Move sync task queue to its own module (#21109)

The sync task queue is React-specific and doesn't really have anything
to do with Scheduler. We'd keep using it even once `postTask` exists.

By separating that part out, `SchedulerWithReactIntegration` is now
just a module that re-exports the Scheduler API. So I unforked it.
When we switch to ES Modules, we can remove this re-exporting module.

packages/react-dom/src/events/ReactDOMEventListener.js

@@ -34,25 +34,21 @@ import {
 import getEventTarget from './getEventTarget';
 import {getClosestInstanceFromNode} from '../client/ReactDOMComponentTree';
 
-import {
-  enableLegacyFBSupport,
-  enableNewReconciler,
-} from 'shared/ReactFeatureFlags';
+import {enableLegacyFBSupport} from 'shared/ReactFeatureFlags';
 import {dispatchEventForPluginEventSystem} from './DOMPluginEventSystem';
 import {
   flushDiscreteUpdatesIfNeeded,
   discreteUpdates,
 } from './ReactDOMUpdateBatching';
 
-import {getCurrentPriorityLevel as getCurrentPriorityLevel_old} from 'react-reconciler/src/SchedulerWithReactIntegration.old';
 import {
-  getCurrentPriorityLevel as getCurrentPriorityLevel_new,
+  getCurrentPriorityLevel as getCurrentSchedulerPriorityLevel,
   IdlePriority as IdleSchedulerPriority,
   ImmediatePriority as ImmediateSchedulerPriority,
   LowPriority as LowSchedulerPriority,
   NormalPriority as NormalSchedulerPriority,
   UserBlockingPriority as UserBlockingSchedulerPriority,
-} from 'react-reconciler/src/SchedulerWithReactIntegration.new';
+} from 'react-reconciler/src/Scheduler';
 import {
   DiscreteEventPriority,
   ContinuousEventPriority,
@@ -62,10 +58,6 @@ import {
   setCurrentUpdatePriority,
 } from 'react-reconciler/src/ReactEventPriorities';
 
-const getCurrentPriorityLevel = enableNewReconciler
-  ? getCurrentPriorityLevel_new
-  : getCurrentPriorityLevel_old;
-
 // TODO: can we stop exporting these?
 export let _enabled = true;
 
@@ -392,7 +384,7 @@ export function getEventPriority(domEventName: DOMEventName): * {
       // We might be in the Scheduler callback.
       // Eventually this mechanism will be replaced by a check
       // of the current priority on the native scheduler.
-      const schedulerPriority = getCurrentPriorityLevel();
+      const schedulerPriority = getCurrentSchedulerPriorityLevel();
       switch (schedulerPriority) {
         case ImmediateSchedulerPriority:
           return DiscreteEventPriority;

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

@@ -28,7 +28,7 @@ import type {Cache, SpawnedCachePool} from './ReactFiberCacheComponent.new';
 
 import {resetWorkInProgressVersions as resetMutableSourceWorkInProgressVersions} from './ReactMutableSource.new';
 
-import {now} from './SchedulerWithReactIntegration.new';
+import {now} from './Scheduler';
 
 import {
   IndeterminateComponent,

packages/react-reconciler/src/ReactFiberCompleteWork.old.js

@@ -28,7 +28,7 @@ import type {Cache, SpawnedCachePool} from './ReactFiberCacheComponent.old';
 
 import {resetWorkInProgressVersions as resetMutableSourceWorkInProgressVersions} from './ReactMutableSource.old';
 
-import {now} from './SchedulerWithReactIntegration.old';
+import {now} from './Scheduler';
 
 import {
   IndeterminateComponent,

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

@@ -25,7 +25,7 @@ import {
   UserBlockingPriority as UserBlockingSchedulerPriority,
   NormalPriority as NormalSchedulerPriority,
   IdlePriority as IdleSchedulerPriority,
-} from './SchedulerWithReactIntegration.new';
+} from './Scheduler';
 
 declare var __REACT_DEVTOOLS_GLOBAL_HOOK__: Object | void;
 

packages/react-reconciler/src/ReactFiberDevToolsHook.old.js

@@ -25,7 +25,7 @@ import {
   UserBlockingPriority as UserBlockingSchedulerPriority,
   NormalPriority as NormalSchedulerPriority,
   IdlePriority as IdleSchedulerPriority,
-} from './SchedulerWithReactIntegration.old';
+} from './Scheduler';
 
 declare var __REACT_DEVTOOLS_GLOBAL_HOOK__: Object | void;
 

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

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import type {SchedulerCallback} from './Scheduler';
+
+import {
+  DiscreteEventPriority,
+  getCurrentUpdatePriority,
+  setCurrentUpdatePriority,
+} from './ReactEventPriorities.new';
+import {ImmediatePriority, scheduleCallback} from './Scheduler';
+
+let syncQueue: Array<SchedulerCallback> | null = null;
+let isFlushingSyncQueue: boolean = false;
+
+export function scheduleSyncCallback(callback: SchedulerCallback) {
+  // Push this callback into an internal queue. We'll flush these either in
+  // the next tick, or earlier if something calls `flushSyncCallbackQueue`.
+  if (syncQueue === null) {
+    syncQueue = [callback];
+  } else {
+    // Push onto existing queue. Don't need to schedule a callback because
+    // we already scheduled one when we created the queue.
+    syncQueue.push(callback);
+  }
+}
+
+export function flushSyncCallbackQueue() {
+  if (!isFlushingSyncQueue && syncQueue !== null) {
+    // Prevent re-entrancy.
+    isFlushingSyncQueue = true;
+    let i = 0;
+    const previousUpdatePriority = getCurrentUpdatePriority();
+    try {
+      const isSync = true;
+      const queue = syncQueue;
+      // TODO: Is this necessary anymore? The only user code that runs in this
+      // queue is in the render or commit phases.
+      setCurrentUpdatePriority(DiscreteEventPriority);
+      for (; i < queue.length; i++) {
+        let callback = queue[i];
+        do {
+          callback = callback(isSync);
+        } while (callback !== null);
+      }
+      syncQueue = null;
+    } 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
+      scheduleCallback(ImmediatePriority, flushSyncCallbackQueue);
+      throw error;
+    } finally {
+      setCurrentUpdatePriority(previousUpdatePriority);
+      isFlushingSyncQueue = false;
+    }
+  }
+  return null;
+}

packages/react-reconciler/src/ReactFiberSyncTaskQueue.old.js

@@ -7,50 +7,15 @@
  * @flow
  */
 
-// This module only exists as an ESM wrapper around the external CommonJS
-// Scheduler dependency. Notice that we're intentionally not using named imports
-// because Rollup would use dynamic dispatch for CommonJS interop named imports.
-// When we switch to ESM, we can delete this module.
-import * as Scheduler from 'scheduler';
-import {__interactionsRef} from 'scheduler/tracing';
-import {enableSchedulerTracing} from 'shared/ReactFeatureFlags';
-import invariant from 'shared/invariant';
+import type {SchedulerCallback} from './Scheduler';
+
 import {
   DiscreteEventPriority,
   getCurrentUpdatePriority,
   setCurrentUpdatePriority,
 } from './ReactEventPriorities.old';
+import {ImmediatePriority, scheduleCallback} from './Scheduler';
 
-export const scheduleCallback = Scheduler.unstable_scheduleCallback;
-export const cancelCallback = Scheduler.unstable_cancelCallback;
-export const shouldYield = Scheduler.unstable_shouldYield;
-export const requestPaint = Scheduler.unstable_requestPaint;
-export const now = Scheduler.unstable_now;
-export const getCurrentPriorityLevel =
-  Scheduler.unstable_getCurrentPriorityLevel;
-export const ImmediatePriority = Scheduler.unstable_ImmediatePriority;
-export const UserBlockingPriority = Scheduler.unstable_UserBlockingPriority;
-export const NormalPriority = Scheduler.unstable_NormalPriority;
-export const LowPriority = Scheduler.unstable_LowPriority;
-export const IdlePriority = Scheduler.unstable_IdlePriority;
-
-if (enableSchedulerTracing) {
-  // Provide explicit error message when production+profiling bundle of e.g.
-  // react-dom is used with production (non-profiling) bundle of
-  // scheduler/tracing
-  invariant(
-    __interactionsRef != null && __interactionsRef.current != null,
-    'It is not supported to run the profiling version of a renderer (for ' +
-      'example, `react-dom/profiling`) without also replacing the ' +
-      '`scheduler/tracing` module with `scheduler/tracing-profiling`. Your ' +
-      'bundler might have a setting for aliasing both modules. Learn more at ' +
-      'https://reactjs.org/link/profiling',
-  );
-}
-
-export type SchedulerCallback = (isSync: boolean) => SchedulerCallback | null;
-
-// TODO: Move sync task queue to its own module.
 let syncQueue: Array<SchedulerCallback> | null = null;
 let isFlushingSyncQueue: boolean = false;
 

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

@@ -46,9 +46,11 @@ import {
   UserBlockingPriority as UserBlockingSchedulerPriority,
   NormalPriority as NormalSchedulerPriority,
   IdlePriority as IdleSchedulerPriority,
+} from './Scheduler';
+import {
   flushSyncCallbackQueue,
   scheduleSyncCallback,
-} from './SchedulerWithReactIntegration.new';
+} from './ReactFiberSyncTaskQueue.new';
 import {
   NoFlags as NoHookEffect,
   Passive as HookPassive,

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

@@ -46,9 +46,11 @@ import {
   UserBlockingPriority as UserBlockingSchedulerPriority,
   NormalPriority as NormalSchedulerPriority,
   IdlePriority as IdleSchedulerPriority,
+} from './Scheduler';
+import {
   flushSyncCallbackQueue,
   scheduleSyncCallback,
-} from './SchedulerWithReactIntegration.old';
+} from './ReactFiberSyncTaskQueue.old';
 import {
   NoFlags as NoHookEffect,
   Passive as HookPassive,

packages/react-reconciler/src/Scheduler.js

@@ -15,11 +15,6 @@ import * as Scheduler from 'scheduler';
 import {__interactionsRef} from 'scheduler/tracing';
 import {enableSchedulerTracing} from 'shared/ReactFeatureFlags';
 import invariant from 'shared/invariant';
-import {
-  DiscreteEventPriority,
-  getCurrentUpdatePriority,
-  setCurrentUpdatePriority,
-} from './ReactEventPriorities.new';
 
 export const scheduleCallback = Scheduler.unstable_scheduleCallback;
 export const cancelCallback = Scheduler.unstable_cancelCallback;
@@ -49,54 +44,3 @@ if (enableSchedulerTracing) {
 }
 
 export type SchedulerCallback = (isSync: boolean) => SchedulerCallback | null;
-
-// TODO: Move sync task queue to its own module.
-let syncQueue: Array<SchedulerCallback> | null = null;
-let isFlushingSyncQueue: boolean = false;
-
-export function scheduleSyncCallback(callback: SchedulerCallback) {
-  // Push this callback into an internal queue. We'll flush these either in
-  // the next tick, or earlier if something calls `flushSyncCallbackQueue`.
-  if (syncQueue === null) {
-    syncQueue = [callback];
-  } else {
-    // Push onto existing queue. Don't need to schedule a callback because
-    // we already scheduled one when we created the queue.
-    syncQueue.push(callback);
-  }
-}
-
-export function flushSyncCallbackQueue() {
-  if (!isFlushingSyncQueue && syncQueue !== null) {
-    // Prevent re-entrancy.
-    isFlushingSyncQueue = true;
-    let i = 0;
-    const previousUpdatePriority = getCurrentUpdatePriority();
-    try {
-      const isSync = true;
-      const queue = syncQueue;
-      // TODO: Is this necessary anymore? The only user code that runs in this
-      // queue is in the render or commit phases.
-      setCurrentUpdatePriority(DiscreteEventPriority);
-      for (; i < queue.length; i++) {
-        let callback = queue[i];
-        do {
-          callback = callback(isSync);
-        } while (callback !== null);
-      }
-      syncQueue = null;
-    } 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
-      scheduleCallback(ImmediatePriority, flushSyncCallbackQueue);
-      throw error;
-    } finally {
-      setCurrentUpdatePriority(previousUpdatePriority);
-      isFlushingSyncQueue = false;
-    }
-  }
-  return null;
-}