Flow: typing of Scheduler (#25317)

Enables well formed exports for /scheduler. Some of the modules there were missing `@flow` and were therefore completely unchecked (despite some spurious types sprinkled around).

packages/scheduler/src/SchedulerFeatureFlags.js

@@ -4,6 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
+ * @flow strict
  */
 
 export const enableSchedulerDebugging = false;

packages/scheduler/src/SchedulerMinHeap.js

@@ -7,23 +7,24 @@
  * @flow strict
  */
 
-type Heap = Array<Node>;
+type Heap<T: Node> = Array<T>;
 type Node = {
   id: number,
   sortIndex: number,
+  ...
 };
 
-export function push(heap: Heap, node: Node): void {
+export function push<T: Node>(heap: Heap<T>, node: T): void {
   const index = heap.length;
   heap.push(node);
   siftUp(heap, node, index);
 }
 
-export function peek(heap: Heap): Node | null {
+export function peek<T: Node>(heap: Heap<T>): T | null {
   return heap.length === 0 ? null : heap[0];
 }
 
-export function pop(heap: Heap): Node | null {
+export function pop<T: Node>(heap: Heap<T>): T | null {
   if (heap.length === 0) {
     return null;
   }
@@ -36,7 +37,7 @@ export function pop(heap: Heap): Node | null {
   return first;
 }
 
-function siftUp(heap, node, i) {
+function siftUp<T: Node>(heap: Heap<T>, node: T, i: number): void {
   let index = i;
   while (index > 0) {
     const parentIndex = (index - 1) >>> 1;
@@ -53,7 +54,7 @@ function siftUp(heap, node, i) {
   }
 }
 
-function siftDown(heap, node, i) {
+function siftDown<T: Node>(heap: Heap<T>, node: T, i: number): void {
   let index = i;
   const length = heap.length;
   const halfLength = length >>> 1;
@@ -85,7 +86,7 @@ function siftDown(heap, node, i) {
   }
 }
 
-function compare(a, b) {
+function compare(a: Node, b: Node) {
   // Compare sort index first, then task id.
   const diff = a.sortIndex - b.sortIndex;
   return diff !== 0 ? diff : a.id - b.id;

packages/scheduler/src/SchedulerPriorities.js

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  */
 
 export type PriorityLevel = 0 | 1 | 2 | 3 | 4 | 5;

packages/scheduler/src/forks/Scheduler.js

@@ -4,10 +4,13 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
+ * @flow
  */
 
 /* eslint-disable no-var */
 
+import type {PriorityLevel} from '../SchedulerPriorities';
+
 import {
   enableSchedulerDebugging,
   enableProfiling,
@@ -41,7 +44,19 @@ import {
   startLoggingProfilingEvents,
 } from '../SchedulerProfiling';
 
-let getCurrentTime;
+export type Callback = boolean => ?Callback;
+
+type Task = {
+  id: number,
+  callback: Callback | null,
+  priorityLevel: PriorityLevel,
+  startTime: number,
+  expirationTime: number,
+  sortIndex: number,
+  isQueued?: boolean,
+};
+
+let getCurrentTime: () => number | DOMHighResTimeStamp;
 const hasPerformanceNow =
   typeof performance === 'object' && typeof performance.now === 'function';
 
@@ -96,7 +111,9 @@ const localSetImmediate =
 
 const isInputPending =
   typeof navigator !== 'undefined' &&
+  // $FlowFixMe[prop-missing]
   navigator.scheduling !== undefined &&
+  // $FlowFixMe[incompatible-type]
   navigator.scheduling.isInputPending !== undefined
     ? navigator.scheduling.isInputPending.bind(navigator.scheduling)
     : null;
@@ -247,7 +264,10 @@ function workLoop(hasTimeRemaining, initialTime) {
   }
 }
 
-function unstable_runWithPriority(priorityLevel, eventHandler) {
+function unstable_runWithPriority<T>(
+  priorityLevel: PriorityLevel,
+  eventHandler: () => T,
+): T {
   switch (priorityLevel) {
     case ImmediatePriority:
     case UserBlockingPriority:
@@ -269,7 +289,7 @@ function unstable_runWithPriority(priorityLevel, eventHandler) {
   }
 }
 
-function unstable_next(eventHandler) {
+function unstable_next<T>(eventHandler: () => T): T {
   var priorityLevel;
   switch (currentPriorityLevel) {
     case ImmediatePriority:
@@ -294,8 +314,9 @@ function unstable_next(eventHandler) {
   }
 }
 
-function unstable_wrapCallback(callback) {
+function unstable_wrapCallback<T: (...Array<mixed>) => mixed>(callback: T): T {
   var parentPriorityLevel = currentPriorityLevel;
+  // $FlowFixMe[incompatible-return]
   return function() {
     // This is a fork of runWithPriority, inlined for performance.
     var previousPriorityLevel = currentPriorityLevel;
@@ -309,7 +330,11 @@ function unstable_wrapCallback(callback) {
   };
 }
 
-function unstable_scheduleCallback(priorityLevel, callback, options) {
+function unstable_scheduleCallback(
+  priorityLevel: PriorityLevel,
+  callback: Callback,
+  options?: {delay: number},
+): Task {
   var currentTime = getCurrentTime();
 
   var startTime;
@@ -346,7 +371,7 @@ function unstable_scheduleCallback(priorityLevel, callback, options) {
 
   var expirationTime = startTime + timeout;
 
-  var newTask = {
+  var newTask: Task = {
     id: taskIdCounter++,
     callback,
     priorityLevel,
@@ -403,11 +428,11 @@ function unstable_continueExecution() {
   }
 }
 
-function unstable_getFirstCallbackNode() {
+function unstable_getFirstCallbackNode(): Task | null {
   return peek(taskQueue);
 }
 
-function unstable_cancelCallback(task) {
+function unstable_cancelCallback(task: Task) {
   if (enableProfiling) {
     if (task.isQueued) {
       const currentTime = getCurrentTime();
@@ -422,13 +447,18 @@ function unstable_cancelCallback(task) {
   task.callback = null;
 }
 
-function unstable_getCurrentPriorityLevel() {
+function unstable_getCurrentPriorityLevel(): PriorityLevel {
   return currentPriorityLevel;
 }
 
 let isMessageLoopRunning = false;
-let scheduledHostCallback = null;
-let taskTimeoutID = -1;
+let scheduledHostCallback:
+  | null
+  | ((
+      hasTimeRemaining: boolean,
+      initialTime: DOMHighResTimeStamp | number,
+    ) => boolean) = null;
+let taskTimeoutID: TimeoutID = (-1: any);
 
 // Scheduler periodically yields in case there is other work on the main
 // thread, like user events. By default, it yields multiple times per frame.
@@ -441,7 +471,7 @@ let startTime = -1;
 
 let needsPaint = false;
 
-function shouldYieldToHost() {
+function shouldYieldToHost(): boolean {
   const timeElapsed = getCurrentTime() - startTime;
   if (timeElapsed < frameInterval) {
     // The main thread has only been blocked for a really short amount of time;
@@ -490,7 +520,9 @@ function requestPaint() {
   if (
     enableIsInputPending &&
     navigator !== undefined &&
+    // $FlowFixMe[prop-missing]
     navigator.scheduling !== undefined &&
+    // $FlowFixMe[incompatible-type]
     navigator.scheduling.isInputPending !== undefined
   ) {
     needsPaint = true;
@@ -499,7 +531,7 @@ function requestPaint() {
   // Since we yield every frame regardless, `requestPaint` has no effect.
 }
 
-function forceFrameRate(fps) {
+function forceFrameRate(fps: number) {
   if (fps < 0 || fps > 125) {
     // Using console['error'] to evade Babel and ESLint
     console['error'](
@@ -579,6 +611,7 @@ if (typeof localSetImmediate === 'function') {
 } else {
   // We should only fallback here in non-browser environments.
   schedulePerformWorkUntilDeadline = () => {
+    // $FlowFixMe[not-a-function] nullable value
     localSetTimeout(performWorkUntilDeadline, 0);
   };
 }
@@ -592,14 +625,16 @@ function requestHostCallback(callback) {
 }
 
 function requestHostTimeout(callback, ms) {
+  // $FlowFixMe[not-a-function] nullable value
   taskTimeoutID = localSetTimeout(() => {
     callback(getCurrentTime());
   }, ms);
 }
 
 function cancelHostTimeout() {
+  // $FlowFixMe[not-a-function] nullable value
   localClearTimeout(taskTimeoutID);
-  taskTimeoutID = -1;
+  taskTimeoutID = ((-1: any): TimeoutID);
 }
 
 export {
@@ -623,7 +658,10 @@ export {
   forceFrameRate as unstable_forceFrameRate,
 };
 
-export const unstable_Profiling = enableProfiling
+export const unstable_Profiling: {
+  startLoggingProfilingEvents(): void,
+  stopLoggingProfilingEvents(): ArrayBuffer | null,
+} | null = enableProfiling
   ? {
       startLoggingProfilingEvents,
       stopLoggingProfilingEvents,

packages/scheduler/src/forks/SchedulerFeatureFlags.www-dynamic.js

@@ -3,7 +3,6 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
- *
  */
 
 // In www, these flags are controlled by GKs. Because most GKs have some

packages/scheduler/src/forks/SchedulerFeatureFlags.www.js

@@ -4,8 +4,10 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
+ * @flow
  */
 
+// $FlowFixMe[cannot-resolve-module]
 const dynamicFeatureFlags = require('SchedulerFeatureFlags');
 
 // Re-export dynamic flags from the www version.
@@ -19,4 +21,5 @@ export const {
   maxYieldMs,
 } = dynamicFeatureFlags;
 
-export const enableProfiling = __PROFILE__ && enableProfilingFeatureFlag;
+export const enableProfiling: boolean =
+  __PROFILE__ && enableProfilingFeatureFlag;