Re-implement Server Action reducer

WIP

Author: acdlite

packages/next/errors.json

@@ -943,5 +943,6 @@
   "942": "Unexpected stream chunk while in Before stage",
   "943": "getFlightStream should always receive a ReadableStream when using the edge runtime",
   "944": "nodeStreamFromReadableStream cannot be used in the edge runtime",
-  "945": "createNodeStreamFromChunks cannot be used in the edge runtime"
+  "945": "createNodeStreamFromChunks cannot be used in the edge runtime",
+  "946": "Internal Next.js error: Missing page segment."
 }

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

@@ -117,6 +117,21 @@ export function createEmptyCacheNode(): CacheNode {
   }
 }
 
+export function clearDynamicDataFromCacheNodeTree(
+  existingCache: CacheNode
+): CacheNode {
+  // Copy all the fields from the root cache node, but none of the children.
+  const clone = createEmptyCacheNode()
+  clone.lazyData = existingCache.lazyData
+  clone.rsc = existingCache.rsc
+  clone.prefetchRsc = existingCache.prefetchRsc
+  clone.head = existingCache.head
+  clone.prefetchHead = existingCache.prefetchHead
+  clone.loading = existingCache.loading
+  clone.navigatedAt = existingCache.navigatedAt
+  return clone
+}
+
 function copyNextJsInternalHistoryState(data: any) {
   if (data == null) data = {}
   const currentState = window.history.state

packages/next/src/client/components/router-reducer/ppr-navigations.ts

@@ -15,7 +15,6 @@ import type {
 } from '../../../shared/lib/app-router-types'
 import { DEFAULT_SEGMENT_KEY } from '../../../shared/lib/segment'
 import { matchSegment } from '../match-segments'
-import { revalidateEntireCache } from '../segment-cache/cache'
 import { createHrefFromUrl } from './create-href-from-url'
 import { createRouterCacheKey } from './create-router-cache-key'
 import {
@@ -111,6 +110,8 @@ export function startPPRNavigation(
   oldCacheNode: CacheNode,
   oldRouterState: FlightRouterState,
   newRouterState: FlightRouterState,
+  seedData: CacheNodeSeedData | null,
+  seedHead: HeadData | null,
   prefetchData: CacheNodeSeedData | null,
   prefetchHead: HeadData | null,
   isPrefetchHeadPartial: boolean,
@@ -125,6 +126,8 @@ export function startPPRNavigation(
     oldRouterState,
     newRouterState,
     false,
+    seedData,
+    seedHead,
     prefetchData,
     prefetchHead,
     isPrefetchHeadPartial,
@@ -137,18 +140,14 @@ export function startPPRNavigation(
 export function startPPRRefresh(
   navigatedAt: number,
   currentRouterState: FlightRouterState,
-  currentNextUrl: string | null,
+  seedData: CacheNodeSeedData | null,
+  seedHead: HeadData | null,
   accumulation: NavigationRequestAccumulation
 ): Task | null {
   // A refresh is a special case of a navigation where all the dynamic data in
   // the page is re-fetched. There is no "shared layout" to consider because
   // the route hasn't changed.
 
-  // TODO: Currently, all refreshes purge the prefetch cache. In the future,
-  // only client-side refreshes will have this behavior; the server-side
-  // `refresh` should send new data without purging the prefetch cache.
-  revalidateEntireCache(currentNextUrl, currentRouterState)
-
   // TODO: Currently refreshes do not read from the prefetch cache, as in the
   // pre-Segment Cache implementation. This will be added in a subsequent PR.
   const prefetchData = null
@@ -167,6 +166,8 @@ export function startPPRRefresh(
     navigatedAt,
     currentRouterState,
     existingCacheNode,
+    seedData,
+    seedHead,
     prefetchData,
     prefetchHead,
     isPrefetchHeadPartial,
@@ -182,6 +183,8 @@ function updateCacheNodeOnNavigation(
   oldRouterState: FlightRouterState,
   newRouterState: FlightRouterState,
   didFindRootLayout: boolean,
+  seedData: CacheNodeSeedData | null,
+  seedHead: HeadData | null,
   prefetchData: CacheNodeSeedData | null,
   prefetchHead: HeadData | null,
   isPrefetchHeadPartial: boolean,
@@ -192,6 +195,7 @@ function updateCacheNodeOnNavigation(
   // Diff the old and new trees to reuse the shared layouts.
   const oldRouterStateChildren = oldRouterState[1]
   const newRouterStateChildren = newRouterState[1]
+  const seedDataChildren = seedData !== null ? seedData[1] : null
   const prefetchDataChildren = prefetchData !== null ? prefetchData[1] : null
 
   if (!didFindRootLayout) {
@@ -257,9 +261,13 @@ function updateCacheNodeOnNavigation(
     const oldRouterStateChild: FlightRouterState | void =
       oldRouterStateChildren[parallelRouteKey]
     const oldSegmentMapChild = oldParallelRoutes.get(parallelRouteKey)
+    const seedDataChild: CacheNodeSeedData | void | null =
+      seedDataChildren !== null
+        ? (seedDataChildren[parallelRouteKey] ?? null)
+        : null
     const prefetchDataChild: CacheNodeSeedData | void | null =
       prefetchDataChildren !== null
-        ? prefetchDataChildren[parallelRouteKey]
+        ? (prefetchDataChildren[parallelRouteKey] ?? null)
         : null
 
     const newSegmentChild = newRouterStateChild[0]
@@ -299,7 +307,9 @@ function updateCacheNodeOnNavigation(
           newRouterStateChild,
           oldCacheNodeChild,
           didFindRootLayout,
-          prefetchDataChild !== undefined ? prefetchDataChild : null,
+          seedDataChild,
+          seedHead,
+          prefetchDataChild,
           prefetchHead,
           isPrefetchHeadPartial,
           newSegmentPathChild,
@@ -340,7 +350,9 @@ function updateCacheNodeOnNavigation(
         newRouterStateChild,
         oldCacheNodeChild,
         didFindRootLayout,
-        prefetchDataChild !== undefined ? prefetchDataChild : null,
+        seedDataChild,
+        seedHead,
+        prefetchDataChild,
         prefetchHead,
         isPrefetchHeadPartial,
         newSegmentPathChild,
@@ -364,6 +376,8 @@ function updateCacheNodeOnNavigation(
           oldRouterStateChild,
           newRouterStateChild,
           didFindRootLayout,
+          seedDataChild,
+          seedHead,
           prefetchDataChild,
           prefetchHead,
           isPrefetchHeadPartial,
@@ -380,7 +394,9 @@ function updateCacheNodeOnNavigation(
           newRouterStateChild,
           oldCacheNodeChild,
           didFindRootLayout,
-          prefetchDataChild !== undefined ? prefetchDataChild : null,
+          seedDataChild,
+          seedHead,
+          prefetchDataChild,
           prefetchHead,
           isPrefetchHeadPartial,
           newSegmentPathChild,
@@ -395,7 +411,9 @@ function updateCacheNodeOnNavigation(
         newRouterStateChild,
         oldCacheNodeChild,
         didFindRootLayout,
-        prefetchDataChild !== undefined ? prefetchDataChild : null,
+        seedDataChild,
+        seedHead,
+        prefetchDataChild,
         prefetchHead,
         isPrefetchHeadPartial,
         newSegmentPathChild,
@@ -495,6 +513,8 @@ function beginRenderingNewRouteTree(
   newRouterState: FlightRouterState,
   existingCacheNode: CacheNode | void,
   didFindRootLayout: boolean,
+  seedData: CacheNodeSeedData | null,
+  seedHead: HeadData | null,
   prefetchData: CacheNodeSeedData | null,
   possiblyPartialPrefetchHead: HeadData | null,
   isPrefetchHeadPartial: boolean,
@@ -537,6 +557,8 @@ function beginRenderingNewRouteTree(
     navigatedAt,
     newRouterState,
     existingCacheNode,
+    seedData,
+    seedHead,
     prefetchData,
     possiblyPartialPrefetchHead,
     isPrefetchHeadPartial,
@@ -551,6 +573,8 @@ function createCacheNodeOnNavigation(
   navigatedAt: number,
   routerState: FlightRouterState,
   existingCacheNode: CacheNode | void,
+  seedData: CacheNodeSeedData | null,
+  seedHead: HeadData | null,
   prefetchData: CacheNodeSeedData | null,
   possiblyPartialPrefetchHead: HeadData | null,
   isPrefetchHeadPartial: boolean,
@@ -597,7 +621,22 @@ function createCacheNodeOnNavigation(
   let loading: LoadingModuleData | Promise<LoadingModuleData>
   let head: HeadData | null
   let cacheNodeNavigatedAt: number
-  if (
+  if (seedData !== null) {
+    // When navigating in response to a Server Action, the server may send back
+    // RSC data alongside the action body response. If so, we can use this data
+    // directly without consulting the client cache and without triggering a new
+    // request from the server.
+    // TODO: Since Server Action responses are streaming, we may not be able to
+    // render the UI immediately, even though we already have a reference to it
+    // here. It's worth checking the prefetch cache to see if there's a partial
+    // state we can show in the meantime. We'll implement this once this module
+    // is updated to access the prefetch cache directly, instead of passing it
+    // down via the CacheNodeSeedData type.
+    rsc = seedData[0]
+    loading = seedData[2]
+    head = isLeafSegment ? seedHead : null
+    cacheNodeNavigatedAt = navigatedAt
+  } else if (
     existingCacheNode !== undefined &&
     // DYNAMIC_STALETIME_MS defaults to 0, but it can be increased using
     // the experimental.staleTimes.dynamic config. When set, we'll avoid
@@ -673,6 +712,7 @@ function createCacheNodeOnNavigation(
   // new one from the server. Keep traversing down the tree until we reach
   // something that requires a dynamic request.
   const prefetchDataChildren = prefetchData !== null ? prefetchData[1] : null
+  const seedDataChildren = seedData !== null ? seedData[1] : null
   const taskChildren = new Map()
   const existingCacheNodeChildren =
     existingCacheNode !== undefined ? existingCacheNode.parallelRoutes : null
@@ -693,9 +733,13 @@ function createCacheNodeOnNavigation(
     for (let parallelRouteKey in routerStateChildren) {
       const routerStateChild: FlightRouterState =
         routerStateChildren[parallelRouteKey]
-      const prefetchDataChild: CacheNodeSeedData | void | null =
+      const seedDataChild: CacheNodeSeedData | null =
+        seedDataChildren !== null
+          ? (seedDataChildren[parallelRouteKey] ?? null)
+          : null
+      const prefetchDataChild: CacheNodeSeedData | null =
         prefetchDataChildren !== null
-          ? prefetchDataChildren[parallelRouteKey]
+          ? (prefetchDataChildren[parallelRouteKey] ?? null)
           : null
       const existingSegmentMapChild =
         existingCacheNodeChildren !== null
@@ -719,6 +763,8 @@ function createCacheNodeOnNavigation(
         navigatedAt,
         routerStateChild,
         existingCacheNodeChild,
+        seedDataChild,
+        seedHead,
         prefetchDataChild,
         possiblyPartialPrefetchHead,
         isPrefetchHeadPartial,

packages/next/src/client/components/router-reducer/reducers/navigate-reducer.ts

@@ -164,18 +164,24 @@ export function navigateReducer(
     return handleExternalUrl(state, mutable, href, pendingPush)
   }
 
-  // Temporary glue code between the router reducer and the new navigation
-  // implementation. Eventually we'll rewrite the router reducer to a
-  // state machine.
   const currentUrl = new URL(state.canonicalUrl, location.origin)
+  const seedRoute = null
+  const seedData = null
+  const seedHead = null
   const result = navigateUsingSegmentCache(
     url,
     currentUrl,
     state.cache,
     state.tree,
     state.nextUrl,
+    seedRoute,
+    seedData,
+    seedHead,
     shouldScroll,
     mutable
   )
+  // Temporary glue code between the router reducer and the new navigation
+  // implementation. Eventually we'll rewrite the router reducer to a
+  // state machine.
   return handleNavigationResult(url, state, mutable, pendingPush, result)
 }

packages/next/src/client/components/router-reducer/reducers/refresh-reducer.ts

@@ -6,18 +6,30 @@ import type {
 } from '../router-reducer-types'
 import { handleNavigationResult } from './navigate-reducer'
 import { refresh as refreshUsingSegmentCache } from '../../segment-cache/navigation'
+import { revalidateEntireCache } from '../../segment-cache/cache'
 
 export function refreshReducer(
   state: ReadonlyReducerState,
   action: RefreshAction
 ): ReducerState {
+  // Client-initiated refreshes (router.refresh()) purge the entire
+  // prefetch cache. This is unlike the Server Action-based refresh(), which
+  // only purges the dynamic data cache.
+  const currentNextUrl = state.nextUrl
+  const currentRouterState = state.tree
+  revalidateEntireCache(currentNextUrl, currentRouterState)
+
   const currentUrl = new URL(state.canonicalUrl, action.origin)
+  const seedData = null
+  const seedHead = null
   const result = refreshUsingSegmentCache(
     currentUrl,
-    state.tree,
-    state.nextUrl,
+    currentRouterState,
+    currentNextUrl,
     state.renderedSearch,
-    state.canonicalUrl
+    state.canonicalUrl,
+    seedData,
+    seedHead
   )
 
   const mutable: Mutable = {}