[next] fix re-mapping logic for index prefetches (#10750)

Follow-up to https://github.com/vercel/vercel/pull/10734 -- but considers that the static prefetch associated with `/` might be inside of a dir such as `index/index.prefetch.rsc`. 

To avoid any future matching conflicts, this PR updates to prefix all static prefetches

.changeset/dry-plants-juggle.md

@@ -0,0 +1,5 @@
+---
+"@vercel/next": patch
+---
+
+fix re-mapping logic for index prefetches

packages/next/src/server-build.ts

@@ -49,6 +49,7 @@ import {
   VariantsManifest,
   RSC_CONTENT_TYPE,
   RSC_PREFETCH_SUFFIX,
+  normalizePrefetches,
 } from './utils';
 import {
   nodeFileTrace,
@@ -193,13 +194,7 @@ export async function serverBuild({
     const rscContentTypeHeader =
       routesManifest?.rsc?.contentTypeHeader || RSC_CONTENT_TYPE;
 
-    // index.{ext} outputs get mapped to `/` which we don't want to override
+    appRscPrefetches = normalizePrefetches(appRscPrefetches);
-    // dynamic routes that aren't pregenerated like the prefetch rsc payload
-    if (appRscPrefetches['index.prefetch.rsc']) {
-      appRscPrefetches['__index.prefetch.rsc'] =
-        appRscPrefetches['index.prefetch.rsc'];
-      delete appRscPrefetches['index.prefetch.rsc'];
-    }
 
     // ensure all appRscPrefetches have a contentType since this is used by Next.js
     // to determine if it's a valid response
@@ -1647,7 +1642,7 @@ export async function serverBuild({
                     dest: path.posix.join(
                       '/',
                       entryDirectory,
-                      `/$1${RSC_PREFETCH_SUFFIX}`
+                      `/__$1${RSC_PREFETCH_SUFFIX}`
                     ),
                     headers: { vary: rscVaryHeader },
                     continue: true,
@@ -1742,7 +1737,7 @@ export async function serverBuild({
               src: `^${path.posix.join(
                 '/',
                 entryDirectory,
-                `/(.+?)${RSC_PREFETCH_SUFFIX}(?:/)?$`
+                `/__(.+?)${RSC_PREFETCH_SUFFIX}(?:/)?$`
               )}`,
               dest: path.posix.join('/', entryDirectory, '/$1.rsc'),
               has: [

packages/next/src/utils.ts

@@ -3120,3 +3120,16 @@ export async function getServerlessPages(params: {
 
   return { pages, appPaths: normalizedAppPaths };
 }
+
+// to avoid any conflict with route matching/resolving, we prefix all prefetches (ie, __index.prefetch.rsc)
+// this is to ensure that prefetches are never matched for things like a greedy match on `index.{ext}`
+export function normalizePrefetches(prefetches: Record<string, FileFsRef>) {
+  const updatedPrefetches: Record<string, FileFsRef> = {};
+
+  for (const key in prefetches) {
+    const newKey = key.replace(/([^/]+\.prefetch\.rsc)$/, '__$1');
+    updatedPrefetches[newKey] = prefetches[key];
+  }
+
+  return updatedPrefetches;
+}

packages/next/test/fixtures/00-app-dir-root-catch-all/app/[[...slug]]/page.js

@@ -1,18 +1,27 @@
+import Link from 'next/link';
+
 export default function Page(props) {
   return (
-    <p>catch-all {JSON.stringify(props.params || {})}</p>
+    <div>
-  )
+      <p>catch-all {JSON.stringify(props.params || {})}</p>
+      <Link href="/">Link to /</Link>
+      <Link href="/index">Link to /index</Link>
+    </div>
+  );
 }
 
 export function generateStaticParams() {
   return [
     {
-      slug: ['']
+      slug: [''],
     },
     {
-      slug: ['first']
+      slug: ['index'],
-    }
+    },
-  ]
+    {
+      slug: ['first'],
+    },
+  ];
 }
 
-export const revalidate = 0
+export const revalidate = 0;

packages/next/test/fixtures/00-app-dir-root-catch-all/app/nested/[[...slug]]/page.js

@@ -0,0 +1,27 @@
+import Link from 'next/link';
+
+export default function Page(props) {
+  return (
+    <div>
+      <p>catch-all {JSON.stringify(props.params || {})}</p>
+      <Link href="/nested">Link to /</Link>
+      <Link href="/nested/index">Link to /index</Link>
+    </div>
+  );
+}
+
+export function generateStaticParams() {
+  return [
+    {
+      slug: [''],
+    },
+    {
+      slug: ['index'],
+    },
+    {
+      slug: ['first'],
+    },
+  ];
+}
+
+export const revalidate = 0;

packages/next/test/fixtures/00-app-dir-root-catch-all/vercel.json

@@ -25,6 +25,63 @@
       "mustNotContain": "<html",
       "mustContain": "catch-all"
     },
+    {
+      "path": "/index",
+      "status": 200,
+      "mustContain": "html"
+    },
+    {
+      "path": "/index",
+      "status": 200,
+      "mustContain": "catch-all"
+    },
+    {
+      "path": "/index",
+      "status": 200,
+      "headers": {
+        "RSC": 1
+      },
+      "mustNotContain": "<html",
+      "mustContain": "catch-all"
+    },
+    {
+      "path": "/nested",
+      "status": 200,
+      "mustContain": "html"
+    },
+    {
+      "path": "/nested",
+      "status": 200,
+      "mustContain": "catch-all"
+    },
+    {
+      "path": "/nested",
+      "status": 200,
+      "headers": {
+        "RSC": 1
+      },
+      "mustNotContain": "<html",
+      "mustContain": "catch-all"
+    },
+    {
+      "path": "/nested/index",
+      "status": 200,
+      "mustContain": "html"
+    },
+    {
+      "path": "/nested/index",
+      "status": 200,
+      "mustContain": "catch-all"
+    },
+    {
+      "path": "/nested/index",
+      "status": 200,
+      "headers": {
+        "RSC": 1
+      },
+      "mustNotContain": "<html",
+      "mustContain": "catch-all"
+    },
     {
       "path": "/first",
       "status": 200,

packages/next/test/unit/utils.test.ts

@@ -7,8 +7,9 @@ import {
   getImagesConfig,
   getNextConfig,
   getServerlessPages,
+  normalizePrefetches,
 } from '../../src/utils';
-import { FileRef } from '@vercel/build-utils';
+import { FileFsRef, FileRef } from '@vercel/build-utils';
 import { genDir } from '../utils';
 
 describe('getNextConfig', () => {
@@ -408,3 +409,27 @@ describe('getServerlessPages', () => {
     expect(Object.keys(appPaths)).toEqual(['favicon.ico.js', 'index.js']);
   });
 });
+
+describe('normalizePrefetches', () => {
+  it('should properly prefix prefetches with `__`', async () => {
+    const dummyFile = new FileFsRef({ fsPath: __dirname });
+
+    const appRscPrefetches = {
+      'index.prefetch.rsc': dummyFile,
+      'index/index.prefetch.rsc': dummyFile,
+      'foo.prefetch.rsc': dummyFile,
+      'foo/index.prefetch.rsc': dummyFile,
+      'foo/bar/baz.prefetch.rsc': dummyFile,
+    };
+
+    const updatedPrefetches = normalizePrefetches(appRscPrefetches);
+
+    expect(Object.keys(updatedPrefetches)).toEqual([
+      '__index.prefetch.rsc',
+      'index/__index.prefetch.rsc',
+      '__foo.prefetch.rsc',
+      'foo/__index.prefetch.rsc',
+      'foo/bar/__baz.prefetch.rsc',
+    ]);
+  });
+});