From 16443f78934e9f2162656750791cc62e0d120035 Mon Sep 17 00:00:00 2001
From: Andrew Clark <git@andrewclark.io>
Date: Fri, 18 Jan 2019 17:38:14 -0800
Subject: [PATCH] Add Scheduler.unstable_next

---
 packages/react/src/ReactSharedInternals.js    |  2 ++
 .../npm/umd/scheduler.development.js          |  8 +++++
 .../npm/umd/scheduler.production.min.js       |  8 +++++
 .../npm/umd/scheduler.profiling.min.js        |  8 +++++
 packages/scheduler/src/Scheduler.js           | 32 +++++++++++++++++++
 5 files changed, 58 insertions(+)

diff --git a/packages/react/src/ReactSharedInternals.js b/packages/react/src/ReactSharedInternals.js
index 9cdce1891bc5c..1fe0c2391bd13 100644
--- a/packages/react/src/ReactSharedInternals.js
+++ b/packages/react/src/ReactSharedInternals.js
@@ -12,6 +12,7 @@ import {
   unstable_now,
   unstable_scheduleCallback,
   unstable_runWithPriority,
+  unstable_next,
   unstable_getFirstCallbackNode,
   unstable_pauseExecution,
   unstable_continueExecution,
@@ -53,6 +54,7 @@ if (__UMD__) {
       unstable_now,
       unstable_scheduleCallback,
       unstable_runWithPriority,
+      unstable_next,
       unstable_wrapCallback,
       unstable_getFirstCallbackNode,
       unstable_pauseExecution,
diff --git a/packages/scheduler/npm/umd/scheduler.development.js b/packages/scheduler/npm/umd/scheduler.development.js
index 41ac8e437bbd6..ac632eb288bff 100644
--- a/packages/scheduler/npm/umd/scheduler.development.js
+++ b/packages/scheduler/npm/umd/scheduler.development.js
@@ -54,6 +54,13 @@
     );
   }
 
+  function unstable_next() {
+    return global.React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Scheduler.unstable_next.apply(
+      this,
+      arguments
+    );
+  }
+
   function unstable_wrapCallback() {
     return global.React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Scheduler.unstable_wrapCallback.apply(
       this,
@@ -95,6 +102,7 @@
     unstable_cancelCallback: unstable_cancelCallback,
     unstable_shouldYield: unstable_shouldYield,
     unstable_runWithPriority: unstable_runWithPriority,
+    unstable_next: unstable_next,
     unstable_wrapCallback: unstable_wrapCallback,
     unstable_getCurrentPriorityLevel: unstable_getCurrentPriorityLevel,
     unstable_continueExecution: unstable_continueExecution,
diff --git a/packages/scheduler/npm/umd/scheduler.production.min.js b/packages/scheduler/npm/umd/scheduler.production.min.js
index cea54f4da3cba..da2aefa9e4bf1 100644
--- a/packages/scheduler/npm/umd/scheduler.production.min.js
+++ b/packages/scheduler/npm/umd/scheduler.production.min.js
@@ -54,6 +54,13 @@
     );
   }
 
+  function unstable_next() {
+    return global.React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Scheduler.unstable_next.apply(
+      this,
+      arguments
+    );
+  }
+
   function unstable_wrapCallback() {
     return global.React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Scheduler.unstable_wrapCallback.apply(
       this,
@@ -89,6 +96,7 @@
     unstable_cancelCallback: unstable_cancelCallback,
     unstable_shouldYield: unstable_shouldYield,
     unstable_runWithPriority: unstable_runWithPriority,
+    unstable_next: unstable_next,
     unstable_wrapCallback: unstable_wrapCallback,
     unstable_getCurrentPriorityLevel: unstable_getCurrentPriorityLevel,
     unstable_continueExecution: unstable_continueExecution,
diff --git a/packages/scheduler/npm/umd/scheduler.profiling.min.js b/packages/scheduler/npm/umd/scheduler.profiling.min.js
index cea54f4da3cba..da2aefa9e4bf1 100644
--- a/packages/scheduler/npm/umd/scheduler.profiling.min.js
+++ b/packages/scheduler/npm/umd/scheduler.profiling.min.js
@@ -54,6 +54,13 @@
     );
   }
 
+  function unstable_next() {
+    return global.React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Scheduler.unstable_next.apply(
+      this,
+      arguments
+    );
+  }
+
   function unstable_wrapCallback() {
     return global.React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Scheduler.unstable_wrapCallback.apply(
       this,
@@ -89,6 +96,7 @@
     unstable_cancelCallback: unstable_cancelCallback,
     unstable_shouldYield: unstable_shouldYield,
     unstable_runWithPriority: unstable_runWithPriority,
+    unstable_next: unstable_next,
     unstable_wrapCallback: unstable_wrapCallback,
     unstable_getCurrentPriorityLevel: unstable_getCurrentPriorityLevel,
     unstable_continueExecution: unstable_continueExecution,
diff --git a/packages/scheduler/src/Scheduler.js b/packages/scheduler/src/Scheduler.js
index a6e27850dab71..df1e9b3bdada0 100644
--- a/packages/scheduler/src/Scheduler.js
+++ b/packages/scheduler/src/Scheduler.js
@@ -264,6 +264,37 @@ function unstable_runWithPriority(priorityLevel, eventHandler) {
   }
 }
 
+function unstable_next(eventHandler) {
+  let priorityLevel;
+  switch (currentPriorityLevel) {
+    case ImmediatePriority:
+    case UserBlockingPriority:
+    case NormalPriority:
+      // Shift down to normal priority
+      priorityLevel = NormalPriority;
+      break;
+    default:
+      // Anything lower than normal priority should remain at the current level.
+      priorityLevel = currentPriorityLevel;
+      break;
+  }
+
+  var previousPriorityLevel = currentPriorityLevel;
+  var previousEventStartTime = currentEventStartTime;
+  currentPriorityLevel = priorityLevel;
+  currentEventStartTime = getCurrentTime();
+
+  try {
+    return eventHandler();
+  } finally {
+    currentPriorityLevel = previousPriorityLevel;
+    currentEventStartTime = previousEventStartTime;
+
+    // Before exiting, flush all the immediate work that was scheduled.
+    flushImmediateWork();
+  }
+}
+
 function unstable_wrapCallback(callback) {
   var parentPriorityLevel = currentPriorityLevel;
   return function() {
@@ -688,6 +719,7 @@ export {
   IdlePriority as unstable_IdlePriority,
   LowPriority as unstable_LowPriority,
   unstable_runWithPriority,
+  unstable_next,
   unstable_scheduleCallback,
   unstable_cancelCallback,
   unstable_wrapCallback,