Unwrap promise with experimental_use

packages/next/client/app-index.tsx

@@ -14,6 +14,8 @@ declare global {
   const __webpack_require__: any
 }
 
+const use = (React as any).experimental_use
+
 // eslint-disable-next-line no-undef
 const getChunkScriptFilename = __webpack_require__.u
 const chunkFilenameMap: any = {}
@@ -143,7 +145,7 @@ function ServerRoot({ cacheKey }: { cacheKey: string }) {
     rscCache.delete(cacheKey)
   })
   const response = useInitialServerResponse(cacheKey)
-  const root = response.readRoot()
+  const root = use(response)
   return root
 }
 

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

@@ -65,8 +65,8 @@ export function fetchServerResponse(
   url: URL,
   flightRouterState: FlightRouterState,
   prefetch?: true
-): { readRoot: () => FlightData } {
-  // Handle the `fetch` readable stream that can be read using `readRoot`.
+): Promise<FlightData> {
+  // Handle the `fetch` readable stream that can be unwrapped by `React.use`.
   return createFromReadableStream(fetchFlight(url, flightRouterState, prefetch))
 }
 
@@ -212,20 +212,15 @@ export default function AppRouter({
             window.history.state?.tree || initialTree,
             true
           )
-          try {
-            r.readRoot()
-          } catch (e) {
-            await e
-            const flightData = r.readRoot()
-            // @ts-ignore startTransition exists
-            React.startTransition(() => {
-              dispatch({
-                type: ACTION_PREFETCH,
-                url,
-                flightData,
-              })
+          const flightData = await r
+          // @ts-ignore startTransition exists
+          React.startTransition(() => {
+            dispatch({
+              type: ACTION_PREFETCH,
+              url,
+              flightData,
             })
-          }
+          })
         } catch (err) {
           console.error('PREFETCH ERROR', err)
         }

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

@@ -17,6 +17,8 @@ import {
 import { fetchServerResponse } from './app-router.client'
 // import { matchSegment } from './match-segments'
 
+const use = (React as any).experimental_use
+
 /**
  * Check if every segment in array a and b matches
  */
@@ -218,14 +220,14 @@ export function InnerLayoutRouter({
     throw new Error('Child node should not have both subTreeData and data')
   }
 
-  // If cache node has a data request we have to readRoot and update the cache.
+  // If cache node has a data request we have to unwrap response by `use` and update the cache.
   if (childNode.data) {
     // TODO-APP: error case
     /**
      * Flight response data
      */
-    // When the data has not resolved yet readRoot will suspend here.
-    const flightData = childNode.data.readRoot()
+    // When the data has not resolved yet `use` will suspend here.
+    const flightData = use(childNode.data)
 
     // Handle case when navigating to page in `pages` from `app`
     if (typeof flightData === 'string') {

packages/next/client/components/reducer.ts

@@ -6,9 +6,12 @@ import type {
   FlightSegmentPath,
   Segment,
 } from '../../server/app-render'
+import React from 'react'
 import { matchSegment } from './match-segments'
 import { fetchServerResponse } from './app-router.client'
 
+const use = (React as any).experimental_use
+
 /**
  * Invalidate cache one level down from the router state.
  */
@@ -730,8 +733,7 @@ export function reducer(
           cache,
           state.cache,
           segments.slice(1),
-          (): { readRoot: () => FlightData } =>
-            fetchServerResponse(url, optimisticTree)
+          (): Promise<FlightData> => fetchServerResponse(url, optimisticTree)
         )
 
         // If optimistic fetch couldn't happen it falls back to the non-optimistic case.
@@ -761,8 +763,8 @@ export function reducer(
         cache.data = fetchServerResponse(url, state.tree)
       }
 
-      // readRoot to suspend here (in the reducer) until the fetch resolves.
-      const flightData = cache.data.readRoot()
+      // Unwrap cache data with `use` to suspend here (in the reducer) until the fetch resolves.
+      const flightData = use(cache.data)
 
       // Handle case when navigating to page in `pages` from `app`
       if (typeof flightData === 'string') {
@@ -953,7 +955,7 @@ export function reducer(
           'refetch',
         ])
       }
-      const flightData = cache.data.readRoot()
+      const flightData = use(cache.data)
 
       // Handle case when navigating to page in `pages` from `app`
       if (typeof flightData === 'string') {

packages/next/compiled/react-server-dom-webpack/cjs/react-server-dom-webpack-writer.browser.development.server.js

@@ -162,6 +162,7 @@ function processErrorChunk(request, id, message, stack) {
   return stringToChunk(row);
 }
 function processModelChunk(request, id, model) {
+  // $FlowFixMe: `json` might be `undefined` when model is a symbol.
   var json = stringify(model, request.toJSON);
   var row = serializeRowHeader('J', id) + json + '\n';
   return stringToChunk(row);
@@ -172,6 +173,7 @@ function processReferenceChunk(request, id, reference) {
   return stringToChunk(row);
 }
 function processModuleChunk(request, id, moduleMetaData) {
+  // $FlowFixMe: `json` might be `undefined` when moduleMetaData is a symbol.
   var json = stringify(moduleMetaData);
   var row = serializeRowHeader('M', id) + json + '\n';
   return stringToChunk(row);
@@ -894,8 +896,8 @@ function readContext(context) {
   return value;
 }
 
-// Corresponds to ReactFiberWakeable module. Generally, changes to one module
-// should be reflected in the other.
+// Corresponds to ReactFiberWakeable and ReactFizzWakeable modules. Generally,
+// changes to one module should be reflected in the others.
 // TODO: Rename this module and the corresponding Fiber one to "Thenable"
 // instead of "Wakeable". Or some other more appropriate name.
 // TODO: Sparse arrays are bad for performance.
@@ -917,11 +919,6 @@ function trackSuspendedWakeable(wakeable) {
   // a listener that will update its status and result when it resolves.
 
   switch (thenable.status) {
-    case 'pending':
-      // Since the status is already "pending", we can assume it will be updated
-      // when it resolves, either by React or something in userspace.
-      break;
-
     case 'fulfilled':
     case 'rejected':
       // A thenable that already resolved shouldn't have been thrown, so this is
@@ -933,9 +930,13 @@ function trackSuspendedWakeable(wakeable) {
 
     default:
       {
-        // TODO: Only instrument the thenable if the status if not defined. If
-        // it's defined, but an unknown value, assume it's been instrumented by
-        // some custom userspace implementation.
+        if (typeof thenable.status === 'string') {
+          // Only instrument the thenable if the status if not defined. If
+          // it's defined, but an unknown value, assume it's been instrumented by
+          // some custom userspace implementation. We treat it as "pending".
+          break;
+        }
+
         var pendingThenable = thenable;
         pendingThenable.status = 'pending';
         pendingThenable.then(function (fulfilledValue) {
@@ -990,7 +991,9 @@ function prepareToUseHooksForComponent(prevThenableState) {
   thenableState = prevThenableState;
 }
 function getThenableStateAfterSuspending() {
-  return thenableState;
+  var state = thenableState;
+  thenableState = null;
+  return state;
 }
 
 function readContext$1(context) {
@@ -1149,6 +1152,9 @@ function use(usable) {
             }
           }
       }
+    } else if (usable.$$typeof === REACT_SERVER_CONTEXT_TYPE) {
+      var context = usable;
+      return readContext$1(context);
     }
   } // eslint-disable-next-line react-internal/safe-string-coercion
 
@@ -1159,7 +1165,8 @@ function use(usable) {
 var ContextRegistry = ReactSharedInternals.ContextRegistry;
 function getOrCreateServerContext(globalName) {
   if (!ContextRegistry[globalName]) {
-    ContextRegistry[globalName] = React.createServerContext(globalName, REACT_SERVER_CONTEXT_DEFAULT_VALUE_NOT_LOADED);
+    ContextRegistry[globalName] = React.createServerContext(globalName, // $FlowFixMe function signature doesn't reflect the symbol value
+    REACT_SERVER_CONTEXT_DEFAULT_VALUE_NOT_LOADED);
   }
 
   return ContextRegistry[globalName];
@@ -1292,7 +1299,8 @@ function attemptResolveElement(type, key, ref, props, prevThenableState) {
             if (extraKeys.length !== 0) {
               error('ServerContext can only have a value prop and children. Found: %s', JSON.stringify(extraKeys));
             }
-          }
+          } // $FlowFixMe issue discovered when updating Flow
+
 
           return [REACT_ELEMENT_TYPE, type, key, // Rely on __popProvider being serialized last to pop the provider.
           {
@@ -1677,7 +1685,8 @@ function resolveModelToJSON(request, parent, key, value) {
           }
         }
       }
-    }
+    } // $FlowFixMe
+
 
     return value;
   }
@@ -1708,12 +1717,14 @@ function resolveModelToJSON(request, parent, key, value) {
 
     if (existingId !== undefined) {
       return serializeByValueID(existingId);
-    }
+    } // $FlowFixMe `description` might be undefined
+
 
-    var name = value.description;
+    var name = value.description; // $FlowFixMe `name` might be undefined
 
     if (Symbol.for(name) !== value) {
-      throw new Error('Only global symbols received from Symbol.for(...) can be passed to client components. ' + ("The symbol Symbol.for(" + value.description + ") cannot be found among global symbols. ") + ("Remove " + describeKeyForErrorMessage(key) + " from this object, or avoid the entire object: " + describeObjectForErrorMessage(parent)));
+      throw new Error('Only global symbols received from Symbol.for(...) can be passed to client components. ' + ("The symbol Symbol.for(" + // $FlowFixMe `description` might be undefined
+      value.description + ") cannot be found among global symbols. ") + ("Remove " + describeKeyForErrorMessage(key) + " from this object, or avoid the entire object: " + describeObjectForErrorMessage(parent)));
     }
 
     request.pendingChunks++;
@@ -1772,6 +1783,7 @@ function emitErrorChunk(request, id, error) {
 }
 
 function emitModuleChunk(request, id, moduleMetaData) {
+  // $FlowFixMe ModuleMetaData is not a ReactModel
   var processedChunk = processModuleChunk(request, id, moduleMetaData);
   request.completedModuleChunks.push(processedChunk);
 }