From acbd54322f447caaee09b1262e4687434ea0268c Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Wed, 9 Mar 2022 06:49:58 -0600
Subject: [PATCH] Ensure mjs files are transformed with jest (#34698)

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>
---
 packages/next/build/jest/jest.ts            |  2 +-
 packages/next/build/swc/jest-transformer.js |  4 ----
 test/production/next/jest/index.test.ts     | 15 +++++++++++++++
 test/unit/jest-next-swc.test.ts             |  1 -
 4 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/packages/next/build/jest/jest.ts b/packages/next/build/jest/jest.ts
index 45733ea25322..4af9d9afb83a 100644
--- a/packages/next/build/jest/jest.ts
+++ b/packages/next/build/jest/jest.ts
@@ -100,7 +100,7 @@ export default function nextJest(options: { dir?: string } = {}) {
 
         transform: {
           // Use SWC to compile tests
-          '^.+\\.(js|jsx|ts|tsx)$': [
+          '^.+\\.(js|jsx|ts|tsx|mjs)$': [
             require.resolve('../swc/jest-transformer'),
             {
               nextConfig,
diff --git a/packages/next/build/swc/jest-transformer.js b/packages/next/build/swc/jest-transformer.js
index b58b9a102fc7..18c15b6f2a94 100644
--- a/packages/next/build/swc/jest-transformer.js
+++ b/packages/next/build/swc/jest-transformer.js
@@ -37,10 +37,6 @@ const isSupportEsm = 'Module' in vm
 module.exports = {
   createTransformer: (inputOptions) => ({
     process(src, filename, jestOptions) {
-      if (!/\.[jt]sx?$/.test(filename)) {
-        return src
-      }
-
       const jestConfig = getJestConfig(jestOptions)
 
       let swcTransformOpts = getJestSWCOptions({
diff --git a/test/production/next/jest/index.test.ts b/test/production/next/jest/index.test.ts
index 73265c52fcdb..f981254067a4 100644
--- a/test/production/next/jest/index.test.ts
+++ b/test/production/next/jest/index.test.ts
@@ -80,6 +80,21 @@ describe('next/jest', () => {
             });
           });
         `,
+        'lib/hello.mjs': `
+          import path from 'path'
+
+          export default function hello() {
+            return path.join('hello', 'world')
+          }
+        `,
+        'test/mjs-support.test.js': `
+          import path from 'path'
+          import hello from '../lib/hello.mjs'
+          
+          it('should transpile .mjs file correctly', async () => {
+            expect(hello()).toBe(path.join('hello', 'world'))
+          })
+        `,
         'test/mock.test.js': `
           import router from 'next/router'
 
diff --git a/test/unit/jest-next-swc.test.ts b/test/unit/jest-next-swc.test.ts
index 55e10a32998c..a74277e8d815 100644
--- a/test/unit/jest-next-swc.test.ts
+++ b/test/unit/jest-next-swc.test.ts
@@ -1,5 +1,4 @@
 /* eslint-env jest */
-
 describe('jest next-swc preset', () => {
   it('should have correct env', async () => {
     expect(process.env.NODE_ENV).toBe('test')