Fix missing .rsc outputs for pages prerenders (#11503)

When generating the outputs for pages when app router is also present we weren't creating the placeholder `.rsc` outputs for all prerender outputs so when a `fallback: false` route was configured in the pages router that could fall through to an app route it causes issues with client-navigation behaving differently than a direct visit. 

This ensures we add the placeholder `.rsc` outputs for all prerenders so that `fallback: false` pages don't have this unexpected behavior.

.changeset/clean-buttons-hunt.md

@@ -0,0 +1,5 @@
+---
+"@vercel/next": patch
+---
+
+Fix missing .rsc outputs for pages prerenders

packages/next/src/utils.ts

@@ -2477,6 +2477,22 @@ export const onPrerenderRoute =
         });
       }
 
+      // we need to ensure all prerenders have a matching .rsc output
+      // otherwise routing could fall through unexpectedly for the
+      // fallback: false case as it doesn't have a dynamic route
+      // to catch the `.rsc` request for app -> pages routing
+      if (outputPrerenderPathData?.endsWith('.json') && appDir) {
+        const dummyOutput = new FileBlob({
+          data: '{}',
+          contentType: 'application/json',
+        });
+        const rscKey = `${outputPathPage}.rsc`;
+        const prefetchRscKey = `${outputPathPage}${RSC_PREFETCH_SUFFIX}`;
+
+        prerenders[rscKey] = dummyOutput;
+        prerenders[prefetchRscKey] = dummyOutput;
+      }
+
       ++prerenderGroup;
 
       if (routesManifest?.i18n && isBlocking) {

packages/next/test/fixtures/00-app-dir-no-ppr/app/nested/[...rest]/page.js

@@ -0,0 +1,5 @@
+export default function Page() {
+  return (
+    <p>nested app router catch-all</p>
+  )
+}

packages/next/test/fixtures/00-app-dir-no-ppr/pages/nested/blog-fallback-false/[slug].js

@@ -0,0 +1,24 @@
+export default function Page(props) {
+  return (
+    <>
+      <p>hello from /nested/blog-fallback-false/[slug]</p>
+    </>
+  );
+}
+
+export function getStaticProps() {
+  return {
+    props: {
+      now: Date.now()
+    }
+  }
+}
+
+export function getStaticPaths() {
+  return {
+    paths: [
+      { params: { slug: 'first' } },
+    ],
+    fallback: false
+  }
+}

packages/next/test/fixtures/00-app-dir-no-ppr/vercel.json

@@ -18,6 +18,50 @@
     }
   ],
   "probes": [
+    {
+      "path": "/nested/blog-fallback-false/first",
+      "status": 200,
+      "mustContain": "hello from /nested/blog-fallback-false"
+    },
+    {
+      "path": "/nested/blog-fallback-false/first",
+      "status": 200,
+      "mustContain": "{}",
+      "mustNotContain": ":",
+      "responseHeaders": {
+        "x-matched-path": "/nested/blog-fallback-false/first.prefetch.rsc"
+      },
+      "headers": {
+        "RSC": 1,
+        "Next-Router-Prefetch": 1
+      }
+    },
+    {
+      "path": "/nested/blog-fallback-false/first",
+      "status": 200,
+      "mustContain": "{}",
+      "mustNotContain": ":",
+      "responseHeaders": {
+        "x-matched-path": "/nested/blog-fallback-false/first.rsc"
+      },
+      "headers": {
+        "RSC": 1
+      }
+    },
+    {
+      "path": "/nested/blog-fallback-false/non-existent",
+      "status": 200,
+      "mustContain": "nested app router catch-all"
+    },
+    {
+      "path": "/nested/blog-fallback-false/non-existent",
+      "status": 200,
+      "mustContain": ":",
+      "headers": {
+        "RSC": 1,
+        "Next-Router-Prefetch": 1
+      }
+    },
     {
       "path": "/dynamic-index/hello/index",
       "status": 200,