Add feature flag to use microtasks in the React Native Fabric renderer (#27364)

## Summary

This is part of an effort to align the event loop in React Native with
its behavior on the Web. In this case, we're going to test enabling
microtasks in React Native (Fabric) and we need React to schedule work
using microtasks if available there. This just adds a feature flag to
configure that behavior at runtime.

## How did you test this change?

* Reviewed the generated code, which looks ok.
* Did a manual sync of this PR to Meta's internal infra and tested it
with my changes to enable microtasks in RN/Hermes.

DiffTrain build for commit 54baa79.

Author: rubennorte

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<3cf0c7070b82c229b406663b7dbae937>>
+ * @generated SignedSource<<d08221cdf198c30256d8574839ecbf7a>>
  */
 
 'use strict';
@@ -145,7 +145,7 @@ var createRootStrictEffectsByDefault = false;
 var enableLazyContextPropagation = false;
 var enableLegacyHidden = false;
 var enableAsyncActions = false;
-var alwaysThrottleRetries = true; // Flow magic to verify the exports of this file match the original version.
+var alwaysThrottleRetries = true;
 
 var FunctionComponent = 0;
 var ClassComponent = 1;
@@ -23997,7 +23997,7 @@ function createFiberRoot(
   return root;
 }
 
-var ReactVersion = "18.3.0-canary-a6ed60a8e-20230929";
+var ReactVersion = "18.3.0-canary-54baa7997-20231002";
 
 // Might add PROFILE later.
 

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-prod.js

@@ -8623,7 +8623,7 @@ var devToolsConfig$jscomp$inline_1030 = {
     throw Error("TestRenderer does not support findFiberByHostInstance()");
   },
   bundleType: 0,
-  version: "18.3.0-canary-a6ed60a8e-20230929",
+  version: "18.3.0-canary-54baa7997-20231002",
   rendererPackageName: "react-test-renderer"
 };
 var internals$jscomp$inline_1229 = {
@@ -8654,7 +8654,7 @@ var internals$jscomp$inline_1229 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-a6ed60a8e-20230929"
+  reconcilerVersion: "18.3.0-canary-54baa7997-20231002"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1230 = __REACT_DEVTOOLS_GLOBAL_HOOK__;

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-profiling.js

@@ -9049,7 +9049,7 @@ var devToolsConfig$jscomp$inline_1072 = {
     throw Error("TestRenderer does not support findFiberByHostInstance()");
   },
   bundleType: 0,
-  version: "18.3.0-canary-a6ed60a8e-20230929",
+  version: "18.3.0-canary-54baa7997-20231002",
   rendererPackageName: "react-test-renderer"
 };
 var internals$jscomp$inline_1270 = {
@@ -9080,7 +9080,7 @@ var internals$jscomp$inline_1270 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-a6ed60a8e-20230929"
+  reconcilerVersion: "18.3.0-canary-54baa7997-20231002"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1271 = __REACT_DEVTOOLS_GLOBAL_HOOK__;

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-dev.js

@@ -27,7 +27,7 @@ if (
 }
           "use strict";
 
-var ReactVersion = "18.3.0-canary-a6ed60a8e-20230929";
+var ReactVersion = "18.3.0-canary-54baa7997-20231002";
 
 // ATTENTION
 // When adding new symbols to this file,

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-prod.js

@@ -616,4 +616,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactCurrentDispatcher.current.useTransition();
 };
-exports.version = "18.3.0-canary-a6ed60a8e-20230929";
+exports.version = "18.3.0-canary-54baa7997-20231002";

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-profiling.js

@@ -619,7 +619,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactCurrentDispatcher.current.useTransition();
 };
-exports.version = "18.3.0-canary-a6ed60a8e-20230929";
+exports.version = "18.3.0-canary-54baa7997-20231002";
 
           /* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
 if (

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/REVISION

@@ -1 +1 @@
-a6ed60a8eb0626e5f84d0bdbb62c0b61219150d3
+54baa7997c7b0bbd456460ead6e051655ea43790

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/implementations/ReactFabric-dev.fb.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<86fb5a18e030273bb12b79024c6073c2>>
+ * @generated SignedSource<<c7798d7e49297e588bffdcccc6aa6cb9>>
  */
 
 'use strict';
@@ -3178,7 +3178,9 @@ function dispatchEvent(target, topLevelType, nativeEvent) {
 var enableUseRefAccessWarning = dynamicFlags.enableUseRefAccessWarning,
   enableDeferRootSchedulingToMicrotask =
     dynamicFlags.enableDeferRootSchedulingToMicrotask,
-  alwaysThrottleRetries = dynamicFlags.alwaysThrottleRetries; // The rest of the flags are static for better dead code elimination.
+  alwaysThrottleRetries = dynamicFlags.alwaysThrottleRetries,
+  useMicrotasksForSchedulingInFabric =
+    dynamicFlags.useMicrotasksForSchedulingInFabric; // The rest of the flags are static for better dead code elimination.
 var enableSchedulingProfiler = true;
 var enableProfilerTimer = true;
 var enableProfilerCommitHooks = true;
@@ -5073,6 +5075,12 @@ function preloadInstance(type, props) {
 function waitForCommitToBeReady() {
   return null;
 }
+//     Microtasks
+// -------------------
+
+var supportsMicrotasks = useMicrotasksForSchedulingInFabric;
+var scheduleMicrotask =
+  typeof queueMicrotask === "function" ? queueMicrotask : scheduleTimeout;
 
 // This is ok in DOM because they types are interchangeable, but in React Native
 // they aren't.
@@ -10097,7 +10105,28 @@ function scheduleImmediateTask(cb) {
   } // TODO: Can we land supportsMicrotasks? Which environments don't support it?
   // Alternatively, can we move this check to the host config?
 
-  {
+  if (supportsMicrotasks) {
+    scheduleMicrotask(function () {
+      // In Safari, appending an iframe forces microtasks to run.
+      // https://github.com/facebook/react/issues/22459
+      // We don't support running callbacks in the middle of render
+      // or commit so we need to check against that.
+      var executionContext = getExecutionContext();
+
+      if ((executionContext & (RenderContext | CommitContext)) !== NoContext) {
+        // Note that this would still prematurely flush the callbacks
+        // if this happens outside render or commit phase (e.g. in an event).
+        // Intentionally using a macrotask instead of a microtask here. This is
+        // wrong semantically but it prevents an infinite loop. The bug is
+        // Safari's, not ours, so we just do our best to not crash even though
+        // the behavior isn't completely correct.
+        scheduleCallback$2(ImmediatePriority, cb);
+        return;
+      }
+
+      cb();
+    });
+  } else {
     // If microtasks are not supported, use Scheduler.
     scheduleCallback$2(ImmediatePriority, cb);
   }
@@ -27034,7 +27063,7 @@ function createFiberRoot(
   return root;
 }
 
-var ReactVersion = "18.3.0-canary-84876954";
+var ReactVersion = "18.3.0-canary-4227b2ef";
 
 function createPortal$1(
   children,

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/implementations/ReactFabric-prod.fb.js

@@ -7,14 +7,14 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<c369fd4070037f1dc7d616d80d10dcfd>>
+ * @generated SignedSource<<35a02eea4da4b468c9397d48533b560b>>
  */
 
 "use strict";
 require("react-native/Libraries/ReactPrivate/ReactNativePrivateInitializeCore");
 var ReactNativePrivateInterface = require("react-native/Libraries/ReactPrivate/ReactNativePrivateInterface"),
-  React = require("react"),
   dynamicFlags = require("ReactNativeInternalFeatureFlags"),
+  React = require("react"),
   Scheduler = require("scheduler");
 function invokeGuardedCallbackImpl(name, func, context) {
   var funcArgs = Array.prototype.slice.call(arguments, 3);
@@ -1318,6 +1318,8 @@ var enableUseRefAccessWarning = dynamicFlags.enableUseRefAccessWarning,
   enableDeferRootSchedulingToMicrotask =
     dynamicFlags.enableDeferRootSchedulingToMicrotask,
   alwaysThrottleRetries = dynamicFlags.alwaysThrottleRetries,
+  useMicrotasksForSchedulingInFabric =
+    dynamicFlags.useMicrotasksForSchedulingInFabric,
   scheduleCallback$2 = Scheduler.unstable_scheduleCallback,
   cancelCallback$1 = Scheduler.unstable_cancelCallback,
   shouldYield = Scheduler.unstable_shouldYield,
@@ -1627,6 +1629,8 @@ function cloneHiddenInstance(instance) {
     canonical: instance.canonical
   };
 }
+var scheduleMicrotask =
+  "function" === typeof queueMicrotask ? queueMicrotask : scheduleTimeout;
 function getInstanceFromNode(node) {
   return null != node.canonical && null != node.canonical.internalInstanceHandle
     ? node.canonical.internalInstanceHandle
@@ -3361,7 +3365,7 @@ function ensureRootIsScheduled(root) {
   mightHavePendingSyncWork = !0;
   didScheduleMicrotask ||
     ((didScheduleMicrotask = !0),
-    scheduleCallback$2(ImmediatePriority, processRootScheduleInMicrotask));
+    scheduleImmediateTask(processRootScheduleInMicrotask));
   enableDeferRootSchedulingToMicrotask ||
     scheduleTaskForRootDuringMicrotask(root, now());
 }
@@ -3446,8 +3450,7 @@ function flushSyncWorkAcrossRoots_impl(onlyLegacy) {
         if ("function" === typeof AggregateError)
           throw new AggregateError(errors);
         for (onlyLegacy = 1; onlyLegacy < errors.length; onlyLegacy++)
-          (didPerformSomeWork = throwError.bind(null, errors[onlyLegacy])),
-            scheduleCallback$2(ImmediatePriority, didPerformSomeWork);
+          scheduleImmediateTask(throwError.bind(null, errors[onlyLegacy]));
       }
       throw errors[0];
     }
@@ -3547,6 +3550,15 @@ function scheduleTaskForRootDuringMicrotask(root, currentTime) {
   root.callbackNode = suspendedLanes;
   return currentTime;
 }
+function scheduleImmediateTask(cb) {
+  useMicrotasksForSchedulingInFabric
+    ? scheduleMicrotask(function () {
+        0 !== (executionContext & 6)
+          ? scheduleCallback$2(ImmediatePriority, cb)
+          : cb();
+      })
+    : scheduleCallback$2(ImmediatePriority, cb);
+}
 var ReactCurrentDispatcher$1 = ReactSharedInternals.ReactCurrentDispatcher,
   ReactCurrentBatchConfig$2 = ReactSharedInternals.ReactCurrentBatchConfig,
   renderLanes$1 = 0,
@@ -9425,10 +9437,10 @@ batchedUpdatesImpl = function (fn, a) {
   }
 };
 var roots = new Map(),
-  devToolsConfig$jscomp$inline_1039 = {
+  devToolsConfig$jscomp$inline_1035 = {
     findFiberByHostInstance: getInstanceFromNode,
     bundleType: 0,
-    version: "18.3.0-canary-0ca674fe",
+    version: "18.3.0-canary-6367a5b9",
     rendererPackageName: "react-native-renderer",
     rendererConfig: {
       getInspectorDataForInstance: getInspectorDataForInstance,
@@ -9444,11 +9456,11 @@ var roots = new Map(),
       }.bind(null, findNodeHandle)
     }
   };
-var internals$jscomp$inline_1281 = {
-  bundleType: devToolsConfig$jscomp$inline_1039.bundleType,
-  version: devToolsConfig$jscomp$inline_1039.version,
-  rendererPackageName: devToolsConfig$jscomp$inline_1039.rendererPackageName,
-  rendererConfig: devToolsConfig$jscomp$inline_1039.rendererConfig,
+var internals$jscomp$inline_1277 = {
+  bundleType: devToolsConfig$jscomp$inline_1035.bundleType,
+  version: devToolsConfig$jscomp$inline_1035.version,
+  rendererPackageName: devToolsConfig$jscomp$inline_1035.rendererPackageName,
+  rendererConfig: devToolsConfig$jscomp$inline_1035.rendererConfig,
   overrideHookState: null,
   overrideHookStateDeletePath: null,
   overrideHookStateRenamePath: null,
@@ -9464,26 +9476,26 @@ var internals$jscomp$inline_1281 = {
     return null === fiber ? null : fiber.stateNode;
   },
   findFiberByHostInstance:
-    devToolsConfig$jscomp$inline_1039.findFiberByHostInstance ||
+    devToolsConfig$jscomp$inline_1035.findFiberByHostInstance ||
     emptyFindFiberByHostInstance,
   findHostInstancesForRefresh: null,
   scheduleRefresh: null,
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-0ca674fe"
+  reconcilerVersion: "18.3.0-canary-6367a5b9"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
-  var hook$jscomp$inline_1282 = __REACT_DEVTOOLS_GLOBAL_HOOK__;
+  var hook$jscomp$inline_1278 = __REACT_DEVTOOLS_GLOBAL_HOOK__;
   if (
-    !hook$jscomp$inline_1282.isDisabled &&
-    hook$jscomp$inline_1282.supportsFiber
+    !hook$jscomp$inline_1278.isDisabled &&
+    hook$jscomp$inline_1278.supportsFiber
   )
     try {
-      (rendererID = hook$jscomp$inline_1282.inject(
-        internals$jscomp$inline_1281
+      (rendererID = hook$jscomp$inline_1278.inject(
+        internals$jscomp$inline_1277
       )),
-        (injectedHook = hook$jscomp$inline_1282);
+        (injectedHook = hook$jscomp$inline_1278);
     } catch (err) {}
 }
 exports.createPortal = function (children, containerTag) {