[Flight] model halted references explicitly

using infinitely suspending promises isn't right because this will parse as a promise which is only appropriate if the value we're halting at is a promise. Instead we need to have a special marker type that says this reference will never resolve. Additionally flight client needs to not error any halted references when the stream closes because they will otherwise appear as an error

Author: gnoff

packages/react-client/src/ReactFlightClient.js

@@ -45,6 +45,7 @@ import {
   enableRefAsProp,
   enableFlightReadableStream,
   enableOwnerStacks,
+  enableHalt,
 } from 'shared/ReactFeatureFlags';
 
 import {
@@ -860,6 +861,27 @@ function getChunk(response: Response, id: number): SomeChunk<any> {
   return chunk;
 }
 
+/**
+ * Fork of waitForReference that doesn't ever reslve
+ */
+function waitForever() {
+  let handler: InitializationHandler;
+  if (initializingHandler) {
+    handler = initializingHandler;
+    handler.deps++;
+  } else {
+    handler = initializingHandler = {
+      parent: null,
+      chunk: null,
+      value: null,
+      deps: 1,
+      errored: false,
+    };
+  }
+
+  return null;
+}
+
 function waitForReference<T>(
   referencedChunk: SomeChunk<T>,
   parentObject: Object,
@@ -1227,6 +1249,14 @@ function parseModelString(
         }
         return readTemporaryReference(temporaryReferences, reference);
       }
+      case '&': {
+        if (enableHalt) {
+          return waitForever();
+        }
+        // It'd be an error if this ever happened when this flag is off
+        // but that shoudl be impossibe
+        // fallthrough
+      }
       case 'Q': {
         // Map
         const ref = value.slice(2);

packages/react-server/src/ReactFlightServer.js

@@ -615,7 +615,7 @@ function serializeThenable(
         request.abortableTasks.delete(newTask);
         newTask.status = ABORTED;
         if (enableHalt && request.fatalError === haltSymbol) {
-          emitModelChunk(request, newTask.id, reusableInfinitePromiseModel);
+          emitModelChunk(request, newTask.id, reusableHaltedReferenceModel);
         } else {
           const errorId: number = (request.fatalError: any);
           const model = stringify(serializeByValueID(errorId));
@@ -1818,7 +1818,6 @@ function serializeLazyID(id: number): string {
 function serializeInfinitePromise(): string {
   return '$@';
 }
-const reusableInfinitePromiseModel = stringify(serializeInfinitePromise());
 
 function serializePromiseID(id: number): string {
   return '$@' + id.toString(16);
@@ -1836,6 +1835,11 @@ function serializeLimitedObject(): string {
   return '$Y';
 }
 
+function serializeHaltedReference(): string {
+  return '$&';
+}
+const reusableHaltedReferenceModel = '"$&"';
+
 function serializeNumber(number: number): string | number {
   if (Number.isFinite(number)) {
     if (number === 0 && 1 / number === -Infinity) {
@@ -2177,7 +2181,7 @@ function renderModel(
         if (request.status === ABORTING) {
           task.status = ABORTED;
           if (enableHalt && request.fatalError === haltSymbol) {
-            return serializeInfinitePromise();
+            return serializeHaltedReference();
           }
           const errorId: number = (request.fatalError: any);
           if (wasReactNode) {
@@ -2233,7 +2237,7 @@ function renderModel(
     if (request.status === ABORTING) {
       task.status = ABORTED;
       if (enableHalt && request.fatalError === haltSymbol) {
-        return serializeInfinitePromise();
+        return serializeHaltedReference();
       }
       const errorId: number = (request.fatalError: any);
       if (wasReactNode) {
@@ -3725,7 +3729,7 @@ function retryTask(request: Request, task: Task): void {
           request.abortableTasks.delete(task);
           task.status = ABORTED;
           if (enableHalt && request.fatalError === haltSymbol) {
-            emitModelChunk(request, task.id, reusableInfinitePromiseModel);
+            emitModelChunk(request, task.id, reusableHaltedReferenceModel);
           } else {
             const errorId: number = (request.fatalError: any);
             const model = stringify(serializeByValueID(errorId));
@@ -3753,7 +3757,7 @@ function retryTask(request: Request, task: Task): void {
       request.abortableTasks.delete(task);
       task.status = ABORTED;
       if (enableHalt && request.fatalError === haltSymbol) {
-        emitModelChunk(request, task.id, reusableInfinitePromiseModel);
+        emitModelChunk(request, task.id, reusableHaltedReferenceModel);
       } else {
         const errorId: number = (request.fatalError: any);
         const model = stringify(serializeByValueID(errorId));
@@ -3842,7 +3846,7 @@ function haltTask(task: Task, request: Request): void {
     return;
   }
   task.status = ABORTED;
-  emitModelChunk(request, task.id, reusableInfinitePromiseModel);
+  emitModelChunk(request, task.id, reusableHaltedReferenceModel);
 }
 
 function flushCompletedChunks(