Fix adapter outputs for dynamic metadata routes (#91680)

## Summary

This fixes adapter `onBuildComplete` outputs for dynamic metadata
routes.

## Bug

`handleBuildComplete` skipped metadata routes too aggressively via
`isStaticMetadataFile(...)`, so dynamic metadata routes (for example
`robots.txt` / `sitemap.xml` using `connection()`) were omitted from
`outputs.appRoutes`.

## Fix

Only skip metadata routes when they are actually prerendered/static
(present in prerender manifests). Dynamic metadata routes are now
included in adapter `outputs.appRoutes` as expected.

## Tests

Added e2e coverage in `test/e2e/app-dir/adapter-dynamic-metadata`:
- verifies dynamic `robots.txt`, `sitemap.xml`, and `favicon.ico`
functionality
- verifies adapter output classification for non-deploy runs
- skips output-shape verification in deploy mode
- skips the suite in dev mode

Author: ijjk

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

@@ -1070,8 +1070,26 @@ export async function handleBuildComplete({
           }
           const normalizedPage = normalizeAppPath(page)
 
-          // Skip static metadata routes - they will be output as static files
-          if (isStaticMetadataFile(normalizedPage)) {
+          // Skip static metadata routes only when they are prerendered.
+          // Dynamic metadata routes (e.g. robots/sitemap using connection())
+          // should remain app routes in adapter outputs.
+          const isStaticMetadataRoute = isStaticMetadataFile(normalizedPage)
+          const isPrerenderedMetadataRoute =
+            prerenderManifest.routes[normalizedPage] ||
+            prerenderManifest.dynamicRoutes[normalizedPage] ||
+            config.i18n?.locales?.some((locale) => {
+              const localePathname = path.posix.join(
+                '/',
+                locale,
+                normalizedPage.slice(1)
+              )
+              return (
+                prerenderManifest.routes[localePathname] ||
+                prerenderManifest.dynamicRoutes[localePathname]
+              )
+            })
+
+          if (isStaticMetadataRoute && isPrerenderedMetadataRoute) {
             continue
           }
           const pageFile = path.join(appDistDir, `${page}.js`)

test/e2e/app-dir/adapter-dynamic-metadata/adapter-dynamic-metadata.test.ts

@@ -0,0 +1,65 @@
+import type { NextAdapter } from 'next'
+import { nextTestSetup } from 'e2e-utils'
+
+describe('adapter-dynamic-metadata', () => {
+  const { next, isNextDev, isNextDeploy } = nextTestSetup({
+    files: __dirname,
+  })
+
+  if (isNextDev) {
+    it('should skip next dev', () => {})
+    return
+  }
+
+  if (!isNextDeploy) {
+    it('should classify dynamic metadata routes as app routes in adapter outputs', async () => {
+      const { outputs }: Parameters<NextAdapter['onBuildComplete']>[0] =
+        await next.readJSON('build-complete.json')
+
+      const expectedDynamicMetadataRoutes = [
+        '/robots.txt',
+        '/sitemap.xml',
+        '/favicon.ico',
+      ]
+      const staticFilePathnames = outputs.staticFiles.map(
+        (item) => item.pathname
+      )
+      const prerenderPathnames = outputs.prerenders.map((item) => item.pathname)
+      const appRoutePathnames = outputs.appRoutes.map((item) => item.pathname)
+
+      expect(staticFilePathnames).toEqual(
+        expect.not.arrayContaining(expectedDynamicMetadataRoutes)
+      )
+      expect(prerenderPathnames).toEqual(
+        expect.not.arrayContaining(expectedDynamicMetadataRoutes)
+      )
+      expect(appRoutePathnames).toEqual(
+        expect.arrayContaining(expectedDynamicMetadataRoutes)
+      )
+
+      for (const pathname of expectedDynamicMetadataRoutes) {
+        const appRoute = outputs.appRoutes.find(
+          (item) => item.pathname === pathname
+        )
+        expect(appRoute?.runtime).toBe('nodejs')
+      }
+    })
+  }
+
+  it('should serve dynamic metadata routes', async () => {
+    const robots = await next.fetch('/robots.txt')
+    expect(robots.status).toBe(200)
+    expect(robots.headers.get('content-type')).toContain('text/plain')
+    expect(await robots.text()).toContain('User-Agent: *')
+
+    const sitemap = await next.fetch('/sitemap.xml')
+    expect(sitemap.status).toBe(200)
+    expect(sitemap.headers.get('content-type')).toBe('application/xml')
+    expect(await sitemap.text()).toContain('<urlset')
+
+    const favicon = await next.fetch('/favicon.ico')
+    expect(favicon.status).toBe(200)
+    expect(favicon.headers.get('content-type')).toContain('image/x-icon')
+    expect(await favicon.text()).toContain('dynamic favicon')
+  })
+})

test/e2e/app-dir/adapter-dynamic-metadata/app/favicon.ico/route.ts

@@ -0,0 +1,11 @@
+import { connection } from 'next/server'
+
+export async function GET() {
+  await connection()
+
+  return new Response('dynamic favicon', {
+    headers: {
+      'content-type': 'image/x-icon',
+    },
+  })
+}

test/e2e/app-dir/adapter-dynamic-metadata/app/layout.tsx

@@ -0,0 +1,8 @@
+import { ReactNode } from 'react'
+export default function Root({ children }: { children: ReactNode }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}

test/e2e/app-dir/adapter-dynamic-metadata/app/page.tsx

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

test/e2e/app-dir/adapter-dynamic-metadata/app/robots.ts

@@ -0,0 +1,14 @@
+import type { MetadataRoute } from 'next'
+import { connection } from 'next/server'
+
+export default async function robots(): Promise<MetadataRoute.Robots> {
+  await connection()
+
+  return {
+    rules: {
+      userAgent: '*',
+      allow: '/',
+    },
+    sitemap: 'https://example.com/sitemap.xml',
+  }
+}

test/e2e/app-dir/adapter-dynamic-metadata/app/sitemap.ts

@@ -0,0 +1,12 @@
+import type { MetadataRoute } from 'next'
+import { connection } from 'next/server'
+
+export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
+  await connection()
+
+  return [
+    {
+      url: 'https://example.com',
+    },
+  ]
+}

test/e2e/app-dir/adapter-dynamic-metadata/my-adapter.mjs

@@ -0,0 +1,14 @@
+import fs from 'fs'
+
+/** @type {import('next').NextAdapter} */
+const adapter = {
+  name: 'adapter-dynamic-metadata',
+  onBuildComplete: async (ctx) => {
+    await fs.promises.writeFile(
+      'build-complete.json',
+      JSON.stringify(ctx, null, 2)
+    )
+  },
+}
+
+export default adapter

test/e2e/app-dir/adapter-dynamic-metadata/next.config.js

@@ -0,0 +1,10 @@
+/**
+ * @type {import('next').NextConfig}
+ */
+const nextConfig = {}
+
+if (!process.env.NEXT_ADAPTER_PATH) {
+  nextConfig.adapterPath = require.resolve('./my-adapter.mjs')
+}
+
+module.exports = nextConfig