Upgrade to ESLint v9 flat config (#34324)

Co-authored-by: Nick Schonning <nschonni@gmail.com>

streaming/.eslintrc.cjs

@@ -1,43 +0,0 @@
-/* eslint-disable import/no-commonjs */
-
-// @ts-check
-
-// @ts-ignore - This needs to be a CJS file (eslint does not yet support ESM configs), and TS is complaining we use require
-const { defineConfig } = require('eslint-define-config');
-
-module.exports = defineConfig({
-  extends: ['../.eslintrc.js'],
-  env: {
-    browser: false,
-  },
-  parserOptions: {
-    project: true,
-    tsconfigRootDir: __dirname,
-    ecmaFeatures: {
-      jsx: false,
-    },
-    ecmaVersion: 2021,
-  },
-  rules: {
-    // In the streaming server we need to delete some variables to ensure
-    // garbage collection takes place on the values referenced by those objects;
-    // The alternative is to declare the variable as nullable, but then we need
-    // to assert it's in existence before every use, which becomes much harder
-    // to maintain.
-    'no-delete-var': 'off',
-
-    // This overrides the base configuration for this rule to pick up
-    // dependencies for the streaming server from the correct package.json file.
-    'import/no-extraneous-dependencies': [
-      'error',
-      {
-        devDependencies: ['streaming/.eslintrc.cjs'],
-        optionalDependencies: false,
-        peerDependencies: false,
-        includeTypes: true,
-        packageDir: __dirname,
-      },
-    ],
-    'import/extensions': ['error', 'always'],
-  },
-});

streaming/eslint.config.mjs

@@ -0,0 +1,45 @@
+// @ts-check
+
+import globals from 'globals';
+import tseslint from 'typescript-eslint';
+
+// eslint-disable-next-line import/no-relative-packages -- Must import from the root
+import { baseConfig } from '../eslint.config.mjs';
+
+export default tseslint.config([
+  baseConfig,
+  {
+    languageOptions: {
+      globals: globals.node,
+
+      parser: tseslint.parser,
+      ecmaVersion: 2021,
+      sourceType: 'module',
+    },
+
+    settings: {
+      'import/ignore': ['node_modules', '\\.(json)$'],
+      'import/resolver': {
+        typescript: {},
+      },
+    },
+
+    rules: {
+      // In the streaming server we need to delete some variables to ensure
+      // garbage collection takes place on the values referenced by those objects;
+      // The alternative is to declare the variable as nullable, but then we need
+      // to assert it's in existence before every use, which becomes much harder
+      // to maintain.
+      'no-delete-var': 'off',
+
+      'import/no-extraneous-dependencies': [
+        'error',
+        {
+          devDependencies: ['**/*.config.mjs'],
+        },
+      ],
+
+      'import/extensions': ['error', 'always'],
+    },
+  },
+]);

streaming/lint-staged.config.mjs

@@ -0,0 +1,7 @@
+const config = {
+  '*': 'prettier --ignore-unknown --write',
+  '*.{js,ts}': 'eslint --fix',
+  '**/*.ts': () => 'tsc -p tsconfig.json --noEmit',
+};
+
+export default config;

streaming/package.json

@@ -31,14 +31,16 @@
     "ws": "^8.12.1"
   },
   "devDependencies": {
+    "@eslint/js": "^9.23.0",
     "@types/cors": "^2.8.16",
     "@types/express": "^4.17.17",
     "@types/pg": "^8.6.6",
     "@types/uuid": "^10.0.0",
     "@types/ws": "^8.5.9",
-    "eslint-define-config": "^2.0.0",
+    "globals": "^16.0.0",
     "pino-pretty": "^13.0.0",
-    "typescript": "^5.0.4"
+    "typescript": "^5.0.4",
+    "typescript-eslint": "^8.28.0"
   },
   "optionalDependencies": {
     "bufferutil": "^4.0.7",

streaming/tsconfig.json

@@ -8,5 +8,5 @@
     "tsBuildInfoFile": "../tmp/cache/streaming/tsconfig.tsbuildinfo",
     "paths": {}
   },
-  "include": ["./*.js", "./.eslintrc.cjs"]
+  "include": ["./*.js"]
 }