From 79eafd877ac826eafed75eaefb1d236a9ec0305b Mon Sep 17 00:00:00 2001
From: Rick Hanlon <rickhanlonii@gmail.com>
Date: Tue, 2 Mar 2021 16:53:50 -0700
Subject: [PATCH] Use update lane priority to set pending updates on roots

---
 .../src/ReactFiberWorkLoop.new.js             | 21 +++++++++++++++++++
 .../src/ReactFiberWorkLoop.old.js             | 21 +++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.new.js b/packages/react-reconciler/src/ReactFiberWorkLoop.new.js
index b404837cb25d0..08c12bf821978 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.new.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.new.js
@@ -597,6 +597,27 @@ export function scheduleUpdateOnFiber(
         flushSyncCallbackQueue();
       }
     }
+  } else if (decoupleUpdatePriorityFromScheduler) {
+    const updateLanePriority = getCurrentUpdateLanePriority();
+
+    // Schedule a discrete update but only if it's not Sync.
+    if (
+      (executionContext & DiscreteEventContext) !== NoContext &&
+      // Only updates at user-blocking priority or greater are considered
+      // discrete, even inside a discrete event.
+      updateLanePriority === InputDiscreteLanePriority
+    ) {
+      // This is the result of a discrete event. Track the lowest priority
+      // discrete update per root so we can flush them early, if needed.
+      if (rootsWithPendingDiscreteUpdates === null) {
+        rootsWithPendingDiscreteUpdates = new Set([root]);
+      } else {
+        rootsWithPendingDiscreteUpdates.add(root);
+      }
+    }
+    // Schedule other updates after in case the callback is sync.
+    ensureRootIsScheduled(root, eventTime);
+    schedulePendingInteractions(root, lane);
   } else {
     // Schedule a discrete update but only if it's not Sync.
     if (
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.old.js b/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
index 0a366eece7321..566874ca705b6 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
@@ -597,6 +597,27 @@ export function scheduleUpdateOnFiber(
         flushSyncCallbackQueue();
       }
     }
+  } else if (decoupleUpdatePriorityFromScheduler) {
+    const updateLanePriority = getCurrentUpdateLanePriority();
+
+    // Schedule a discrete update but only if it's not Sync.
+    if (
+      (executionContext & DiscreteEventContext) !== NoContext &&
+      // Only updates at user-blocking priority or greater are considered
+      // discrete, even inside a discrete event.
+      updateLanePriority === InputDiscreteLanePriority
+    ) {
+      // This is the result of a discrete event. Track the lowest priority
+      // discrete update per root so we can flush them early, if needed.
+      if (rootsWithPendingDiscreteUpdates === null) {
+        rootsWithPendingDiscreteUpdates = new Set([root]);
+      } else {
+        rootsWithPendingDiscreteUpdates.add(root);
+      }
+    }
+    // Schedule other updates after in case the callback is sync.
+    ensureRootIsScheduled(root, eventTime);
+    schedulePendingInteractions(root, lane);
   } else {
     // Schedule a discrete update but only if it's not Sync.
     if (