Use provided waitUntil for pending revalidates (#74164)

Currently we are using `pendingWaitUntil` on `renderOpts` to handle
pending revalidations (fetch updates and revalidate tag calls). This
uses our old strategy of `waitUntil` inside of `sendResponse` which just
keeps the stream open until the promise resolves. This isn't ideal if we
have a proper waitUntil strategy provided so this updates to ensure we
use that instead if available.

Also adds some debug logs so we can track when this pending revalidates
promise is resolved.

Author: ijjk

packages/next/src/server/app-render/app-render.tsx

@@ -1298,13 +1298,23 @@ async function renderToHTMLOrFlightImpl(
       workStore.pendingRevalidateWrites ||
       workStore.revalidatedTags
     ) {
-      options.waitUntil = Promise.all([
+      const pendingPromise = Promise.all([
         workStore.incrementalCache?.revalidateTag(
           workStore.revalidatedTags || []
         ),
         ...Object.values(workStore.pendingRevalidates || {}),
         ...(workStore.pendingRevalidateWrites || []),
-      ])
+      ]).finally(() => {
+        if (process.env.NEXT_PRIVATE_DEBUG_CACHE) {
+          console.log('pending revalidates promise finished for:', url)
+        }
+      })
+
+      if (renderOpts.waitUntil) {
+        renderOpts.waitUntil(pendingPromise)
+      } else {
+        options.waitUntil = pendingPromise
+      }
     }
 
     if (response.collectedTags) {
@@ -1455,13 +1465,23 @@ async function renderToHTMLOrFlightImpl(
       workStore.pendingRevalidateWrites ||
       workStore.revalidatedTags
     ) {
-      options.waitUntil = Promise.all([
+      const pendingPromise = Promise.all([
         workStore.incrementalCache?.revalidateTag(
           workStore.revalidatedTags || []
         ),
         ...Object.values(workStore.pendingRevalidates || {}),
         ...(workStore.pendingRevalidateWrites || []),
-      ])
+      ]).finally(() => {
+        if (process.env.NEXT_PRIVATE_DEBUG_CACHE) {
+          console.log('pending revalidates promise finished for:', url)
+        }
+      })
+
+      if (renderOpts.waitUntil) {
+        renderOpts.waitUntil(pendingPromise)
+      } else {
+        options.waitUntil = pendingPromise
+      }
     }
 
     // Create the new render result for the response.

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

@@ -2541,6 +2541,16 @@ export default abstract class Server<
 
               return cacheEntry
             }
+            let pendingWaitUntil = context.renderOpts.pendingWaitUntil
+
+            // Attempt using provided waitUntil if available
+            // if it's not we fallback to sendResponse's handling
+            if (pendingWaitUntil) {
+              if (context.renderOpts.waitUntil) {
+                context.renderOpts.waitUntil(pendingWaitUntil)
+                pendingWaitUntil = undefined
+              }
+            }
 
             // Send the response now that we have copied it into the cache.
             await sendResponse(

packages/next/src/server/route-modules/app-route/module.ts

@@ -597,7 +597,14 @@ export class AppRouteRouteModule extends RouteModule<
         workStore.revalidatedTags || []
       ),
       ...Object.values(workStore.pendingRevalidates || {}),
-    ])
+    ]).finally(() => {
+      if (process.env.NEXT_PRIVATE_DEBUG_CACHE) {
+        console.log(
+          'pending revalidates promise finished for:',
+          requestStore.url
+        )
+      }
+    })
 
     if (prerenderStore) {
       context.renderOpts.collectedTags = prerenderStore.tags?.join(',')

test/e2e/app-dir/app-fetch-deduping/app-fetch-deduping.test.ts

@@ -1,4 +1,4 @@
-import { findPort, waitFor } from 'next-test-utils'
+import { findPort, retry } from 'next-test-utils'
 import http from 'http'
 import url from 'url'
 import { outdent } from 'outdent'
@@ -112,11 +112,10 @@ describe('app-fetch-deduping', () => {
         expect(invocation(next.cliOutput)).toBe(1)
 
         // wait for the revalidation to finish
-        await waitFor(revalidate * 1000 + 1000)
-
-        await next.render('/test')
-
-        expect(invocation(next.cliOutput)).toBe(2)
+        await retry(async () => {
+          await next.render('/test')
+          expect(invocation(next.cliOutput)).toBe(2)
+        }, 10_000)
       })
     })
   } else {