[WIP] Add enableSyncDefaultUpdates

packages/react-reconciler/src/ReactFiberLane.new.js

@@ -36,7 +36,11 @@ export type Lane = number;
 export type LaneMap<T> = Array<T>;
 
 import invariant from 'shared/invariant';
-import {enableCache, enableSchedulingProfiler} from 'shared/ReactFeatureFlags';
+import {
+  enableCache,
+  enableSchedulingProfiler,
+  enableSyncDefaultUpdates,
+} from 'shared/ReactFeatureFlags';
 
 import {
   ImmediatePriority as ImmediateSchedulerPriority,
@@ -539,6 +543,9 @@ export function findUpdateLane(lanePriority: LanePriority): Lane {
     case SyncLanePriority:
       return SyncLane;
     case InputContinuousLanePriority:
+      if (enableSyncDefaultUpdates) {
+        return DefaultLanePriority;
+      }
       return InputContinuousLane;
     case DefaultLanePriority:
       return DefaultLane;

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

@@ -32,6 +32,7 @@ import {
   disableSchedulerTimeoutInWorkLoop,
   enableStrictEffects,
   skipUnmountedBoundaries,
+  enableSyncDefaultUpdates,
 } from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import invariant from 'shared/invariant';
@@ -681,7 +682,12 @@ function ensureRootIsScheduled(root: FiberRoot, currentTime: number) {
 
   // Schedule a new callback.
   let newCallbackNode;
-  if (newCallbackPriority === SyncLanePriority) {
+  if (enableSyncDefaultUpdates && newCallbackPriority === DefaultLanePriority) {
+    newCallbackNode = scheduleCallback(
+      ImmediateSchedulerPriority,
+      performSyncWorkOnRoot.bind(null, root),
+    );
+  } else if (newCallbackPriority === SyncLanePriority) {
     // Special case: Sync React callbacks are scheduled on a special
     // internal queue
     scheduleSyncCallback(performSyncWorkOnRoot.bind(null, root));

packages/shared/ReactFeatureFlags.js

@@ -164,3 +164,5 @@ export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableLazyContextPropagation = false;
+
+export const enableSyncDefaultUpdates = false;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -59,6 +59,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -58,6 +58,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -58,6 +58,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.test-renderer.native.js

@@ -58,6 +58,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -58,6 +58,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.testing.js

@@ -58,6 +58,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.testing.www.js

@@ -58,6 +58,7 @@ export const enableUseRefAccessWarning = false;
 export const enableRecursiveCommitTraversal = false;
 export const disableSchedulerTimeoutInWorkLoop = false;
 export const enableLazyContextPropagation = false;
+export const enableSyncDefaultUpdates = false;
 
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars

packages/shared/forks/ReactFeatureFlags.www-dynamic.js

@@ -57,3 +57,4 @@ export const deletedTreeCleanUpLevel = __VARIANT__ ? 3 : 1;
 export const enableProfilerNestedUpdateScheduledHook = __VARIANT__;
 export const disableSchedulerTimeoutInWorkLoop = __VARIANT__;
 export const enableLazyContextPropagation = __VARIANT__;
+export const enableSyncDefaultUpdates = __VARIANT__;

packages/shared/forks/ReactFeatureFlags.www.js

@@ -92,6 +92,9 @@ export const enableNewReconciler = __VARIANT__;
 
 export const enableRecursiveCommitTraversal = false;
 
+// WWW is on the new sync behavior by default unless overridden by roots.
+export const enableSyncDefaultUpdates = __VARIANT__;
+
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;