chore: migrate ESLint config to flat config (#5060)

* chore: migrate ESLint config to flat config

* nit: fix job name to be 'lint'

Author: JoshuaKGoldberg

.eslintignore

@@ -0,0 +1,16 @@
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+      - run: npm install --ignore-scripts
+      - run: npm run lint
+
+name: CI
+
+on:
+  pull_request: ~
+  push:
+    branches:
+      - main

.eslintrc.yml

@@ -0,0 +1,155 @@
+"use strict";
+
+const js = require('@eslint/js');
+const globals = require('globals');
+
+const messages = {
+  gh237: 'See https://github.com/mochajs/mocha/issues/237',
+  gh3604: 'See https://github.com/mochajs/mocha/issues/3604'
+};
+
+module.exports = [
+  {
+    ...js.configs.recommended,
+    languageOptions: {
+      ecmaVersion: 2018,
+      globals: {
+        ...globals.browser,
+        ...globals.node
+      },
+      sourceType: 'script'
+    },
+    rules: {
+      'no-var': 'off',
+      strict: ['error', 'global']
+    }
+  },
+  {
+    files: ['docs/js/**/*.js'],
+    languageOptions: {
+      globals: globals.browser
+    }
+  },
+  {
+    files: [
+      '.eleventy.js',
+      '.wallaby.js',
+      'package-scripts.js',
+      'karma.conf.js',
+      'bin/*',
+      'docs/_data/**/*.js',
+      'lib/cli/**/*.js',
+      'lib/nodejs/**/*.js',
+      'scripts/**/*.{js,mjs}',
+      'test/**/*.{js,mjs}',
+      'test/node-unit/**/*.js'
+    ],
+    languageOptions: {
+      globals: globals.node,
+      ecmaVersion: 2020,
+    }
+  },
+  {
+    files: [
+      'lib/nodejs/esm-utils.js',
+      'rollup.config.js',
+      'scripts/*.mjs',
+      'scripts/pick-from-package-json.js'
+    ],
+    languageOptions: {
+      sourceType: 'module'
+    }
+  },
+  {
+    files: ['test/**/*.{js,mjs}'],
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        ...globals.mocha,
+        ...globals.node,
+        expect: 'readonly'
+      }
+    }
+  },
+  {
+    files: ['test/**/*.mjs'],
+    languageOptions: {
+      sourceType: "module"
+    },
+  },
+  {
+    files: ['bin/*', 'lib/**/*.js'],
+    rules: {
+      'no-restricted-globals': [
+        'error',
+        {
+          message: messages.gh237,
+          name: 'setTimeout'
+        },
+        {
+          message: messages.gh237,
+          name: 'clearTimeout'
+        },
+        {
+          message: messages.gh237,
+          name: 'setInterval'
+        },
+        {
+          message: messages.gh237,
+          name: 'clearInterval'
+        },
+        {
+          message: messages.gh237,
+          name: 'setImmediate'
+        },
+        {
+          message: messages.gh237,
+          name: 'clearImmediate'
+        },
+        {
+          message: messages.gh237,
+          name: 'Date'
+        }
+      ],
+      'no-restricted-modules': ['error', 'timers'],
+      "no-restricted-syntax": ['error',
+        // disallow `global.setTimeout()`, `global.setInterval()`, etc.
+        {
+          message: messages.gh237,
+          selector: 'CallExpression[callee.object.name=global][callee.property.name=/(set|clear)(Timeout|Immediate|Interval)/]'
+        },
+        // disallow `new global.Date()`
+        {
+          message: messages.gh237,
+          selector: 'NewExpression[callee.object.name=global][callee.property.name=Date]'
+        },
+        // disallow property access of `global.<timer>.*`
+        {
+          message: messages.gh237,
+          selector: '*[object.object.name=global][object.property.name=/(Date|(set|clear)(Timeout|Immediate|Interval))/]:expression'
+        }
+      ]
+    }
+  },
+  {
+    files: ['lib/reporters/*.js'],
+    rules: {
+      'no-restricted-syntax': ['error',
+        // disallow Reporters using `console.log()`
+        {
+          message: messages.gh3604,
+          selector: 'CallExpression[callee.object.name=console][callee.property.name=log]'
+        }
+      ]
+    }
+  },
+  {
+    ignores: [
+      '**/*.{fixture,min}.{js,mjs}',
+      'coverage/**',
+      'docs/{_dist,_site,api,example}/**',
+      'out/**',
+      'test/integration/fixtures/**',
+    ],
+  }
+];