Fix Jest config file imports for Jest v30 ESM compatibility

Jest v30 switched to using Node's native ESM loader for config files,
which requires explicit file extensions in imports. This change adds
support for .ts extensions in Jest config file imports while maintaining
proper TypeScript and ESLint integration.

Changes:
- Created tsconfig.jest-config.json: Separate TypeScript config for Jest
  config files that enables allowImportingTsExtensions
- Updated tsconfig.json: Added project reference to tsconfig.jest-config.json
  and excluded jest.config*.ts files to prevent overlap
- Updated jest.config.*.ts: Changed imports to use explicit .ts extensions
  (e.g., import from './jest.config.ts')
- Updated eslint.config.js: Added specific configuration for Jest config
  files to use the correct tsconfig and ignore build artifacts
- Updated .gitignore: Added .tsbuildinfo/ to ignore TypeScript build output

Benefits:
- IDE support: IDEs automatically use the correct tsconfig via project references
- Clean imports: No @ts-ignore hacks needed
- Full type checking: All files properly type-checked
- All test scripts work: test-all, test-mutation, test-private

Technical details:
- Uses TypeScript composite projects with emitDeclarationOnly to satisfy
  both the composite requirement and allowImportingTsExtensions constraint
- Jest config files loaded by Node ESM require .ts extensions
- Test files continue to use traditional imports (handled by ts-jest)

Author: kapral18

.gitignore

@@ -7,3 +7,4 @@
 /.env
 /src/graphql
 /.eslintcache
+/.tsbuildinfo

eslint.config.js

@@ -26,6 +26,7 @@ module.exports = [
       'src/graphql/generated/**',
       'bin/**',
       'coverage/**',
+      '.tsbuildinfo/**',
     ],
   },
 
@@ -57,9 +58,48 @@ module.exports = [
     ...js.configs.recommended,
   },
 
+  // Jest config files - use separate tsconfig that allows .ts extensions
+  {
+    files: ['jest.config*.ts'],
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+      parser: tsparser,
+      parserOptions: {
+        project: './tsconfig.jest-config.json',
+      },
+      globals: nodeGlobals,
+    },
+    plugins: {
+      '@typescript-eslint': tseslint,
+      import: importPlugin,
+    },
+    rules: {
+      ...js.configs.recommended.rules,
+      ...tseslint.configs.recommended.rules,
+      'import/order': [
+        'error',
+        {
+          alphabetize: { order: 'asc' },
+          'newlines-between': 'never',
+          groups: ['builtin', 'external', 'internal', 'parent', 'sibling', 'index'],
+        },
+      ],
+      'import/no-duplicates': 'error',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-unused-vars': 'error',
+      '@typescript-eslint/prefer-nullish-coalescing': 'error',
+      '@typescript-eslint/prefer-optional-chain': 'error',
+      '@typescript-eslint/consistent-type-imports': 'error',
+      '@typescript-eslint/no-floating-promises': 'error',
+      'no-unused-vars': 'off',
+    },
+  },
+
   // TypeScript files
   {
     files: ['**/*.ts'],
+    ignores: ['jest.config*.ts'],
     languageOptions: {
       ecmaVersion: 'latest',
       sourceType: 'module',

jest.config.all.ts

@@ -1,6 +1,7 @@
-import baseConfig from './jest.config';
+import type { Config } from 'jest';
+import baseConfig from './jest.config.ts';
 
-const config = {
+const config: Config = {
   ...baseConfig,
   modulePathIgnorePatterns: [],
 };

jest.config.mutation.ts

@@ -1,6 +1,7 @@
-import baseConfig from './jest.config';
+import type { Config } from 'jest';
+import baseConfig from './jest.config.ts';
 
-const config = {
+const config: Config = {
   ...baseConfig,
 
   // only include "mutation" tests that cannot run on in parallel (like they are on CI) because they mutate shared state

jest.config.private.ts

@@ -1,6 +1,7 @@
-import baseConfig from './jest.config';
+import type { Config } from 'jest';
+import baseConfig from './jest.config.ts';
 
-const config = {
+const config: Config = {
   ...baseConfig,
 
   // only include (private) tests that cannot run on CI because they require credentials and thus exclude external contributors

tsconfig.jest-config.json

@@ -0,0 +1,22 @@
+{
+  "compilerOptions": {
+    "target": "ES2021",
+    "lib": ["ES2021", "DOM"],
+    "module": "CommonJS",
+    "strict": true,
+    "noImplicitAny": true,
+    "strictNullChecks": true,
+    "noImplicitThis": true,
+    "alwaysStrict": true,
+    "noUnusedLocals": true,
+    "esModuleInterop": true,
+    "useUnknownInCatchVariables": true,
+    "resolveJsonModule": true,
+    "forceConsistentCasingInFileNames": true,
+    "allowImportingTsExtensions": true,
+    "emitDeclarationOnly": true,
+    "composite": true,
+    "outDir": "./.tsbuildinfo/jest-config"
+  },
+  "include": ["jest.config*.ts"]
+}

tsconfig.json

@@ -1,17 +1,20 @@
 {
+  "references": [
+    { "path": "./tsconfig.jest-config.json" }
+  ],
   "plugins": [
     {
       "name": "@0no-co/graphqlsp",
       "schema": "./schema.graphql"
     }
   ],
   "include": ["src/**/*"],
-  "exclude": ["src/graphql/generated/graphql.ts"],
+  "exclude": ["src/graphql/generated/graphql.ts", "jest.config*.ts"],
   "compilerOptions": {
     "declaration": true,
     "target": "ES2021",
     "lib": [
-      "ES2021", 
+      "ES2021",
       "DOM" // needed by wonka
     ],
     "module": "CommonJS",
@@ -29,6 +32,6 @@
     "esModuleInterop": true,
     "useUnknownInCatchVariables": true,
     "sourceMap": true,
-    "resolveJsonModule": true,
+    "resolveJsonModule": true
   }
 }