chore: fix linting

Tried making a few intentional mistakes, and yes, linting was very broken in
.ts and .svelte.

For consistency and picking a good baseline, I started by pulling the package.json
and eslint differences from the AI Lab extension, which included switching to the
newer eslint.config.mjs config instead of .eslint files. Eslint is updated, and
several plugins were added.

Since the rules in ai-lab are stricter than when eslint stopped working here,
this flagged ~160 'new' issues. This would be too much change for a single PR, so I
fixed all the minor/one-off issues here, disabled rules for the top 4, and opened
#1245 to enable them later.

Fixes #1239.

Signed-off-by: Tim deBoer <[email protected]>

eslint.config.mjs

@@ -0,0 +1,257 @@
+/**********************************************************************
+ * Copyright (C) 2025 Red Hat, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ***********************************************************************/
+
+import globals from 'globals';
+import js from '@eslint/js';
+import typescriptLint from 'typescript-eslint';
+import tsParser from '@typescript-eslint/parser';
+import svelteParser from 'svelte-eslint-parser';
+import importPlugin from 'eslint-plugin-import';
+import { fixupConfigRules, fixupPluginRules } from '@eslint/compat';
+import { fileURLToPath } from 'node:url';
+import path from 'node:path';
+import { FlatCompat } from '@eslint/eslintrc';
+import unicorn from 'eslint-plugin-unicorn';
+import noNull from 'eslint-plugin-no-null';
+import sonarjs from 'eslint-plugin-sonarjs';
+import etc from 'eslint-plugin-etc';
+import svelte from 'eslint-plugin-svelte';
+import redundantUndefined from 'eslint-plugin-redundant-undefined';
+import simpleImportSort from 'eslint-plugin-simple-import-sort';
+
+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,
+});
+
+const TYPESCRIPT_PROJECTS = ['packages/*/tsconfig.json', 'tests/*/tsconfig.json'];
+
+export default [
+  {
+    ignores: [
+      '*.config.*js',
+      '**/*.config.*js',
+      '**/dist/**/*',
+      '**/test-resources',
+      '**/__mocks__/',
+      '**/coverage/',
+      'packages/backend/media/**',
+      '**/.svelte-kit/',
+      'scripts/**',
+      '**/src-generated/',
+    ],
+  },
+  js.configs.recommended,
+  ...typescriptLint.configs.recommended,
+  sonarjs.configs.recommended,
+  ...svelte.configs['flat/recommended'],
+  ...fixupConfigRules(
+    compat.extends('plugin:import/recommended', 'plugin:import/typescript', 'plugin:etc/recommended'),
+  ),
+  {
+    plugins: {
+      // compliant v9 plug-ins
+      unicorn,
+      // non-compliant v9 plug-ins
+      etc: fixupPluginRules(etc),
+      import: fixupPluginRules(importPlugin),
+      'no-null': fixupPluginRules(noNull),
+      'redundant-undefined': fixupPluginRules(redundantUndefined),
+      'simple-import-sort': fixupPluginRules(simpleImportSort),
+    },
+    settings: {
+      'import/resolver': {
+        typescript: true,
+        node: true,
+
+        'eslint-import-resolver-custom-alias': {
+          alias: {
+            '/@': './src',
+            '/@gen': './src-generated',
+          },
+
+          extensions: ['.ts'],
+          packages: ['packages/*'],
+        },
+      },
+    },
+  },
+  {
+    linterOptions: {
+      reportUnusedDisableDirectives: 'off',
+    },
+    languageOptions: {
+      globals: {
+        ...globals.node,
+      },
+      // parser: tsParser,
+      sourceType: 'module',
+      parserOptions: {
+        extraFileExtensions: ['.svelte'],
+        warnOnUnsupportedTypeScriptVersion: false,
+        project: TYPESCRIPT_PROJECTS,
+      },
+    },
+  },
+  {
+    rules: {
+      eqeqeq: 'error',
+      'prefer-promise-reject-errors': 'error',
+      semi: ['error', 'always'],
+      'comma-dangle': ['warn', 'always-multiline'],
+
+      quotes: [
+        'error',
+        'single',
+        {
+          allowTemplateLiterals: true,
+        },
+      ],
+
+      '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_', caughtErrors: 'none' }],
+      '@typescript-eslint/no-var-requires': 'off',
+      '@typescript-eslint/consistent-type-imports': 'error',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/await-thenable': 'error',
+      '@typescript-eslint/no-floating-promises': 'off',
+      '@typescript-eslint/no-misused-promises': 'off',
+      '@typescript-eslint/prefer-optional-chain': 'error',
+      '@typescript-eslint/explicit-function-return-type': 'off',
+      '@typescript-eslint/prefer-nullish-coalescing': [
+        'error',
+        {
+          ignoreConditionalTests: true,
+        },
+      ],
+      '@typescript-eslint/no-require-imports': 'off',
+
+      // unicorn custom rules
+      'unicorn/prefer-node-protocol': 'error',
+      'no-null/no-null': 'error',
+      'sonarjs/no-empty-function': 'off',
+      'sonarjs/deprecation': 'off',
+      'sonarjs/todo-tag': 'off',
+      'sonarjs/sonar-no-fallthrough': 'off',
+
+      /**
+       * Having a semicolon helps the optimizer interpret your code correctly.
+       * This avoids rare errors in optimized code.
+       * @see https://twitter.com/alex_kozack/status/1364210394328408066
+       */
+      semi: ['error', 'always'],
+      /**
+       * This will make the history of changes in the hit a little cleaner
+       */
+      'comma-dangle': ['warn', 'always-multiline'],
+      /**
+       * Just for beauty
+       */
+      quotes: ['error', 'single', { allowTemplateLiterals: true }],
+
+      // disabled import/namespace rule as the plug-in is not fully compatible using the compat mode
+      'import/namespace': 'off',
+      'import/no-duplicates': 'error',
+      'import/first': 'error',
+      'import/newline-after-import': 'error',
+      'import/no-extraneous-dependencies': 'error',
+      'import/no-unresolved': 'off',
+      'import/default': 'off',
+      'import/no-named-as-default-member': 'off',
+      'import/no-named-as-default': 'off',
+      'sonarjs/cognitive-complexity': 'off',
+      'sonarjs/no-duplicate-string': 'off',
+      'sonarjs/no-empty-collection': 'off',
+      'sonarjs/no-small-switch': 'off',
+      'sonarjs/no-unused-expressions': 'off',
+      'etc/no-commented-out-code': 'error',
+      'etc/no-deprecated': 'off',
+      'etc/no-commented-out-code': 'off',
+      'redundant-undefined/redundant-undefined': 'error',
+      'import/no-extraneous-dependencies': 'error',
+      'import/no-restricted-paths': [
+        'error',
+        {
+          zones: [
+            {
+              target: './packages/backend/**/*',
+              from: ['./packages/frontend/**/*'],
+            },
+            {
+              target: './packages/frontend/**/*',
+              from: ['./packages/backend/**/*'],
+            },
+          ],
+        },
+      ],
+
+      // disabled as code in this project is not yet compliant:
+      'svelte/valid-compile': 'off',
+      'no-undef': 'off',
+    },
+  },
+
+  {
+    files: ['**/*.svelte'],
+
+    languageOptions: {
+      parser: svelteParser,
+      ecmaVersion: 5,
+      sourceType: 'script',
+      parserOptions: {
+        parser: tsParser,
+      },
+    },
+
+    rules: {
+      eqeqeq: 'off',
+      'etc/no-implicit-any-catch': 'off',
+      'no-inner-declarations': 'off',
+      'sonarjs/code-eval': 'off',
+      'sonarjs/different-types-comparison': 'off',
+      'sonarjs/prefer-nullish-coalescing': 'off',
+      'sonarjs/no-nested-template-literals': 'off',
+      'sonarjs/no-nested-conditional': 'off',
+      '@typescript-eslint/no-unused-vars': 'off',
+      '@typescript-eslint/ban-types': 'off',
+      '@typescript-eslint/no-unused-expressions': 'off',
+    },
+  },
+
+  {
+    files: ['packages/frontend/**'],
+    languageOptions: {
+      globals: {
+        ...Object.fromEntries(Object.entries(globals.node).map(([key]) => [key, 'off'])),
+        ...globals.browser,
+      },
+    },
+  },
+
+  {
+    files: ['packages/shared/**'],
+    languageOptions: {
+      globals: {
+        ...Object.fromEntries(Object.entries(globals.node).map(([key]) => [key, 'off'])),
+        ...Object.fromEntries(Object.entries(globals.browser).map(([key]) => [key, 'off'])),
+      },
+    },
+  },
+];