fix(lint): migrate to eslint v9 + flat config + recommended rules (#867)

* chore(deps): update eslint to v9 and migrate to flat config

* fix(eslint): fixup all errors found by the new set of eslint rules

BREAKING CHANGE: We updated our config to the recommended typescript-eslint typed rules
 so some types have become stricter than they were before.

.github/actions/lint/action.yml

@@ -3,5 +3,5 @@ description: 'Check files respect ESLint & Prettier rules'
 runs:
     using: composite
     steps:
-        - run: npm run prettier:check && npm run eslint:check
+        - run: npm run lint
           shell: bash

.prettierrc.yml

@@ -0,0 +1,4 @@
+printWidth: 120
+tabWidth: 4
+singleQuote: true
+bracketSpacing: false

commitlint.config.js

@@ -0,0 +1,5 @@
+const Configuration = {
+    extends: ['@commitlint/config-conventional'],
+};
+
+export default Configuration;

eslint.config.js

@@ -0,0 +1,52 @@
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import eslintConfigPrettier from 'eslint-config-prettier';
+import eslintPluginJest from 'eslint-plugin-jest';
+import jsdoc from 'eslint-plugin-jsdoc';
+import {dirname} from 'node:path';
+import {fileURLToPath} from 'node:url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+export default tseslint.config(
+    {ignores: ['dist']},
+    {
+        extends: [
+            eslint.configs.recommended,
+            ...tseslint.configs.recommendedTypeChecked,
+            jsdoc.configs['flat/recommended-typescript'],
+            eslintConfigPrettier,
+        ],
+        languageOptions: {
+            parserOptions: {
+                projectService: true,
+                tsconfigRootDir: __dirname,
+            },
+        },
+        rules: {
+            '@typescript-eslint/no-unused-vars': [
+                'error',
+                {
+                    args: 'all',
+                    argsIgnorePattern: '^_',
+                    caughtErrors: 'all',
+                    caughtErrorsIgnorePattern: '^_',
+                    destructuredArrayIgnorePattern: '^_',
+                    varsIgnorePattern: '^_',
+                    ignoreRestSiblings: true,
+                },
+            ],
+            '@typescript-eslint/prefer-promise-reject-errors': 'warn',
+            '@typescript-eslint/only-throw-error': 'warn',
+            '@typescript-eslint/unbound-method': 'warn',
+        },
+    },
+    {
+        files: ['**/*.spec.ts'],
+        extends: [eslintPluginJest.configs['flat/recommended']],
+        rules: {
+            '@typescript-eslint/no-explicit-any': 'warn',
+        },
+    },
+    {files: ['**/*.js', '**/*.mjs'], ...tseslint.configs.disableTypeChecked},
+);

jest.config.js

@@ -0,0 +1,26 @@
+const unmockedDependencies = ['query-string-esm', 'decode-uri-component', 'split-on-first', 'filter-obj'];
+
+// /*
+//  * For a detailed explanation regarding each configuration property, visit:
+//  * https://jestjs.io/docs/configuration
+//  */
+
+export default {
+    extensionsToTreatAsEsm: ['.ts'],
+    preset: 'ts-jest/presets/default-esm',
+    moduleNameMapper: {
+        '^(\\.{1,2}/.*)\\.js$': '$1',
+        '^#query-string': 'query-string-cjs',
+    },
+    transform: {
+        '^.+\\.[tj]s$': ['ts-jest', {tsconfig: '<rootDir>/../tsconfig.test.json', useESM: true}],
+    },
+    clearMocks: true,
+    collectCoverage: true,
+    collectCoverageFrom: ['<rootDir>/**/*.{ts,tsx}'],
+    coverageDirectory: 'coverage',
+    setupFiles: ['../jest.setup.ts'],
+    transformIgnorePatterns: [`node_modules/(?!(${unmockedDependencies.join('|')}))`],
+    rootDir: './src',
+    testEnvironment: 'node',
+};