Fix missing cache-control on SSR app route (#70265)

This removes an inaccurate check that doesn't set a revalidate value if
revalidate is `undefined` which can be the case for SSR app route pages.
Also adds a regression test to ensure this doesn't break again.

Fixes: #70213
# Conflicts:
#	packages/next/src/server/base-server.ts

Author: ijjk

packages/next/src/server/base-server.ts

@@ -2638,10 +2638,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
       opts.experimental.ppr
     ) {
       revalidate = 0
-    } else if (
-      typeof cacheEntry.revalidate !== 'undefined' &&
-      (!this.renderOpts.dev || (hasServerProps && !isNextDataRequest))
-    ) {
+    } else if (!this.renderOpts.dev || (hasServerProps && !isNextDataRequest)) {
       // If this is a preview mode request, we shouldn't cache it. We also don't
       // cache 404 pages.
       if (isPreviewMode || (is404Page && !isNextDataRequest)) {

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

@@ -36,6 +36,18 @@ describe('app dir - basic', () => {
     })
   }
 
+  if (isNextStart) {
+    it('should have correct cache-control for SSR routes', async () => {
+      for (const path of ['/catch-all/first', '/ssr']) {
+        const res = await next.fetch(path)
+        expect(res.status).toBe(200)
+        expect(res.headers.get('Cache-Control')).toBe(
+          'private, no-cache, no-store, max-age=0, must-revalidate'
+        )
+      }
+    })
+  }
+
   if (process.env.NEXT_EXPERIMENTAL_COMPILE) {
     it('should provide query for getStaticProps page correctly', async () => {
       const res = await next.fetch('/ssg?hello=world')

test/e2e/app-dir/app/pages/ssr.js

@@ -0,0 +1,16 @@
+import { useRouter } from 'next/router'
+
+export default function Page(props) {
+  return (
+    <>
+      <p>hello from ssr</p>
+      <p id="query">{JSON.stringify(useRouter().query)}</p>
+    </>
+  )
+}
+
+export function getServerSideProps() {
+  return {
+    props: {},
+  }
+}