fix router crash on revalidate + popstate

packages/next/src/client/components/app-router.tsx

@@ -183,6 +183,7 @@ export function createEmptyCacheNode(): CacheNode {
     rsc: null,
     prefetchRsc: null,
     parallelRoutes: new Map(),
+    lazyDataResolved: false,
   }
 }
 
@@ -578,7 +579,6 @@ function Router({
         return
       }
 
-      // @ts-ignore useTransition exists
       // TODO-APP: Ideally the back button should not use startTransition as it should apply the updates synchronously
       // Without startTransition works if the cache is there for this path
       startTransition(() => {

packages/next/src/client/components/layout-router.tsx

@@ -355,6 +355,7 @@ function InnerLayoutRouter({
       prefetchRsc: null,
       head: null,
       parallelRoutes: new Map(),
+      lazyDataResolved: false,
     }
 
     /**
@@ -411,6 +412,7 @@ function InnerLayoutRouter({
         context.nextUrl,
         buildId
       )
+      childNode.lazyDataResolved = false
     }
 
     /**
@@ -419,15 +421,22 @@ function InnerLayoutRouter({
     // When the data has not resolved yet `use` will suspend here.
     const serverResponse = use(lazyData)
 
-    // setTimeout is used to start a new transition during render, this is an intentional hack around React.
-    setTimeout(() => {
-      startTransition(() => {
-        changeByServerResponse({
-          previousTree: fullTree,
-          serverResponse,
+    if (!childNode.lazyDataResolved) {
+      // setTimeout is used to start a new transition during render, this is an intentional hack around React.
+      setTimeout(() => {
+        startTransition(() => {
+          changeByServerResponse({
+            previousTree: fullTree,
+            serverResponse,
+          })
         })
       })
-    })
+
+      // It's important that we mark this as resolved, in case this branch is replayed, we don't want to continously re-apply
+      // the patch to the tree.
+      childNode.lazyDataResolved = true
+    }
+
     // Suspend infinitely as `changeByServerResponse` will cause a different part of the tree to be rendered.
     use(createInfinitePromise()) as never
   }

packages/next/src/shared/lib/app-router-context.shared-runtime.ts

@@ -17,6 +17,11 @@ export type ChildSegmentMap = Map<string, CacheNode>
 export type CacheNode = ReadyCacheNode | LazyCacheNode
 
 export type LazyCacheNode = {
+  /**
+   * Whether the lazy cache node data promise has been resolved.
+   * This value is only true after we've called `use` on the promise (and applied the data to the tree).
+   */
+  lazyDataResolved?: boolean
   /**
    * When rsc is null, this is a lazily-initialized cache node.
    *
@@ -59,6 +64,11 @@ export type LazyCacheNode = {
 }
 
 export type ReadyCacheNode = {
+  /**
+   * Whether the lazy cache node data promise has been resolved.
+   * This value is only true after we've called `use` on the promise (and applied the data to the tree).
+   */
+  lazyDataResolved?: boolean
   /**
    * When rsc is not null, it represents the RSC data for the
    * corresponding segment.

packages/next/src/shared/lib/router/action-queue.ts

@@ -140,8 +140,8 @@ function dispatchAction(
   const newAction: ActionQueueNode = {
     payload,
     next: null,
-    resolve: resolvers!.resolve,
-    reject: resolvers!.reject,
+    resolve: resolvers.resolve,
+    reject: resolvers.reject,
   }
 
   // Check if the queue is empty

test/e2e/app-dir/navigation/app/popstate-revalidate/foo/action.ts

@@ -0,0 +1,8 @@
+'use server'
+
+import { revalidatePath } from 'next/cache'
+
+export async function action() {
+  revalidatePath('/', 'layout')
+  return true
+}

test/e2e/app-dir/navigation/app/popstate-revalidate/foo/page.tsx

@@ -0,0 +1,20 @@
+'use client'
+
+import { useFormState } from 'react-dom'
+import { action } from './action'
+
+export default function Page() {
+  const [submitted, formAction] = useFormState(action, false)
+  if (submitted) {
+    return <div>Form Submitted.</div>
+  }
+
+  return (
+    <div>
+      <h1>Form</h1>
+      <form action={formAction}>
+        <button id="submit-button">Push this button to submit the form</button>
+      </form>
+    </div>
+  )
+}

test/e2e/app-dir/navigation/app/popstate-revalidate/page.tsx

@@ -0,0 +1,12 @@
+import Link from 'next/link'
+
+export default async function Home() {
+  await new Promise((resolve) => setTimeout(resolve, 1500))
+
+  return (
+    <div>
+      <h1>Home</h1>
+      <Link href="/popstate-revalidate/foo">To /foo</Link>
+    </div>
+  )
+}

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

@@ -862,5 +862,28 @@ createNextDescribe(
         })
       })
     })
+
+    describe('browser back to a revalidated page', () => {
+      it('should load the page', async () => {
+        const browser = await next.browser('/popstate-revalidate')
+        expect(await browser.elementByCss('h1').text()).toBe('Home')
+        await browser.elementByCss("[href='/popstate-revalidate/foo']").click()
+        await browser.waitForElementByCss('#submit-button')
+        expect(await browser.elementByCss('h1').text()).toBe('Form')
+        await browser.elementById('submit-button').click()
+
+        await retry(async () => {
+          expect(await browser.elementByCss('body').text()).toContain(
+            'Form Submitted.'
+          )
+        })
+
+        await browser.back()
+
+        await retry(async () => {
+          expect(await browser.elementByCss('h1').text()).toBe('Home')
+        })
+      })
+    })
   }
 )