fix unhandled runtime error when notFound() triggered in generateMeta…

…data w/ parallel routes

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

@@ -443,7 +443,10 @@ async function createComponentTreeInternal({
               injectedJS: injectedJSWithCurrentLayout,
               injectedFontPreloadTags: injectedFontPreloadTagsWithCurrentLayout,
               asNotFound,
-              metadataOutlet,
+              // The metadataOutlet is responsible for throwing any errors that were caught during metadata resolution.
+              // We only want to render an outlet once per segment, as otherwise the error will be triggered
+              // multiple times causing an uncaught error.
+              metadataOutlet: isChildrenRouteKey ? metadataOutlet : undefined,
               ctx,
               missingSlots,
             })

test/e2e/app-dir/parallel-route-not-found/app/@bar/not-found-metadata/page-error/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <div>@bar slot</div>
+}

test/e2e/app-dir/parallel-route-not-found/app/@bar/not-found-metadata/slot-error/page.tsx

@@ -0,0 +1,9 @@
+import { notFound } from 'next/navigation'
+
+export function generateMetadata() {
+  notFound()
+}
+
+export default function Page() {
+  return <div>@bar slot</div>
+}

test/e2e/app-dir/parallel-route-not-found/app/@foo/not-found-metadata/page-error/page.tsx

@@ -0,0 +1,9 @@
+export function generateMetadata() {
+  return {
+    title: 'Create Next App',
+  }
+}
+
+export default function Page() {
+  return <div>@foo slot</div>
+}

test/e2e/app-dir/parallel-route-not-found/app/@foo/not-found-metadata/slot-error/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <div>@foo slot</div>
+}

test/e2e/app-dir/parallel-route-not-found/app/not-found-metadata/not-found.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <div>Custom Not Found!</div>
+}

test/e2e/app-dir/parallel-route-not-found/app/not-found-metadata/page-error/page.tsx

@@ -0,0 +1,9 @@
+import { notFound } from 'next/navigation'
+
+export function generateMetadata() {
+  notFound()
+}
+
+export default function Page() {
+  return <h1>Hello from Page</h1>
+}

test/e2e/app-dir/parallel-route-not-found/app/not-found-metadata/slot-error/page.tsx

@@ -0,0 +1,9 @@
+export function generateMetadata() {
+  return {
+    title: 'Create Next App',
+  }
+}
+
+export default function Page() {
+  return <h1>Hello from Page</h1>
+}

test/e2e/app-dir/parallel-route-not-found/parallel-route-not-found.test.ts

@@ -57,6 +57,34 @@ describe('parallel-route-not-found', () => {
     expect(warnings.length).toBe(0)
   })
 
+  it('should handle `notFound()` in generateMetadata on a page that also renders a parallel route', async () => {
+    const browser = await next.browser('/not-found-metadata/page-error')
+
+    // The page's `generateMetadata` function threw a `notFound()` error,
+    // so we should see the not found page.
+    expect(await browser.elementByCss('body').text()).toContain(
+      'Custom Not Found!'
+    )
+
+    // The slots should still render
+    expect(await browser.elementByCss('body').text()).toContain('@bar slot')
+    expect(await browser.elementByCss('body').text()).toContain('@foo slot')
+  })
+
+  it('should handle `notFound()` in a slot', async () => {
+    const browser = await next.browser('/not-found-metadata/slot-error')
+
+    // The page's `generateMetadata` function threw a `notFound()` error,
+    // so we should see the not found page.
+    expect(await browser.elementByCss('body').text()).toContain(
+      'Custom Not Found!'
+    )
+
+    // The slots should still render
+    expect(await browser.elementByCss('body').text()).toContain('@bar slot')
+    expect(await browser.elementByCss('body').text()).toContain('@foo slot')
+  })
+
   if (isNextDev) {
     it('should not log any warnings for a regular not found page', async () => {
       const browser = await next.browser('/this-page-doesnt-exist')