From dd536a51ecba706cbe4de248d0f68dbcf4f29755 Mon Sep 17 00:00:00 2001
From: Karl Horky <karl.horky@gmail.com>
Date: Mon, 11 Mar 2024 22:19:50 +0100
Subject: [PATCH] Switch to .cjs PostCSS config (#58380)

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### What?

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### What?

Prevent confusing error messages when changing to `"type": "module"` in
`package.json`

```
./node_modules/next/dist/build/webpack/loaders/css-loader/src/index.js??ruleSet[1].rules[2].oneOf[8].use[1]!./node_modules/next/dist/build/webpack/loaders/postcss-loader/src/index.js??ruleSet[1].rules[2].oneOf[8].use[2]!./src/styles/index.css
Error [ERR_REQUIRE_ESM]: require() of ES Module /path/to/my/repo/components/postcss.config.js from /path/to/my/repo/components/node_modules/next/dist/lib/find-config.js not supported.
Instead change the require of postcss.config.js in /path/to/my/repo/components/node_modules/next/dist/lib/find-config.js to a dynamic import() which is available in all CommonJS modules.
```

### Why?

Even though PostCSS itself [supports ESM and TypeScript configuration
files](https://github.com/postcss/postcss-load-config/issues/230),
Next.js itself does not (because of `next/lib/find-config`):

- https://github.com/vercel/next.js/issues/34448

### How?

By switching to `.cjs`, the config will stay recognized as CommonJS even
after switching to `"type": "module"` in `package.json`

cc @balazsorban44

---------

Co-authored-by: Sam Ko <sam@vercel.com>
---
 .../app-tw/js/{postcss.config.js => postcss.config.cjs}   | 0
 .../app-tw/ts/{postcss.config.js => postcss.config.cjs}   | 0
 .../js/{postcss.config.js => postcss.config.cjs}          | 0
 .../ts/{postcss.config.js => postcss.config.cjs}          | 0
 packages/create-next-app/templates/index.ts               | 2 +-
 test/integration/create-next-app/lib/specification.ts     | 8 ++++----
 test/integration/create-next-app/lib/utils.ts             | 2 +-
 7 files changed, 6 insertions(+), 6 deletions(-)
 rename packages/create-next-app/templates/app-tw/js/{postcss.config.js => postcss.config.cjs} (100%)
 rename packages/create-next-app/templates/app-tw/ts/{postcss.config.js => postcss.config.cjs} (100%)
 rename packages/create-next-app/templates/default-tw/js/{postcss.config.js => postcss.config.cjs} (100%)
 rename packages/create-next-app/templates/default-tw/ts/{postcss.config.js => postcss.config.cjs} (100%)

diff --git a/packages/create-next-app/templates/app-tw/js/postcss.config.js b/packages/create-next-app/templates/app-tw/js/postcss.config.cjs
similarity index 100%
rename from packages/create-next-app/templates/app-tw/js/postcss.config.js
rename to packages/create-next-app/templates/app-tw/js/postcss.config.cjs
diff --git a/packages/create-next-app/templates/app-tw/ts/postcss.config.js b/packages/create-next-app/templates/app-tw/ts/postcss.config.cjs
similarity index 100%
rename from packages/create-next-app/templates/app-tw/ts/postcss.config.js
rename to packages/create-next-app/templates/app-tw/ts/postcss.config.cjs
diff --git a/packages/create-next-app/templates/default-tw/js/postcss.config.js b/packages/create-next-app/templates/default-tw/js/postcss.config.cjs
similarity index 100%
rename from packages/create-next-app/templates/default-tw/js/postcss.config.js
rename to packages/create-next-app/templates/default-tw/js/postcss.config.cjs
diff --git a/packages/create-next-app/templates/default-tw/ts/postcss.config.js b/packages/create-next-app/templates/default-tw/ts/postcss.config.cjs
similarity index 100%
rename from packages/create-next-app/templates/default-tw/ts/postcss.config.js
rename to packages/create-next-app/templates/default-tw/ts/postcss.config.cjs
diff --git a/packages/create-next-app/templates/index.ts b/packages/create-next-app/templates/index.ts
index 717d931fa6d5a..170916d8f7608 100644
--- a/packages/create-next-app/templates/index.ts
+++ b/packages/create-next-app/templates/index.ts
@@ -51,7 +51,7 @@ export const installTemplate = async ({
   if (!tailwind)
     copySource.push(
       mode == "ts" ? "tailwind.config.ts" : "!tailwind.config.js",
-      "!postcss.config.js",
+      "!postcss.config.cjs",
     );
 
   await copy(copySource, root, {
diff --git a/test/integration/create-next-app/lib/specification.ts b/test/integration/create-next-app/lib/specification.ts
index c4071032f3f31..7ac5a27c6b996 100644
--- a/test/integration/create-next-app/lib/specification.ts
+++ b/test/integration/create-next-app/lib/specification.ts
@@ -68,7 +68,7 @@ export const projectSpecification: ProjectSpecification = {
         'pages/_app.js',
         'pages/api/hello.js',
         'pages/index.js',
-        'postcss.config.js',
+        'postcss.config.cjs',
         'tailwind.config.js',
       ],
       deps: [],
@@ -80,7 +80,7 @@ export const projectSpecification: ProjectSpecification = {
         'pages/_app.tsx',
         'pages/api/hello.ts',
         'pages/index.tsx',
-        'postcss.config.js',
+        'postcss.config.cjs',
         'tailwind.config.ts',
         'tsconfig.json',
       ],
@@ -125,7 +125,7 @@ export const projectSpecification: ProjectSpecification = {
         'app/layout.js',
         'app/page.js',
         'jsconfig.json',
-        'postcss.config.js',
+        'postcss.config.cjs',
         'tailwind.config.js',
       ],
     },
@@ -143,7 +143,7 @@ export const projectSpecification: ProjectSpecification = {
         'app/layout.tsx',
         'app/page.tsx',
         'next-env.d.ts',
-        'postcss.config.js',
+        'postcss.config.cjs',
         'tailwind.config.ts',
         'tsconfig.json',
       ],
diff --git a/test/integration/create-next-app/lib/utils.ts b/test/integration/create-next-app/lib/utils.ts
index 91495a69f0b26..0c1a9633eac9c 100644
--- a/test/integration/create-next-app/lib/utils.ts
+++ b/test/integration/create-next-app/lib/utils.ts
@@ -135,7 +135,7 @@ export const shouldBeTemplateProject = ({
     files: getProjectSetting({ template, mode, setting: 'files', srcDir }),
   })
 
-  // Tailwind templates share the same files (tailwind.config.js, postcss.config.js)
+  // Tailwind templates share the same files (tailwind.config.js, postcss.config.cjs)
   if (template !== 'app-tw' && template !== 'default-tw') {
     projectFilesShouldNotExist({
       cwd,