[metadata] remove the default segement check for metadata rendering (#77119)

### What

Remove the default segment checks for metadata rendering. When the
`default.js` is rendered, it should still have the metadata. It was a
condition added due to possible of duplicated metadata, but it's
resolved by other conditions such as only rendering in child slot, and
hoisting metadata into rsc head for navigation.

Author: huozhi

packages/next/src/server/app-render/create-component-tree.tsx

@@ -21,7 +21,6 @@ import type { LoadingModuleData } from '../../shared/lib/app-router-context.shar
 import type { Params } from '../request/params'
 import { workUnitAsyncStorage } from './work-unit-async-storage.external'
 import { OUTLET_BOUNDARY_NAME } from '../../lib/metadata/metadata-constants'
-import { DEFAULT_SEGMENT_KEY } from '../../shared/lib/segment'
 import type { UseCachePageComponentProps } from '../use-cache/use-cache-wrapper'
 
 /**
@@ -394,19 +393,12 @@ async function createComponentTreeInternal({
 
   // Resolve the segment param
   const actualSegment = segmentParam ? segmentParam.treeSegment : segment
-
-  // Only render metadata on the actual SSR'd segment not the `default` segment,
-  // as it's used as a placeholder for navigation.
-  const isNotDefaultSegment = actualSegment !== DEFAULT_SEGMENT_KEY
-
-  const metadata =
-    isNotDefaultSegment && StreamingMetadata ? <StreamingMetadata /> : undefined
+  const metadata = StreamingMetadata ? <StreamingMetadata /> : undefined
 
   // Use the same condition to render metadataOutlet as metadata
-  const metadataOutlet =
-    isNotDefaultSegment && StreamingMetadataOutlet ? (
-      <StreamingMetadataOutlet />
-    ) : undefined
+  const metadataOutlet = StreamingMetadataOutlet ? (
+    <StreamingMetadataOutlet />
+  ) : undefined
 
   const notFoundElement = NotFound ? (
     <>

test/e2e/app-dir/metadata-streaming/app/dynamic-api/page.tsx

@@ -23,7 +23,7 @@ async function SubComponent() {
 
 export async function generateMetadata() {
   await connection()
-  await new Promise((resolve) => setTimeout(resolve, 3000))
+  await new Promise((resolve) => setTimeout(resolve, 800))
   return {
     title: `Dynamic api ${Math.random()}`,
   }

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@bar/default.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'default @bar'
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@bar/layout.tsx

@@ -0,0 +1,8 @@
+export default function Layout({ children }) {
+  return (
+    <div>
+      <h2>@bar Layout</h2>
+      <div id="bar-children">{children}</div>
+    </div>
+  )
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@bar/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'page @bar'
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@bar/test-page/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'test-page @bar'
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@foo/default.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'default @foo'
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@foo/layout.tsx

@@ -0,0 +1,8 @@
+export default function Layout({ children }) {
+  return (
+    <div>
+      <h2>@foo Layout</h2>
+      <div id="foo-children">{children}</div>
+    </div>
+  )
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@foo/no-bar/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'no-bar @foo'
+}

test/e2e/app-dir/metadata-streaming/app/parallel-routes-default/@foo/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'page @foo'
+}