Remove experimental config from create-next-app (#49241)

## What?

Removes `experimental.appDir` this was leftover from when I flipped the
switch.

Kept the config file as in the future we might add future flags and
such. It also helps that it has the types comment included so you always
get types.

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---------

Co-authored-by: JJ Kasper <jj@jjsweb.site>

Author: timneutkens

packages/create-next-app/templates/app-tw/js/next.config.js

@@ -1,8 +1,4 @@
 /** @type {import('next').NextConfig} */
-const nextConfig = {
-  experimental: {
-    appDir: true,
-  },
-}
+const nextConfig = {}
 
 module.exports = nextConfig

packages/create-next-app/templates/app-tw/ts/next.config.js

@@ -1,8 +1,4 @@
 /** @type {import('next').NextConfig} */
-const nextConfig = {
-  experimental: {
-    appDir: true,
-  },
-}
+const nextConfig = {}
 
 module.exports = nextConfig

packages/create-next-app/templates/app/js/next.config.js

@@ -1,8 +1,4 @@
 /** @type {import('next').NextConfig} */
-const nextConfig = {
-  experimental: {
-    appDir: true,
-  },
-}
+const nextConfig = {}
 
 module.exports = nextConfig

packages/create-next-app/templates/app/ts/next.config.js

@@ -1,8 +1,4 @@
 /** @type {import('next').NextConfig} */
-const nextConfig = {
-  experimental: {
-    appDir: true,
-  },
-}
+const nextConfig = {}
 
 module.exports = nextConfig

packages/next/src/cli/next-dev.ts

@@ -8,7 +8,11 @@ import isError from '../lib/is-error'
 import { getProjectDir } from '../lib/get-project-dir'
 import { CONFIG_FILES, PHASE_DEVELOPMENT_SERVER } from '../shared/lib/constants'
 import path from 'path'
-import type { NextConfig, NextConfigComplete } from '../server/config-shared'
+import {
+  defaultConfig,
+  NextConfig,
+  NextConfigComplete,
+} from '../server/config-shared'
 import { traceGlobals } from '../trace/shared'
 import { Telemetry } from '../telemetry/storage'
 import loadConfig from '../server/config'
@@ -239,7 +243,9 @@ const nextDev: CliCommand = async (argv) => {
     const distDir = path.join(dir, rawNextConfig.distDir || '.next')
     const { pagesDir, appDir } = findPagesDir(
       dir,
-      !!rawNextConfig.experimental?.appDir
+      typeof rawNextConfig?.experimental?.appDir === 'undefined'
+        ? !!defaultConfig.experimental?.appDir
+        : !!rawNextConfig.experimental?.appDir
     )
     const telemetry = new Telemetry({
       distDir,

packages/next/src/lib/turbopack-warning.ts

@@ -120,7 +120,7 @@ export async function validateTurboNextConfig({
       let keys: string[] = []
 
       for (const key in obj) {
-        if (typeof obj[key] === 'undefined') {
+        if (typeof obj?.[key] === 'undefined') {
           continue
         }
 
@@ -145,9 +145,9 @@ export async function validateTurboNextConfig({
         keys = keys.split('.')
       }
       if (keys.length === 1) {
-        return obj[keys[0]]
+        return obj?.[keys?.[0]]
       }
-      return getDeepValue(obj[keys[0]], keys.slice(1))
+      return getDeepValue(obj?.[keys?.[0]], keys.slice(1))
     }
 
     const customKeys = flattenKeys(rawNextConfig)

packages/next/src/server/config.ts

@@ -135,17 +135,6 @@ function assignDefaults(
           for (const featureName of Object.keys(
             value
           ) as (keyof ExperimentalConfig)[]) {
-            const featureValue = value[featureName]
-            if (featureName === 'appDir' && featureValue === true) {
-              // auto enable clientRouterFilter if not manually set
-              // when appDir is enabled
-              if (
-                typeof userConfig.experimental.clientRouterFilter ===
-                'undefined'
-              ) {
-                userConfig.experimental.clientRouterFilter = true
-              }
-            }
             if (
               value[featureName] !== defaultConfig.experimental[featureName]
             ) {
@@ -456,6 +445,13 @@ function assignDefaults(
     silent
   )
 
+  if (
+    typeof userConfig.experimental?.clientRouterFilter === 'undefined' &&
+    result.experimental?.appDir
+  ) {
+    result.experimental.clientRouterFilter = true
+  }
+
   if (
     result.experimental?.outputFileTracingRoot &&
     !isAbsolute(result.experimental.outputFileTracingRoot)

test/.stats-app/next.config.js

@@ -1,8 +1,4 @@
-module.exports = {
-  experimental: {
-    appDir: true,
-  },
-}
+module.exports = {}
 
 // For development: analyze the bundled chunks for stats app
 if (process.env.ANALYZE) {

test/development/acceptance-app/fixtures/app-hmr-changes/next.config.js

@@ -3,7 +3,6 @@ const withMDX = require('@next/mdx')()
 module.exports = withMDX({
   pageExtensions: ['ts', 'tsx', 'js', 'jsx', 'md', 'mdx'],
   experimental: {
-    appDir: true,
     mdxRs: true,
   },
   images: {

test/development/acceptance-app/fixtures/default-template/next.config.js

@@ -1,5 +1 @@
-module.exports = {
-  experimental: {
-    appDir: true,
-  },
-}
+module.exports = {}