flushSync: Exhaust queue even if something throws (#26366)

If something throws as a result of `flushSync`, and there's remaining
work left in the queue, React should keep working until all the work is
complete.

If multiple errors are thrown, React will combine them into an
AggregateError object and throw that. In environments where
AggregateError is not available, React will rethrow in an async task.
(All the evergreen runtimes support AggregateError.)

The scenario where this happens is relatively rare, because `flushSync`
will only throw if there's no error boundary to capture the error.

DiffTrain build for [93c10df](93c10df)

compiled/facebook-www/REVISION

@@ -1 +1 @@
-ef8bdbecb6dbb9743b895c2e867e5a5264dd6651
+93c10dfa6b0848c12189b773b59c77d74cad2a1a

compiled/facebook-www/React-dev.modern.js

@@ -27,7 +27,7 @@ if (
 }
           "use strict";
 
-var ReactVersion = "18.3.0-www-modern-fd5743d3";
+var ReactVersion = "18.3.0-www-modern-f87ae691";
 
 // ATTENTION
 // When adding new symbols to this file,

compiled/facebook-www/ReactART-dev.classic.js

@@ -69,7 +69,7 @@ function _assertThisInitialized(self) {
   return self;
 }
 
-var ReactVersion = "18.3.0-www-classic-9d9aef36";
+var ReactVersion = "18.3.0-www-classic-600fa423";
 
 var LegacyRoot = 0;
 var ConcurrentRoot = 1;
@@ -3652,46 +3652,71 @@ function flushSyncCallbacksOnlyInLegacyMode() {
 function flushSyncCallbacks() {
   if (!isFlushingSyncQueue && syncQueue !== null) {
     // Prevent re-entrance.
-    isFlushingSyncQueue = true;
-    var i = 0;
-    var previousUpdatePriority = getCurrentUpdatePriority();
-
-    try {
-      var isSync = true;
-      var queue = syncQueue; // TODO: Is this necessary anymore? The only user code that runs in this
-      // queue is in the render or commit phases.
+    isFlushingSyncQueue = true; // Set the event priority to discrete
+    // TODO: Is this necessary anymore? The only user code that runs in this
+    // queue is in the render or commit phases, which already set the
+    // event priority. Should be able to remove.
 
-      setCurrentUpdatePriority(DiscreteEventPriority); // $FlowFixMe[incompatible-use] found when upgrading Flow
+    var previousUpdatePriority = getCurrentUpdatePriority();
+    setCurrentUpdatePriority(DiscreteEventPriority);
+    var errors = null;
+    var queue = syncQueue; // $FlowFixMe[incompatible-use] found when upgrading Flow
 
-      for (; i < queue.length; i++) {
-        // $FlowFixMe[incompatible-use] found when upgrading Flow
-        var callback = queue[i];
+    for (var i = 0; i < queue.length; i++) {
+      // $FlowFixMe[incompatible-use] found when upgrading Flow
+      var callback = queue[i];
 
+      try {
         do {
-          // $FlowFixMe[incompatible-type] we bail out when we get a null
+          var isSync = true; // $FlowFixMe[incompatible-type] we bail out when we get a null
+
           callback = callback(isSync);
         } while (callback !== null);
+      } catch (error) {
+        // Collect errors so we can rethrow them at the end
+        if (errors === null) {
+          errors = [error];
+        } else {
+          errors.push(error);
+        }
       }
+    }
 
-      syncQueue = null;
-      includesLegacySyncCallbacks = false;
-    } catch (error) {
-      // If something throws, leave the remaining callbacks on the queue.
-      if (syncQueue !== null) {
-        syncQueue = syncQueue.slice(i + 1);
-      } // Resume flushing in the next tick
+    syncQueue = null;
+    includesLegacySyncCallbacks = false;
+    setCurrentUpdatePriority(previousUpdatePriority);
+    isFlushingSyncQueue = false;
 
-      scheduleCallback$2(ImmediatePriority, flushSyncCallbacks);
-      throw error;
-    } finally {
-      setCurrentUpdatePriority(previousUpdatePriority);
-      isFlushingSyncQueue = false;
+    if (errors !== null) {
+      if (errors.length > 1) {
+        if (typeof AggregateError === "function") {
+          // eslint-disable-next-line no-undef
+          throw new AggregateError(errors);
+        } else {
+          for (var _i = 1; _i < errors.length; _i++) {
+            scheduleCallback$2(
+              ImmediatePriority,
+              throwError.bind(null, errors[_i])
+            );
+          }
+
+          var firstError = errors[0];
+          throw firstError;
+        }
+      } else {
+        var error = errors[0];
+        throw error;
+      }
     }
   }
 
   return null;
 }
 
+function throwError(error) {
+  throw error;
+}
+
 var nativeConsole = console;
 var nativeConsoleLog = null;
 var pendingGroupArgs = [];

compiled/facebook-www/ReactART-dev.modern.js

@@ -69,7 +69,7 @@ function _assertThisInitialized(self) {
   return self;
 }
 
-var ReactVersion = "18.3.0-www-modern-9e979f3e";
+var ReactVersion = "18.3.0-www-modern-ecb0bb1c";
 
 var LegacyRoot = 0;
 var ConcurrentRoot = 1;
@@ -3408,46 +3408,71 @@ function flushSyncCallbacksOnlyInLegacyMode() {
 function flushSyncCallbacks() {
   if (!isFlushingSyncQueue && syncQueue !== null) {
     // Prevent re-entrance.
-    isFlushingSyncQueue = true;
-    var i = 0;
-    var previousUpdatePriority = getCurrentUpdatePriority();
-
-    try {
-      var isSync = true;
-      var queue = syncQueue; // TODO: Is this necessary anymore? The only user code that runs in this
-      // queue is in the render or commit phases.
+    isFlushingSyncQueue = true; // Set the event priority to discrete
+    // TODO: Is this necessary anymore? The only user code that runs in this
+    // queue is in the render or commit phases, which already set the
+    // event priority. Should be able to remove.
 
-      setCurrentUpdatePriority(DiscreteEventPriority); // $FlowFixMe[incompatible-use] found when upgrading Flow
+    var previousUpdatePriority = getCurrentUpdatePriority();
+    setCurrentUpdatePriority(DiscreteEventPriority);
+    var errors = null;
+    var queue = syncQueue; // $FlowFixMe[incompatible-use] found when upgrading Flow
 
-      for (; i < queue.length; i++) {
-        // $FlowFixMe[incompatible-use] found when upgrading Flow
-        var callback = queue[i];
+    for (var i = 0; i < queue.length; i++) {
+      // $FlowFixMe[incompatible-use] found when upgrading Flow
+      var callback = queue[i];
 
+      try {
         do {
-          // $FlowFixMe[incompatible-type] we bail out when we get a null
+          var isSync = true; // $FlowFixMe[incompatible-type] we bail out when we get a null
+
           callback = callback(isSync);
         } while (callback !== null);
+      } catch (error) {
+        // Collect errors so we can rethrow them at the end
+        if (errors === null) {
+          errors = [error];
+        } else {
+          errors.push(error);
+        }
       }
+    }
 
-      syncQueue = null;
-      includesLegacySyncCallbacks = false;
-    } catch (error) {
-      // If something throws, leave the remaining callbacks on the queue.
-      if (syncQueue !== null) {
-        syncQueue = syncQueue.slice(i + 1);
-      } // Resume flushing in the next tick
+    syncQueue = null;
+    includesLegacySyncCallbacks = false;
+    setCurrentUpdatePriority(previousUpdatePriority);
+    isFlushingSyncQueue = false;
 
-      scheduleCallback$2(ImmediatePriority, flushSyncCallbacks);
-      throw error;
-    } finally {
-      setCurrentUpdatePriority(previousUpdatePriority);
-      isFlushingSyncQueue = false;
+    if (errors !== null) {
+      if (errors.length > 1) {
+        if (typeof AggregateError === "function") {
+          // eslint-disable-next-line no-undef
+          throw new AggregateError(errors);
+        } else {
+          for (var _i = 1; _i < errors.length; _i++) {
+            scheduleCallback$2(
+              ImmediatePriority,
+              throwError.bind(null, errors[_i])
+            );
+          }
+
+          var firstError = errors[0];
+          throw firstError;
+        }
+      } else {
+        var error = errors[0];
+        throw error;
+      }
     }
   }
 
   return null;
 }
 
+function throwError(error) {
+  throw error;
+}
+
 var nativeConsole = console;
 var nativeConsoleLog = null;
 var pendingGroupArgs = [];