infra: migrate to eslint@9

adjust rule tests to new RuleTester behavior
replaced usages of deprecated APIs

.mocharc.js

@@ -19,8 +19,8 @@ function getRequire() {
         'experimental-loader',
     ];
 
-    for (const package of packages) {
-        packagesSet.add(dirname(require.resolve(`@stylable/${package}/package.json`)));
+    for (const packageName of packages) {
+        packagesSet.add(dirname(require.resolve(`@stylable/${packageName}/package.json`)));
     }
 
     // we get this env variable from ./.vscode/launch.json (f5 - Mocha Current)

eslint.config.mjs

@@ -0,0 +1,55 @@
+import pluginJs from '@eslint/js';
+import configPrettier from 'eslint-config-prettier';
+import pluginTypescript from 'typescript-eslint';
+
+for (const config of pluginTypescript.configs.recommendedTypeChecked) {
+  config.files = ['**/*.{ts,tsx,mts,cts}']; // ensure config only targets TypeScript files
+}
+
+/** @type {import('eslint').Linter.Config[]} */
+export default [
+  {
+    ignores: [
+      '**/dist/',
+      '**/esm/',
+      'packages/create-stylable-app/typings/template.d.ts',
+      'packages/language-service/test/fixtures/server-cases/mixins/',
+      'packages/runtime/stylesheet.d.ts',
+    ],
+  },
+  pluginJs.configs.recommended,
+  {
+    rules: {
+      'no-console': 'off',
+      'no-undef': 'off',
+      'no-unused-vars': ['error', { argsIgnorePattern: '^_', varsIgnorePattern: '^_' }],
+    },
+  },
+  ...pluginTypescript.configs.recommendedTypeChecked,
+  { languageOptions: { parserOptions: { projectService: true } } },
+  {
+    files: ['**/*.{ts,tsx,mts,cts}'],
+    rules: {
+      '@typescript-eslint/no-base-to-string': 'off',
+      '@typescript-eslint/no-empty-object-type': 'off',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-require-imports': 'off',
+
+      '@typescript-eslint/no-unsafe-argument': 'off',
+      '@typescript-eslint/no-unsafe-assignment': 'off',
+      '@typescript-eslint/no-unsafe-call': 'off',
+      '@typescript-eslint/no-unsafe-member-access': 'off',
+      '@typescript-eslint/no-unsafe-return': 'off',
+
+      '@typescript-eslint/no-unused-expressions': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
+      ],
+      '@typescript-eslint/restrict-plus-operands': 'off',
+      '@typescript-eslint/restrict-template-expressions': 'off',
+      '@typescript-eslint/unbound-method': 'off',
+    },
+  },
+  configPrettier,
+];