no need to try require of mts

SimenB · SimenB · commit ce4cd54d3466 · 2026-05-04T08:42:30.000+02:00
diff --git a/e2e/__tests__/readInitialOptions.test.ts b/e2e/__tests__/readInitialOptions.test.ts
@@ -81,6 +81,15 @@ describe('readInitialOptions', () => {
     });
   });
 
+  onNodeVersions('<22.18', () => {
+    test('should fail to read mts-config/jest.config.mts with a clear error', async () => {
+      const rootDir = resolveFixture('mts-config');
+      await expect(
+        proxyReadInitialOptions(undefined, {cwd: rootDir}),
+      ).rejects.toThrow(/jest\.config\.mts requires native TypeScript support/);
+    });
+  });
+
   test('should be able to skip config reading, instead read from cwd', async () => {
     const expectedConfigFile = resolveFixture(
       'json-config',
diff --git a/packages/jest-config/src/__tests__/readConfigFileAndSetRootDir.test.ts b/packages/jest-config/src/__tests__/readConfigFileAndSetRootDir.test.ts
@@ -25,6 +25,37 @@ describe('readConfigFileAndSetRootDir', () => {
 
       expect(config).toEqual({notify: true, rootDir});
     });
+
+    test('throws a clear error when native import fails, without falling back to ts-node', async () => {
+      jest
+        .mocked(requireOrImportModule)
+        .mockRejectedValueOnce(new Error('Unknown file extension ".mts"'));
+
+      const configPath = path.join(
+        path.resolve('some', 'path', 'to'),
+        'jest.config.mts',
+      );
+      await expect(readConfigFileAndSetRootDir(configPath)).rejects.toThrow(
+        /jest\.config\.mts requires native TypeScript support/,
+      );
+      // loadTSConfigFile reads the file for docblock parsing — it must not be called
+      expect(fs.readFileSync).not.toHaveBeenCalled();
+    });
+
+    test('throws a clear error when native import fails with a SyntaxError', async () => {
+      jest
+        .mocked(requireOrImportModule)
+        .mockRejectedValueOnce(new SyntaxError('Unexpected token'));
+
+      const configPath = path.join(
+        path.resolve('some', 'path', 'to'),
+        'jest.config.mts',
+      );
+      await expect(readConfigFileAndSetRootDir(configPath)).rejects.toThrow(
+        /jest\.config\.mts requires native TypeScript support/,
+      );
+      expect(fs.readFileSync).not.toHaveBeenCalled();
+    });
   });
 
   describe('JavaScript file', () => {
diff --git a/packages/jest-config/src/readConfigFileAndSetRootDir.ts b/packages/jest-config/src/readConfigFileAndSetRootDir.ts
@@ -50,7 +50,14 @@ export default async function readConfigFileAndSetRootDir(
           // Try native node TypeScript support first.
           configObject = await requireOrImportModule<any>(configPath);
         } catch (requireOrImportModuleError) {
-          if (!(requireOrImportModuleError instanceof SyntaxError) && !isMTS) {
+          if (isMTS) {
+            // .mts is always ESM and cannot be loaded via require()/ts-node.
+            throw new Error(
+              'jest.config.mts requires native TypeScript support. Ensure you are using Node.js 22.18+ or 23.6+.',
+              {cause: requireOrImportModuleError},
+            );
+          }
+          if (!(requireOrImportModuleError instanceof SyntaxError)) {
             if (!hasTsLoaderExplicitlyConfigured(configPath)) {
               throw requireOrImportModuleError;
             }
@@ -231,6 +238,7 @@ async function registerTsLoader(loader: TsLoaderModule): Promise<TsLoader> {
     ) {
       throw new Error(
         `Jest: '${loader}' is required for the TypeScript configuration files. Make sure it is installed\nError: ${error.message}`,
+        {cause: error},
       );
     }
 
