Upgrade ESLint from v8 to v9 (#431)

* build: upgrade `eslint` to 9.16.0

* build: upgrade `eslint-plugin-ember` to 12.3.3

* build: upgrade `eslint-plugin-n` to 17.14.0

* build: upgrade `eslint-plugin-qunit` to 8.1.2

* chore: run `npx @eslint/migrate-config`

Command executed:

```
npx @eslint/migrate-config .eslintrc.js
```

* build: add `globals@15.12.0`

* build: add `@eslint/js@9.16.0`

* build: add `@eslint/eslintrc@3.2.0`

* build: add `typescript-eslint@8.16.0`

https://typescript-eslint.io/packages/typescript-eslint/

* build: deduplicate lockfile

Commands executed:
1. `npx yarn-deduplicate`
2. `yarn`

* refactor: run lint auto-fix

* refactor: rename imported symbols

* chore: delete legacy files from ESLint before v9

* chore: fix relative file paths

Looks like a bug:
eslint/eslint#18757

* chore: add `.mjs` files to Prettier

* refactor: make use of helper `tseslint.config()`

https://typescript-eslint.io/packages/typescript-eslint/#config

* refactor: use flat configs of plugins applied globally

* refactor: merge configs for `eslint-plugin-n`

* refactor: use flat config of `eslint-plugin-n`

* refactor: use flat config of `eslint-plugin-qunit`

* refactor: merge configs for `@typescript-eslint`

* refactor: restore comment for rules `@typescript-eslint`

* refactor: use flat config of `@typescript-eslint`

* refactor: remove unused `FlatCompat`

.npmignore

@@ -7,8 +7,6 @@
 /.ember-cli
 /.env*
 /.eslintcache
-/.eslintignore
-/.eslintrc.js
 /.git/
 /.github/
 /.gitignore

.prettierrc.js

@@ -3,7 +3,7 @@
 module.exports = {
   overrides: [
     {
-      files: '*.{js,ts}',
+      files: '*.{js,mjs,ts}',
       options: {
         semi: false,
         singleQuote: true,

eslint.config.mjs

@@ -0,0 +1,127 @@
+import globals from 'globals'
+import tseslint from 'typescript-eslint'
+
+import pluginEmber from 'eslint-plugin-ember'
+import pluginEmberRecommended from 'eslint-plugin-ember/configs/recommended'
+import pluginEslintJs from '@eslint/js'
+import pluginNode from 'eslint-plugin-n'
+import pluginPrettierRecommended from 'eslint-plugin-prettier/recommended'
+import pluginQunitRecommended from 'eslint-plugin-qunit/configs/recommended'
+
+export default tseslint.config(
+  pluginEslintJs.configs.recommended,
+  // @ts-expect-error: See https://github.com/ember-tooling/ember-eslint-parser/issues/113
+  ...pluginEmberRecommended,
+  pluginPrettierRecommended,
+
+  {
+    ignores: [
+      // Unconventional js
+      'blueprints/*/files/',
+
+      // Compiled output
+      'dist/',
+
+      // Misc
+      'coverage/',
+      '!**/.*',
+      '**/.*/',
+
+      // ember -try
+      '.node_modules.ember-try/',
+      'npm-shrinkwrap.json.ember-try',
+      'package.json.ember-try',
+      'package-lock.json.ember-try',
+      'yarn.lock.ember-try',
+    ],
+  },
+  {
+    plugins: {
+      ember: pluginEmber,
+      '@typescript-eslint': tseslint.plugin,
+    },
+
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+      },
+
+      parser: tseslint.parser,
+      ecmaVersion: 'latest',
+      sourceType: 'script',
+    },
+
+    rules: {
+      '@typescript-eslint/ban-ts-comment': [
+        'error',
+        {
+          'ts-check': 'allow-with-description',
+          'ts-expect-error': 'allow-with-description',
+          'ts-ignore': 'allow-with-description',
+          'ts-nocheck': 'allow-with-description',
+          /**
+           * Count 2 characters for `: ` when giving a description.
+           *
+           * @ts-nocheck: a
+           *            ^^^--- Description of 3 characters
+           *
+           * @ts-nocheck: abc
+           *            ^^^^^--- Description of 5 characters
+           */
+          minimumDescriptionLength: 7, // minimum of 2 + 5
+        },
+      ],
+
+      // This rule is overriden and configured in the `overrides` Array below
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+
+      'no-empty-function': 'off',
+      '@typescript-eslint/no-empty-function': ['error'],
+    },
+  },
+  {
+    // Config for Typescript files
+
+    extends: [tseslint.configs.recommended],
+
+    files: ['**/*.ts'],
+
+    rules: {
+      '@typescript-eslint/explicit-module-boundary-types': ['error'],
+      '@typescript-eslint/no-unused-vars': 'off',
+      'no-undef': 'off',
+      'no-unused-vars': 'off',
+    },
+  },
+  {
+    // Config for Node files
+
+    ...pluginNode.configs['flat/recommended-script'],
+
+    files: [
+      '.prettierrc.js',
+      '.stylelintrc.js',
+      '.template-lintrc.js',
+      'ember-cli-build.js',
+      'eslint.config.mjs',
+      'index.js',
+      'testem.js',
+      'blueprints/*/index.js',
+      'config/**/*.js',
+      'tests/dummy/config/**/*.js',
+    ],
+
+    languageOptions: {
+      globals: {
+        ...Object.fromEntries(Object.entries(globals.browser).map(([key]) => [key, 'off'])),
+        ...globals.node,
+      },
+    },
+  },
+  {
+    // Config for test files
+
+    ...pluginQunitRecommended,
+    files: ['tests/**/*-test.{js,ts}'],
+  },
+)

package.json

@@ -74,6 +74,8 @@
     "@ember/optional-features": "^2.0.0",
     "@ember/test-helpers": "^4.0.2",
     "@embroider/test-setup": "^4.0.0",
+    "@eslint/eslintrc": "^3.2.0",
+    "@eslint/js": "^9.16.0",
     "@glint/environment-ember-loose": "^1.2.1",
     "@glint/template": "^1.2.1",
     "@tsconfig/ember": "^3.0.2",
@@ -100,8 +102,6 @@
     "@types/ember__utils": "^4.0.5",
     "@types/qunit": "^2.19.7",
     "@types/rsvp": "^4.0.6",
-    "@typescript-eslint/eslint-plugin": "^7.0.0",
-    "@typescript-eslint/parser": "^6.9.1",
     "broccoli-asset-rev": "^3.0.0",
     "concurrently": "^9.0.1",
     "ember-auto-import": "^2.6.3",
@@ -116,18 +116,20 @@
     "ember-source": "~5.11.0",
     "ember-source-channel-url": "^3.0.0",
     "ember-try": "^3.0.0",
-    "eslint": "^8.52.0",
+    "eslint": "^9.16.0",
     "eslint-config-prettier": "^9.0.0",
-    "eslint-plugin-ember": "^12.0.0",
-    "eslint-plugin-n": "^17.4.0",
+    "eslint-plugin-ember": "^12.3.3",
+    "eslint-plugin-n": "^17.14.0",
     "eslint-plugin-prettier": "^5.0.1",
-    "eslint-plugin-qunit": "^8.0.1",
+    "eslint-plugin-qunit": "^8.1.2",
+    "globals": "^15.12.0",
     "loader.js": "^4.7.0",
     "prettier": "^3.0.3",
     "qunit": "^2.20.0",
     "qunit-dom": "^3.0.0",
     "rimraf": "^5.0.1",
     "typescript": "^5.2.2",
+    "typescript-eslint": "^8.16.0",
     "webpack": "^5.89.0"
   },
   "peerDependencies": {