Ensure page.server.js matches correctly

packages/next/server/base-server.ts

@@ -1012,7 +1012,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     const appPathRoutes: Record<string, string> = {}
 
     Object.keys(this.appPathsManifest || {}).forEach((entry) => {
-      appPathRoutes[normalizeAppPath(entry)] = entry
+      appPathRoutes[normalizeAppPath(entry) || '/'] = entry
     })
     return appPathRoutes
   }

packages/next/server/dev/next-dev-server.ts

@@ -337,9 +337,8 @@ export default class DevServer extends Server {
           })
 
           if (isAppPath) {
-            // TODO: should only routes ending in /index.js be route-able?
             const originalPageName = pageName
-            pageName = normalizeAppPath(pageName)
+            pageName = normalizeAppPath(pageName) || '/'
             appPaths[pageName] = originalPageName
 
             if (routedPages.includes(pageName)) {

packages/next/server/get-route-from-entrypoint.ts

@@ -29,6 +29,7 @@ export default function getRouteFromEntrypoint(
 
   if (app) {
     pagePath = matchBundle(APP_ROUTE_NAME_REGEX, entryFile)
+    if (typeof pagePath === 'string' && !pagePath) pagePath = '/'
     if (pagePath) return pagePath
   }
 

test/e2e/app-dir/app-rendering/app/page.server.js

@@ -0,0 +1,3 @@
+export default function Page(props) {
+  return <p>app/page.server.js</p>
+}

test/e2e/app-dir/rendering.test.ts

@@ -31,6 +31,11 @@ describe('views dir rendering', () => {
   })
   afterAll(() => next.destroy())
 
+  it('should serve app/page.server.js at /', async () => {
+    const html = await renderViaHTTP(next.url, '/')
+    expect(html).toContain('app/page.server.js')
+  })
+
   describe('getServerSideProps only', () => {
     it('should run getServerSideProps in layout and page', async () => {
       const html = await renderViaHTTP(