Fix adapter i18n App route handling

packages/next/src/build/adapter/build-complete.ts

@@ -1240,7 +1240,7 @@ export async function handleBuildComplete({
           config.i18n?.locales || []
         ).pathname
         const parentOutput =
-          pageOutputMap[normalizedSrcRoute] || appOutputMap[normalizedSrcRoute]
+          appOutputMap[srcRoute] || pageOutputMap[normalizedSrcRoute]
 
         if (!parentOutput && !allowMissing) {
           console.error({
@@ -2089,6 +2089,7 @@ export async function handleBuildComplete({
     const dynamicRoutes: DynamicRouteItem[] = []
     const dynamicDataRoutes: DynamicRouteItem[] = []
     const dynamicSegmentRoutes: DynamicRouteItem[] = []
+    const appPathnames = new Set(appPageKeys?.map(normalizeAppPath) ?? [])
 
     const getDestinationQuery = (routeKeys: Record<string, string>) => {
       const items = Object.entries(routeKeys ?? {})
@@ -2131,7 +2132,9 @@ export async function handleBuildComplete({
         route.page
       )
 
-      const shouldLocalize = Boolean(config.i18n && !isAPIRoute(route.page))
+      const shouldLocalize = Boolean(
+        config.i18n && !isAPIRoute(route.page) && !appPathnames.has(route.page)
+      )
 
       const routeRegex = getNamedRouteRegex(route.page, {
         prefixRouteKeys: true,

test/e2e/app-dir/i18n-app-pages-domain-routing/i18n-app-pages-domain-routing.test.ts

@@ -1,16 +1,28 @@
 import { nextTestSetup } from 'e2e-utils'
 import { load } from 'cheerio'
 
+const deploymentHost =
+  process.env.NEXT_TEST_DEPLOYMENT_HOST ||
+  (process.env.VERCEL === '1' ? process.env.VERCEL_URL : undefined)
+
 describe('i18n-app-pages-domain-routing', () => {
-  const { next } = nextTestSetup({
+  const { next, isNextDeploy } = nextTestSetup({
     files: __dirname,
-    // Adapter-generated routing metadata is covered separately. This suite
-    // verifies the built-in router and cannot run in deploy mode until the
-    // adapter-specific follow-up is applied.
-    skipDeployment: true,
+    // This layer includes the adapter routing fix, so exercise the shared
+    // regression fixture in deployment mode as well.
+    skipDeployment: false,
   })
 
-  function fetchFromDomain(pathname: string, host = 'nl.example.local') {
+  function fetchFromDomain(
+    pathname: string,
+    host = deploymentHost || 'nl.example.local'
+  ) {
+    if (isNextDeploy) {
+      // The deployed URL already uses the hostname configured through
+      // NEXT_TEST_DEPLOYMENT_HOST or the provider's deployment environment.
+      return next.fetch(pathname)
+    }
+
     return next.fetch(pathname, {
       headers: { host },
     })

test/e2e/app-dir/i18n-app-pages-domain-routing/next.config.js

@@ -1,6 +1,10 @@
 /**
  * @type {import('next').NextConfig}
  */
+const deploymentHost =
+  process.env.NEXT_TEST_DEPLOYMENT_HOST ||
+  (process.env.VERCEL === '1' ? process.env.VERCEL_URL : undefined)
+
 const nextConfig = {
   i18n: {
     locales: ['en-US', 'nl-NL'],
@@ -12,7 +16,7 @@ const nextConfig = {
         defaultLocale: 'en-US',
       },
       {
-        domain: 'nl.example.local',
+        domain: deploymentHost || 'nl.example.local',
         defaultLocale: 'nl-NL',
       },
     ],

test/e2e/app-dir/i18n-app-pages-domain-routing/proxy.ts

@@ -1,10 +1,18 @@
 import { NextRequest, NextResponse } from 'next/server'
 
+const deploymentHost =
+  process.env.NEXT_TEST_DEPLOYMENT_HOST ||
+  (process.env.VERCEL === '1' ? process.env.VERCEL_URL : undefined)
+
 const localeByHost = new Map([
   ['en.example.local', 'en-US'],
   ['nl.example.local', 'nl-NL'],
 ])
 
+if (deploymentHost) {
+  localeByHost.set(deploymentHost, 'nl-NL')
+}
+
 export function proxy(request: NextRequest) {
   const hostname = request.headers.get('host')?.split(':', 1)[0] || ''
   const locale = localeByHost.get(hostname) || 'en-US'

test/production/adapter-config-i18n/adapter-config-i18n.test.ts

@@ -35,6 +35,51 @@ describe('adapter config with i18n routes', () => {
     )
   })
 
+  it('keeps dynamic App routes in the literal namespace', async () => {
+    const { outputs, routing }: Parameters<NextAdapter['onBuildComplete']>[0] =
+      await next.readJSON('build-complete.json')
+
+    const appPageOutput = outputs.appPages.find(
+      (output) => output.pathname === '/[lang]'
+    )
+    const appRouteOutput = outputs.appRoutes.find(
+      (output) => output.pathname === '/[lang]/endpoint'
+    )
+    const appPageRoute = routing.dynamicRoutes.find(
+      (route) => route.source === '/[lang]'
+    )
+    const appRoute = routing.dynamicRoutes.find(
+      (route) => route.source === '/[lang]/endpoint'
+    )
+
+    expect(appPageOutput).toBeDefined()
+    expect(appRouteOutput).toBeDefined()
+
+    expect(appPageRoute).toBeDefined()
+    expect(appPageRoute?.sourceRegex).not.toContain('nextLocale')
+    expect(appPageRoute?.destination).toBe('/[lang]?nxtPlang=$nxtPlang')
+
+    expect(appRoute).toBeDefined()
+    expect(appRoute?.sourceRegex).not.toContain('nextLocale')
+    expect(appRoute?.destination).toBe('/[lang]/endpoint?nxtPlang=$nxtPlang')
+  })
+
+  it('links prerenders with locale-like App segments to their App output', async () => {
+    const { outputs }: Parameters<NextAdapter['onBuildComplete']>[0] =
+      await next.readJSON('build-complete.json')
+
+    const appPageOutput = outputs.appPages.find(
+      (output) => output.pathname === '/fr/static'
+    )
+    const prerenderOutput = outputs.prerenders.find(
+      (output) => output.pathname === '/fr/static'
+    )
+
+    expect(appPageOutput).toBeDefined()
+    expect(prerenderOutput).toBeDefined()
+    expect(prerenderOutput?.parentOutputId).toBe(appPageOutput?.id)
+  })
+
   it('does not emit outputs multiple times for a given pathname', async () => {
     const { outputs }: Parameters<NextAdapter['onBuildComplete']>[0] =
       await next.readJSON('build-complete.json')

test/production/adapter-config-i18n/app/[lang]/endpoint/route.ts

@@ -0,0 +1,6 @@
+export async function GET(
+  _request: Request,
+  { params }: { params: Promise<{ lang: string }> }
+) {
+  return Response.json({ lang: (await params).lang })
+}

test/production/adapter-config-i18n/app/[lang]/page.tsx

@@ -0,0 +1,7 @@
+export default async function Page({
+  params,
+}: {
+  params: Promise<{ lang: string }>
+}) {
+  return <p>App page: {(await params).lang}</p>
+}

test/production/adapter-config-i18n/app/fr/static/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <p>static App page</p>
+}

test/production/adapter-config-i18n/app/layout.tsx

@@ -0,0 +1,11 @@
+export default function RootLayout({
+  children,
+}: {
+  children: React.ReactNode
+}) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}