@ -1,5 +1,5 @@
 import { createRequire } from 'node:module';
-import type { Service, RegisterOptions } from 'ts-node';
+import type { Service } from 'ts-node';
 
 let registerer: Service | null = null;
 const require = createRequire(import.meta.url);
@@ -11,9 +11,7 @@ const interopRequireDefault = (obj: any): { default: any } =>
 /** @internal */
 export const loadTSConfig = (configPath: string) => {
     try {
-        registerer ||= require('ts-node').register({
-            moduleTypes: { '**/*.ts': 'cjs' },
-        } satisfies RegisterOptions) as Service;
+        registerer ||= require('ts-node').register() as Service;
     } catch (e: any) {
         if (e.code === 'MODULE_NOT_FOUND') {
             throw new Error(
@@ -33,10 +31,11 @@ export const loadTSConfig = (configPath: string) => {
     return configObject;
 };
 
-export const loadConfig = (configPath: string) => {
+export const loadConfig = async (configPath: string) => {
     if (configPath.endsWith('.ts')) {
         return loadTSConfig(configPath);
     }
 
-    return require(configPath);
+    const { default: config } = await import(configPath);
+    return config;
 };

packages/eslint-remote-tester/src/config/types.ts

@@ -45,12 +45,12 @@ export interface Config {
      * Supports lazy initialization based on currently tested repository when a function is passed.
      * Function is called with current repository and its location on filesystem.
      */
-    eslintrc:
-        | Linter.Config
+    eslintConfig:
+        | Linter.FlatConfig
         | ((options?: {
               repository: string;
               location: string;
-          }) => Linter.Config);
+          }) => Linter.FlatConfig | Promise<Linter.FlatConfig>);
 
     /** Flag used to set CI mode. `process.env.CI` is used when not set. */
     CI: boolean;
@@ -102,7 +102,10 @@ export interface Config {
     ) => Promise<void> | void;
 }
 
-type RequiredFields = Pick<Config, 'repositories' | 'extensions' | 'eslintrc'>;
+type RequiredFields = Pick<
+    Config,
+    'repositories' | 'extensions' | 'eslintConfig'
+>;
 type OptionalFields = AllKeysOptional<
     Pick<
         Config,

packages/eslint-remote-tester/src/config/validator.ts

@@ -100,7 +100,7 @@ export default async function validate(
         rulesUnderTesting,
         resultParser,
         concurrentTasks,
-        eslintrc,
+        eslintConfig,
         CI,
         logLevel,
         slowLintTimeLimit,
@@ -127,32 +127,34 @@ export default async function validate(
 
     errors.push(validateStringArray('extensions', extensions));
 
-    if (!eslintrc) {
-        errors.push(`Missing eslintrc.`);
+    if (!eslintConfig) {
+        errors.push(`Missing eslintConfig.`);
     } else {
         try {
-            // This will throw when eslintrc is invalid
+            // This will throw when eslintConfig is invalid
             const linter = new ESLint({
-                useEslintrc: false,
+                // @ts-expect-error -- `@types/eslint` for v9 are unavailable
                 overrideConfig:
-                    typeof eslintrc === 'function' ? eslintrc() : eslintrc,
+                    typeof eslintConfig === 'function'
+                        ? await eslintConfig()
+                        : eslintConfig,
             });
 
             errors.push(await validateEslintRules(linter));
         } catch (e) {
-            errors.push(`eslintrc: ${e.message}`);
+            errors.push(`eslintConfig: ${e.message}`);
 
-            if (typeof eslintrc === 'function') {
+            if (typeof eslintConfig === 'function') {
                 errors.push(
-                    'Note that "config.eslintrc" is called with empty options during configuration validation.'
+                    'Note that "config.eslintConfig" is called with empty options during configuration validation.'
                 );
             }
         }
     }
 
     // Optional fields
 
-    // TODO nice-to-have: Validate rules match eslintrc config
+    // TODO nice-to-have: Validate rules match eslintConfig config
     // https://eslint.org/docs/developer-guide/nodejs-api#lintergetrules
     if (rulesUnderTesting) {
         if (Array.isArray(rulesUnderTesting)) {
@@ -294,7 +296,7 @@ export function getConfigWithDefaults(config: ConfigWithOptionals): Config {
 }
 
 /**
- * Validate given rules of `config.eslintrc.rules`
+ * Validate given rules of `config.eslintConfig.rules`
  * - When unknown rules are defined, or known ones are misspelled they are not
  *   reported during linting. We need to specifically look for them.
  */
@@ -313,7 +315,7 @@ async function validateEslintRules(
     }
 
     if (errors.length) {
-        return `Configuration validation errors at eslintrc.rules: \n  - ${errors.join(
+        return `Configuration validation errors at eslintConfig.rules: \n  - ${errors.join(
             '\n  - '
         )}`;
     }

packages/eslint-remote-tester/src/engine/worker-task.ts

@@ -211,25 +211,29 @@ export default async function workerTask(): Promise<void> {
         onReadFailure: () => postMessage({ type: 'READ_FAILURE' }),
     });
 
-    const eslintrc =
-        typeof config.eslintrc === 'function'
-            ? config.eslintrc({
+    const eslintConfig =
+        typeof config.eslintConfig === 'function'
+            ? await config.eslintConfig({
                   repository,
                   location: resolve(`${CACHE_LOCATION}/${repository}`),
               })
-            : config.eslintrc;
+            : config.eslintConfig;
 
     const linter = new ESLint({
-        useEslintrc: false,
-        overrideConfig: eslintrc,
+        // @ts-expect-error -- `@types/eslint` for v9 are unavailable
+        overrideConfigFile: true,
+
+        // @ts-expect-error -- `@types/eslint` for v9 are unavailable
+        overrideConfig: eslintConfig,
 
         // Only rules set in configuration are expected.
         // Ignore all inline configurations found from target repositories.
         allowInlineConfig: false,
 
         // Lint all given files, ignore none. Cache is located under node_modules.
         // config.pathIgnorePattern is used for exclusions.
-        ignore: false,
+        ignore: true,
+        ignorePatterns: ['!**/node_modules/'],
     });
 
     postMessage({ type: 'LINT_START', payload: files.length });

packages/eslint-remote-tester/test/integration/base.config.js

@@ -0,0 +1,26 @@
+/** @type {import('../../src/config/types').Config} */
+const config = {
+    repositories: ['AriPerkkio/eslint-remote-tester-integration-test-target'],
+    extensions: ['.js'],
+    pathIgnorePattern: '(expected-to-be-excluded)',
+    rulesUnderTesting: [
+        'no-unreachable',
+        'no-undef',
+        'no-empty',
+        'getter-return',
+        'no-compare-neg-zero',
+    ],
+    eslintConfig: async function initialize() {
+        const { default: js } = await eval(`import('@eslint/js')`);
+        const { FlatCompat } = await eval(`import('@eslint/eslintrc')`);
+        const compat = new FlatCompat({ baseDirectory: process.cwd() });
+
+        return [
+            js.configs.recommended,
+            ...compat.plugins('eslint-plugin-local-rules'),
+            { rules: { 'local-rules/some-unstable-rule': 'error' } },
+        ];
+    },
+};
+
+export default config;

packages/eslint-remote-tester/test/integration/integration.test.ts

@@ -13,7 +13,7 @@ import { Config } from '../../src/config/types';
 
 const DEBUG_LOG_PATTERN = /\[DEBUG (\S|:)*\] /g;
 
-test('results are rendered on CI mode', async () => {
+test.only('results are rendered on CI mode', async () => {
     const { output } = await runProductionBuild({ CI: true });
     const finalLog = output.pop();
 
@@ -35,16 +35,16 @@ test('results are rendered on CI mode', async () => {
       TypeError: Cannot read property 'someAttribute' of undefined
       Occurred while linting <removed>/node_modules/.cache-eslint-remote-tester/AriPerkkio/eslint-remote-tester-integration-test-target/expected-to-crash-linter.js
       Rule: "local-rules/some-unstable-rule"
-          at Identifier (<removed>/eslint-local-rules.js)
+          at Identifier (<removed>/eslint-local-rules.cjs:22:56)
           at ruleErrorHandler (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/linter.js)
           at <removed>/<package-manager-path>/node_modules/eslint/lib/linter/safe-emitter.js
           at Array.forEach (<anonymous>)
           at Object.emit (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/safe-emitter.js)
           at NodeEventGenerator.applySelector (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/node-event-generator.js)
           at NodeEventGenerator.applySelectors (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/node-event-generator.js)
           at NodeEventGenerator.enterNode (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/node-event-generator.js)
-          at CodePathAnalyzer.enterNode (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/code-path-analysis/code-path-analyzer.js)
-          at <removed>/<package-manager-path>/node_modules/eslint/lib/linter/linter.js
+          at runRules (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/linter.js)
+          at Linter._verifyWithFlatConfigArrayAndWithoutProcessors (<removed>/<package-manager-path>/node_modules/eslint/lib/linter/linter.js)
 
       Repository: AriPerkkio/eslint-remote-tester-integration-test-target
       Rule: no-undef

packages/eslint-remote-tester/test/smoke/base.config.js

@@ -0,0 +1,20 @@
+/** @type {import('../../src/config/types').Config} */
+const config = {
+    repositories: ['AriPerkkio/eslint-remote-tester-integration-test-target'],
+    extensions: ['.js'],
+    rulesUnderTesting: [
+        'local-rules/verbose-rule',
+        'local-rules/verbose-rule-2',
+    ],
+    eslintConfig: async function initialize() {
+        const { FlatCompat } = await eval(`import('@eslint/eslintrc')`);
+        const compat = new FlatCompat({ baseDirectory: process.cwd() });
+
+        return [
+            ...compat.plugins('eslint-plugin-local-rules'),
+            { rules: { 'local-rules/verbose-rule': 'error' } },
+        ];
+    },
+};
+
+export default config;