chore: upgrade ESLint to v10 with flat config

Upgrade ESLint from 8.57.0 to 10.5.0. ESLint 10 removes support for the
legacy `.eslintrc` format entirely, so the configuration is migrated to the
new flat config (`eslint.config.mjs`).

Changes:
- Bump `eslint` 8.57.0 -> 10.5.0 and `eslint-plugin-jest` to 29.15.2.
- Replace the legacy `@typescript-eslint/eslint-plugin` + `@typescript-eslint/parser`
  pair with the `typescript-eslint` meta-package (8.62.0), which supports ESLint 10.
- Replace the deprecated `eslint-plugin-node` (unmaintained, broken on ESLint 9+)
  with its maintained fork `eslint-plugin-n` (18.1.0); the single rule in use,
  `node/no-extraneous-import`, becomes `n/no-extraneous-import`.
- Add `@eslint/js` (10.0.1) and `globals` (17.7.0), now required by flat config.
- Translate `.eslintrc.js` to `eslint.config.mjs` and `.eslintignore` to the flat
  config `ignores`, preserving all existing rules and the test-file overrides.
- Update the `lint`/`lint:fix` scripts to invoke `eslint` directly (flat config is
  auto-detected; the `--config ./.eslintrc.js` flag is removed).

`preserve-caught-error` (new in ESLint 10's recommended set) is disabled to keep
the previous lint behavior; adopting it requires an ES2022 target and is left as a
follow-up. Only dev/lint dependencies change, so runtime deps and the built
`dist/` output are unchanged.

Note: `.eslintrc.js` was previously auto-synced from actions/reusable-workflows.
Upstream has not yet published a flat config, so this migration intentionally
deviates from that auto-sync until upstream catches up.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.eslintignore

@@ -1,6 +0,0 @@
-# Ignore list
-/*
-
-# Do not ignore these folders:
-!__tests__/
-!src/

.eslintrc.js

@@ -1,51 +0,0 @@
-// This is a reusable configuration file copied from https://github.com/actions/reusable-workflows/tree/main/reusable-configurations. Please don't make changes to this file as it's the subject of an automatic update.
-module.exports = {
-  extends: [
-    'eslint:recommended',
-    'plugin:@typescript-eslint/recommended',
-    'plugin:eslint-plugin-jest/recommended',
-    'eslint-config-prettier'
-  ],
-  parser: '@typescript-eslint/parser',
-  plugins: ['@typescript-eslint', 'eslint-plugin-node', 'eslint-plugin-jest'],
-  rules: {
-    '@typescript-eslint/no-require-imports': 'error',
-    '@typescript-eslint/no-non-null-assertion': 'off',
-    '@typescript-eslint/no-explicit-any': 'off',
-    '@typescript-eslint/no-empty-function': 'off',
-    '@typescript-eslint/ban-ts-comment': [
-      'error',
-      {
-        'ts-ignore': 'allow-with-description'
-      }
-    ],
-    'no-console': 'error',
-    'yoda': 'error',
-    'prefer-const': [
-      'error',
-      {
-        destructuring: 'all'
-      }
-    ],
-    'no-control-regex': 'off',
-    'no-constant-condition': ['error', {checkLoops: false}],
-    'node/no-extraneous-import': 'error'
-  },
-  overrides: [
-    {
-      files: ['**/*{test,spec}.ts'],
-      rules: {
-        '@typescript-eslint/no-unused-vars': 'off',
-        'jest/no-standalone-expect': 'off',
-        'jest/no-conditional-expect': 'off',
-        'no-console': 'off',
-
-      }
-    }
-  ],
-  env: {
-    node: true,
-    es6: true,
-    'jest/globals': true
-  }
-};

eslint.config.mjs

@@ -0,0 +1,83 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import jestPlugin from 'eslint-plugin-jest';
+import nodePlugin from 'eslint-plugin-n';
+import eslintConfigPrettier from 'eslint-config-prettier';
+import globals from 'globals';
+
+export default tseslint.config(
+  {
+    ignores: [
+      'dist/',
+      'lib/',
+      'node_modules/',
+      'coverage/',
+      '**/*.js',
+      '**/*.cjs',
+      '**/*.mjs',
+      '**/*.d.ts'
+    ]
+  },
+  {
+    files: ['src/**/*.ts', '__tests__/**/*.ts'],
+    extends: [
+      js.configs.recommended,
+      ...tseslint.configs.recommended,
+      jestPlugin.configs['flat/recommended'],
+      eslintConfigPrettier
+    ],
+    plugins: {
+      n: nodePlugin
+    },
+    languageOptions: {
+      ecmaVersion: 2021,
+      sourceType: 'module',
+      globals: {
+        ...globals.node,
+        ...globals.es2021
+      }
+    },
+    rules: {
+      '@typescript-eslint/no-require-imports': 'error',
+      '@typescript-eslint/no-non-null-assertion': 'off',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-empty-function': 'off',
+      '@typescript-eslint/ban-ts-comment': [
+        'error',
+        {
+          'ts-ignore': 'allow-with-description'
+        }
+      ],
+      'no-console': 'error',
+      yoda: 'error',
+      'prefer-const': [
+        'error',
+        {
+          destructuring: 'all'
+        }
+      ],
+      'no-control-regex': 'off',
+      'no-constant-condition': ['error', {checkLoops: false}],
+      // ESLint 10's recommended set adds `preserve-caught-error`, which the
+      // previous ESLint 8 recommended config did not enable. Keep it off to
+      // preserve the prior lint behavior; adopting it would require attaching
+      // an Error `cause` (ES2022) and is out of scope for this upgrade.
+      'preserve-caught-error': 'off',
+      'n/no-extraneous-import': 'error'
+    }
+  },
+  {
+    files: ['**/*{test,spec}.ts'],
+    languageOptions: {
+      globals: {
+        ...globals.jest
+      }
+    },
+    rules: {
+      '@typescript-eslint/no-unused-vars': 'off',
+      'jest/no-standalone-expect': 'off',
+      'jest/no-conditional-expect': 'off',
+      'no-console': 'off'
+    }
+  }
+);

package.json

@@ -11,8 +11,8 @@
     "build": "ncc build -o dist/setup src/setup-java.ts && ncc build -o dist/cleanup src/cleanup-java.ts",
     "format": "prettier --no-error-on-unmatched-pattern --config ./.prettierrc.js --write \"**/*.{ts,yml,yaml}\"",
     "format-check": "prettier --no-error-on-unmatched-pattern --config ./.prettierrc.js --check \"**/*.{ts,yml,yaml}\"",
-    "lint": "eslint --config ./.eslintrc.js \"**/*.ts\"",
-    "lint:fix": "eslint --config ./.eslintrc.js \"**/*.ts\" --fix",
+    "lint": "eslint",
+    "lint:fix": "eslint --fix",
     "prerelease": "npm run-script build",
     "release": "git add -f dist/setup/index.js dist/cleanup/index.js",
     "test": "jest"
@@ -40,21 +40,22 @@
     "xmlbuilder2": "^4.0.3"
   },
   "devDependencies": {
+    "@eslint/js": "^10.0.1",
     "@types/jest": "^30.0.0",
     "@types/node": "^26.0.0",
     "@types/semver": "^7.5.8",
-    "@typescript-eslint/eslint-plugin": "^8.48.0",
-    "@typescript-eslint/parser": "^8.61.1",
     "@vercel/ncc": "^0.44.0",
-    "eslint": "^8.57.0",
+    "eslint": "^10.5.0",
     "eslint-config-prettier": "^10.1.8",
-    "eslint-plugin-jest": "^29.0.1",
-    "eslint-plugin-node": "^11.1.0",
+    "eslint-plugin-jest": "^29.15.2",
+    "eslint-plugin-n": "^18.1.0",
+    "globals": "^17.7.0",
     "jest": "^30.4.2",
     "jest-circus": "^30.4.2",
     "prettier": "^3.6.2",
     "ts-jest": "^29.4.11",
-    "typescript": "^5.3.3"
+    "typescript": "^5.3.3",
+    "typescript-eslint": "^8.62.0"
   },
   "bugs": {
     "url": "https://github.com/actions/setup-java/issues"