Upgrade to ESLint 9 and typescript-eslint 8

common/eslint-config.mjs

@@ -0,0 +1,78 @@
+// Copyright (C) 2026 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only
+
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+/**
+ * Shared ESLint configuration for the Qt VS Code extensions.
+ *
+ * `@eslint/js` and `typescript-eslint` are resolved from the monorepo root
+ * node_modules because this module lives in `common/`.
+ *
+ * @param {object} options
+ * @param {string} options.tsconfigRootDir directory containing the
+ *                                         tsconfig.json used for
+ *                                         type-aware linting
+ */
+export function createConfig({ tsconfigRootDir }) {
+  return tseslint.config(
+    {
+      ignores: ['**/out/**', '**/test/**', '**/webview-ui/**']
+    },
+    {
+      files: ['**/*.ts', '**/*.mts', '**/*.cts'],
+      extends: [
+        js.configs.recommended,
+        tseslint.configs.strictTypeChecked,
+        tseslint.configs.stylisticTypeChecked
+      ],
+      languageOptions: {
+        parserOptions: {
+          project: 'tsconfig.json',
+          tsconfigRootDir
+        }
+      },
+      rules: {
+        '@typescript-eslint/promise-function-async': 'error',
+        '@typescript-eslint/no-useless-empty-export': 'error',
+        'default-param-last': 'off',
+        '@typescript-eslint/default-param-last': 'error',
+        'class-methods-use-this': 'off',
+        '@typescript-eslint/class-methods-use-this': 'error',
+        '@typescript-eslint/no-shadow': 'error',
+        '@typescript-eslint/prefer-readonly': 'error',
+        '@typescript-eslint/return-await': 'error',
+        '@typescript-eslint/no-loop-func': 'error',
+        '@typescript-eslint/no-unnecessary-qualifier': 'error',
+        '@typescript-eslint/prefer-find': 'error',
+        '@typescript-eslint/no-require-imports': 'error',
+        '@typescript-eslint/restrict-plus-operands': 'error',
+        '@typescript-eslint/no-unused-vars': [
+          'error',
+          { caughtErrors: 'none' }
+        ],
+        '@typescript-eslint/no-misused-promises': [
+          'error',
+          // Async overrides of void-returning base class methods are the
+          // established pattern for vscode DebugSession request handlers.
+          { checksVoidReturn: { inheritedMethods: false } }
+        ],
+        '@typescript-eslint/prefer-nullish-coalescing': [
+          'error',
+          // `x ? x : y` differs from `x ?? y` for falsy non-nullish values,
+          // so converting ternaries is not behavior preserving.
+          { ignoreTernaryTests: true }
+        ],
+        '@typescript-eslint/switch-exhaustiveness-check': [
+          'error',
+          { considerDefaultExhaustiveForUnions: true }
+        ],
+        // Type parameters that appear only in the return type are used as
+        // intentional cast-style APIs (e.g. CoreAPI.getValue<T>).
+        '@typescript-eslint/no-unnecessary-type-parameters': 'off',
+        curly: 'error'
+      }
+    }
+  );
+}

eslint.config.mjs

@@ -1,37 +1,11 @@
-import typescriptEslint from '@typescript-eslint/eslint-plugin';
-import tsParser from '@typescript-eslint/parser';
+// Copyright (C) 2026 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only
+
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
-import js from '@eslint/js';
-import { FlatCompat } from '@eslint/eslintrc';
-
-const __filename = fileURLToPath(import.meta.url);
-const __dirname = path.dirname(__filename);
-const compat = new FlatCompat({
-  baseDirectory: __dirname,
-  recommendedConfig: js.configs.recommended,
-  allConfig: js.configs.all
-});
 
-export default [
-  {
-    ignores: ['eslint.config.mjs']
-  },
-  ...compat.extends('./common/.eslintrc.cjs'),
-  {
-    plugins: {
-      '@typescript-eslint': typescriptEslint
-    },
+import { createConfig } from './common/eslint-config.mjs';
 
-    languageOptions: {
-      parser: tsParser,
-      ecmaVersion: 5,
-      sourceType: 'script',
-
-      parserOptions: {
-        project: 'tsconfig.json',
-        tsconfigRootDir: __dirname
-      }
-    }
-  }
-];
+export default createConfig({
+  tsconfigRootDir: path.dirname(fileURLToPath(import.meta.url))
+});