Migrate to ESLint flat config

eslint.config.js

@@ -0,0 +1,43 @@
+import zazen from '@zazen/eslint-config'
+import zazenNode from '@zazen/eslint-config/node'
+
+/** @type {import('eslint').Linter.Config[]} */
+const config = [
+	{ ignores: ['**/dist', '**/__tests__/*-errors.js'] },
+	...zazen,
+	...zazenNode,
+	{
+		name: 'project:base',
+		settings: {
+			'import-x/ignore': ['node_modules'],
+			node: {
+				version: '20',
+			},
+		},
+		rules: {
+			// Deprecated rule.
+			'no-return-await': 'off',
+			'import-x/no-anonymous-default-export': [
+				'error',
+				{ allowObject: true },
+			],
+		},
+	},
+	{
+		name: 'project:tests',
+		files: ['**/__tests__/**/*.?(m|c)js'],
+		ignores: ['**/__tests__/*-errors.js'],
+		rules: {
+			'import-x/no-extraneous-dependencies': 'off',
+		},
+	},
+	{
+		name: 'project:configs',
+		files: ['**/eslint.config.js'],
+		rules: {
+			'import-x/no-extraneous-dependencies': 'off',
+		},
+	},
+]
+
+export default config

package.json

@@ -40,7 +40,7 @@
   "devDependencies": {
     "@changesets/cli": "2.27.1",
     "@zazen/eslint-config": "workspace:*",
-    "eslint": "8.56.0",
+    "eslint": "9.0.0",
     "husky": "8.0.3",
     "lint-staged": "15.2.0",
     "prettier": "3.1.1",

packages/eslint-config/README.md

@@ -9,7 +9,7 @@
 
 Install the conventions by running:
 
-```shell
+```sh
 npm install --save-dev eslint @zazen/eslint-config
 ```
 

packages/eslint-config/__tests__/base-errors.js

@@ -0,0 +1,13 @@
+import { bar } from './node-errors'
+import { dirname } from 'node:path'
+
+function q() {
+	const foo = 'FOO'
+	if (foo !== 'FOO') {
+		return bar + dirname(import.meta.url)
+	} else {
+		return foo + bar + dirname(import.meta.url)
+	}
+}
+
+export const foo = 'foo'

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

@@ -0,0 +1,51 @@
+import { readFile } from 'node:fs/promises'
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+import configBase from '../configs/index.js'
+import configNode from '../configs/node.js'
+import { ESLint } from 'eslint'
+import { describe, expect, it } from 'vitest'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+
+const CONFIG_MAP = {
+	base: {
+		config: configBase,
+		errors: ['prefer-let/prefer-let', 'unicorn/prefer-ternary'],
+	},
+	node: {
+		config: configNode,
+		errors: ['n/no-deprecated-api', 'import-x/extensions'],
+	},
+}
+
+function hasRule(errors, ruleId) {
+	return errors.some((error) => error.ruleId === ruleId)
+}
+
+async function runEslint(string, config) {
+	let linter = new ESLint({
+		overrideConfig: config,
+	})
+
+	let [firstResult] = await linter.lintText(string, {
+		filePath: 'test-file.js',
+	})
+
+	return firstResult.messages
+}
+
+describe.each(['base', 'node'])('%s config', (config) => {
+	it('reports expected errors', async () => {
+		let code = await readFile(
+			path.resolve(__dirname, `./${config}-errors.js`),
+			'utf8',
+		)
+		let errors = await runEslint(code, CONFIG_MAP[config].config)
+
+		for (let rule of CONFIG_MAP[config].errors) {
+			expect(hasRule(errors, rule), JSON.stringify(errors)).toBeTruthy()
+		}
+	})
+})

packages/eslint-config/__tests__/node-errors.js

@@ -0,0 +1,7 @@
+import fs from 'fs'
+
+import { foo } from './base-errors'
+
+fs.exists('./foo.js')
+
+export const bar = 'bar'