[Flight] Serialize already resolved Promises as debug models (#33588)

We already support serializing the values of instrumented Promises as
debug values such as in console logs. However, we don't support plain
native promises.

This waits a microtask to see if we can read the value within a
microtask and if so emit it. This is so that we can still close the
connection.

Otherwise, we emit a "halted" row into its row id which replaces the old
"Infinite Promise" reference.

We could potentially wait until the end of the render before cancelling
so that if it resolves before we exit we can still include its value but
that would require a bit more work. Ideally we'd have a way to get these
lazily later anyway.

Author: sebmarkbage

packages/react-client/src/ReactFlightClient.js

@@ -155,6 +155,7 @@ const RESOLVED_MODEL = 'resolved_model';
 const RESOLVED_MODULE = 'resolved_module';
 const INITIALIZED = 'fulfilled';
 const ERRORED = 'rejected';
+const HALTED = 'halted'; // DEV-only. Means it never resolves even if connection closes.
 
 type PendingChunk<T> = {
   status: 'pending',
@@ -221,13 +222,23 @@ type ErroredChunk<T> = {
   _debugInfo?: null | ReactDebugInfo, // DEV-only
   then(resolve: (T) => mixed, reject?: (mixed) => mixed): void,
 };
+type HaltedChunk<T> = {
+  status: 'halted',
+  value: null,
+  reason: null,
+  _response: Response,
+  _children: Array<SomeChunk<any>> | ProfilingResult, // Profiling-only
+  _debugInfo?: null | ReactDebugInfo, // DEV-only
+  then(resolve: (T) => mixed, reject?: (mixed) => mixed): void,
+};
 type SomeChunk<T> =
   | PendingChunk<T>
   | BlockedChunk<T>
   | ResolvedModelChunk<T>
   | ResolvedModuleChunk<T>
   | InitializedChunk<T>
-  | ErroredChunk<T>;
+  | ErroredChunk<T>
+  | HaltedChunk<T>;
 
 // $FlowFixMe[missing-this-annot]
 function ReactPromise(
@@ -311,6 +322,9 @@ ReactPromise.prototype.then = function <T>(
         chunk.reason.push(reject);
       }
       break;
+    case HALTED: {
+      break;
+    }
     default:
       if (reject) {
         reject(chunk.reason);
@@ -368,6 +382,7 @@ function readChunk<T>(chunk: SomeChunk<T>): T {
       return chunk.value;
     case PENDING:
     case BLOCKED:
+    case HALTED:
       // eslint-disable-next-line no-throw-literal
       throw ((chunk: any): Thenable<T>);
     default:
@@ -1367,6 +1382,7 @@ function getOutlinedModel<T>(
       return chunkValue;
     case PENDING:
     case BLOCKED:
+    case HALTED:
       return waitForReference(chunk, parentObject, key, response, map, path);
     default:
       // This is an error. Instead of erroring directly, we're going to encode this on
@@ -1470,10 +1486,6 @@ function parseModelString(
       }
       case '@': {
         // Promise
-        if (value.length === 2) {
-          // Infinite promise that never resolves.
-          return new Promise(() => {});
-        }
         const id = parseInt(value.slice(2), 16);
         const chunk = getChunk(response, id);
         if (enableProfilerTimer && enableComponentPerformanceTrack) {
@@ -1769,6 +1781,22 @@ export function createResponse(
   );
 }
 
+function resolveDebugHalt(response: Response, id: number): void {
+  const chunks = response._chunks;
+  let chunk = chunks.get(id);
+  if (!chunk) {
+    chunks.set(id, (chunk = createPendingChunk(response)));
+  } else {
+  }
+  if (chunk.status !== PENDING && chunk.status !== BLOCKED) {
+    return;
+  }
+  const haltedChunk: HaltedChunk<any> = (chunk: any);
+  haltedChunk.status = HALTED;
+  haltedChunk.value = null;
+  haltedChunk.reason = null;
+}
+
 function resolveModel(
   response: Response,
   id: number,
@@ -3339,6 +3367,10 @@ function processFullStringRow(
     }
     // Fallthrough
     default: /* """ "{" "[" "t" "f" "n" "0" - "9" */ {
+      if (__DEV__ && row === '') {
+        resolveDebugHalt(response, id);
+        return;
+      }
       // We assume anything else is JSON.
       resolveModel(response, id, row);
       return;

packages/react-client/src/__tests__/ReactFlight-test.js

@@ -3213,7 +3213,8 @@ describe('ReactFlight', () => {
         prop: 123,
         fn: foo,
         map: new Map([['foo', foo]]),
-        promise: new Promise(() => {}),
+        promise: Promise.resolve('yo'),
+        infinitePromise: new Promise(() => {}),
       });
       throw new Error('err');
     }
@@ -3258,9 +3259,14 @@ describe('ReactFlight', () => {
     });
     ownerStacks = [];
 
+    // Let the Promises resolve.
+    await 0;
+    await 0;
+    await 0;
+
     // The error should not actually get logged because we're not awaiting the root
     // so it's not thrown but the server log also shouldn't be replayed.
-    await ReactNoopFlightClient.read(transport);
+    await ReactNoopFlightClient.read(transport, {close: true});
 
     expect(mockConsoleLog).toHaveBeenCalledTimes(1);
     expect(mockConsoleLog.mock.calls[0][0]).toBe('hi');
@@ -3280,6 +3286,23 @@ describe('ReactFlight', () => {
 
     const promise = mockConsoleLog.mock.calls[0][1].promise;
     expect(promise).toBeInstanceOf(Promise);
+    expect(await promise).toBe('yo');
+
+    const infinitePromise = mockConsoleLog.mock.calls[0][1].infinitePromise;
+    expect(infinitePromise).toBeInstanceOf(Promise);
+    let resolved = false;
+    infinitePromise.then(
+      () => (resolved = true),
+      x => {
+        console.error(x);
+        resolved = true;
+      },
+    );
+    await 0;
+    await 0;
+    await 0;
+    // This should not reject upon aborting the stream.
+    expect(resolved).toBe(false);
 
     expect(ownerStacks).toEqual(['\n    in App (at **)']);
   });

packages/react-noop-renderer/src/ReactNoopFlightClient.js

@@ -24,7 +24,7 @@ type Source = Array<Uint8Array>;
 
 const decoderOptions = {stream: true};
 
-const {createResponse, processBinaryChunk, getRoot} = ReactFlightClient({
+const {createResponse, processBinaryChunk, getRoot, close} = ReactFlightClient({
   createStringDecoder() {
     return new TextDecoder();
   },
@@ -56,6 +56,7 @@ const {createResponse, processBinaryChunk, getRoot} = ReactFlightClient({
 
 type ReadOptions = {|
   findSourceMapURL?: FindSourceMapURLCallback,
+  close?: boolean,
 |};
 
 function read<T>(source: Source, options: ReadOptions): Thenable<T> {
@@ -74,6 +75,9 @@ function read<T>(source: Source, options: ReadOptions): Thenable<T> {
   for (let i = 0; i < source.length; i++) {
     processBinaryChunk(response, source[i], 0);
   }
+  if (options !== undefined && options.close) {
+    close(response);
+  }
   return getRoot(response);
 }