chore: migrate eslint to flat config (#2212)

Co-authored-by: Artem Zakharchenko <kettanaito@gmail.com>

Author: KaiSpencer

.eslintignore

@@ -0,0 +1,72 @@
+// @ts-check
+
+import eslint from '@eslint/js'
+import tseslint from 'typescript-eslint'
+import eslintConfigPrettier from 'eslint-config-prettier'
+import eslintPluginPrettier from 'eslint-plugin-prettier/recommended'
+
+export default tseslint.config(
+  eslint.configs.recommended,
+  eslintConfigPrettier,
+  ...tseslint.configs.recommended,
+  {
+    languageOptions: {
+      parserOptions: {
+        ecmaVersion: 2020,
+        sourceType: 'module',
+      },
+    },
+    ignores: ['/lib', '/node', '/native', '/config', 'test'],
+    rules: {
+      'no-console': [
+        'error',
+        {
+          allow: ['warn', 'error', 'group', 'groupCollapsed', 'groupEnd'],
+        },
+      ],
+      'no-async-promise-executor': 'off',
+      'require-yield': 'off',
+      'no-empty-pattern': 'off',
+      'no-control-regex': 'off',
+      '@typescript-eslint/prefer-ts-expect-error': 'error',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      '@typescript-eslint/ban-ts-comment': 'off',
+      '@typescript-eslint/no-namespace': [
+        'error',
+        {
+          allowDeclarations: true,
+        },
+      ],
+      '@typescript-eslint/no-var-requires': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          varsIgnorePattern: '^_',
+          argsIgnorePattern: '^_',
+        },
+      ],
+    },
+  },
+  // Unused variables are useful in test files, and type test files
+  {
+    files: [
+      '**/*.test.ts',
+      '**/*.test-d.ts',
+      '**/*.mocks.ts',
+      '**/*.setup.ts',
+      '**/*.config.ts',
+    ],
+    rules: {
+      'no-console': 'off',
+      '@typescript-eslint/no-unused-vars': 'off',
+    },
+  },
+  {
+    files: ['**/*.test-d.ts'],
+    rules: {
+      '@typescript-eslint/no-unused-expressions': 'off',
+    },
+  },
+  eslintPluginPrettier,
+)

.eslintrc.js

@@ -171,7 +171,7 @@
   "scripts": {
     "start": "tsup --watch",
     "clean": "rimraf ./lib",
-    "lint": "eslint \"{cli,src}/**/*.ts\"",
+    "lint": "eslint \"{cli,src,test}/**/*.ts\"",
     "build": "pnpm clean && cross-env NODE_ENV=production tsup && pnpm patch:dts",
     "patch:dts": "node \"./config/scripts/patch-ts.js\"",
     "publint": "publint",
@@ -259,31 +259,35 @@
   "devDependencies": {
     "@commitlint/cli": "^18.4.4",
     "@commitlint/config-conventional": "^18.4.4",
-    "@graphql-typed-document-node/core": "^3.2.0",
+    "@eslint/eslintrc": "^3.3.1",
+    "@eslint/js": "^9.34.0",
     "@fastify/websocket": "^8.3.1",
+    "@graphql-typed-document-node/core": "^3.2.0",
     "@open-draft/test-server": "^0.4.2",
     "@ossjs/release": "^0.8.1",
     "@playwright/test": "^1.48.0",
+    "@swc/core": "^1.13.5",
+    "@types/eslint__js": "^8.42.3",
     "@types/express": "^4.17.21",
     "@types/json-bigint": "^1.0.4",
-    "@types/node": "~18.19.28",
-    "@types/serviceworker": "^0.0.136",
-    "@typescript-eslint/eslint-plugin": "^8.8.1",
-    "@typescript-eslint/parser": "^8.8.1",
-    "@web/dev-server": "^0.4.6",
-    "axios": "^1.7.7",
+    "@types/node": "18.x",
+    "@typescript-eslint/eslint-plugin": "^8.42.0",
+    "@typescript-eslint/parser": "^8.42.0",
+    "@web/dev-server": "^0.1.38",
+    "axios": "^1.6.5",
     "babel-minify": "^0.5.1",
     "commitizen": "^4.3.1",
     "cross-env": "^7.0.3",
     "cross-fetch": "^4.0.0",
     "cz-conventional-changelog": "3.3.0",
     "esbuild": "^0.25.3",
     "esbuild-loader": "^4.2.2",
-    "eslint": "^8.57.0",
-    "eslint-config-prettier": "^9.1.0",
-    "eslint-plugin-prettier": "^5.2.1",
+    "eslint": "^9.34.0",
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-prettier": "^5.5.4",
     "express": "^5.0.0",
     "fastify": "^4.26.0",
+    "fs-extra": "^11.2.0",
     "fs-teardown": "^0.3.0",
     "glob": "^11.0.0",
     "jsdom": "^25.0.1",
@@ -292,13 +296,14 @@
     "lint-staged": "^15.2.10",
     "msw": "workspace:*",
     "page-with": "^0.6.1",
-    "prettier": "^3.4.2",
+    "prettier": "^3.6.2",
     "publint": "^0.3.12",
     "regenerator-runtime": "^0.14.1",
     "rimraf": "^6.0.1",
     "simple-git-hooks": "^2.9.0",
     "tsup": "^8.4.0",
     "typescript": "^5.9.2",
+    "typescript-eslint": "^8.42.0",
     "undici": "^6.20.0",
     "url-loader": "^4.1.1",
     "vitest": "^3.1.4",