Land forked reconciler changes

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

@@ -90,8 +90,10 @@ import type {Lanes, Lane} from './ReactFiberLane.old';
 import {
   NoLane,
   NoLanes,
+  OffscreenLane,
   isSubsetOfLanes,
   mergeLanes,
+  removeLanes,
   isTransitionLane,
   intersectLanes,
   markRootEntangled,
@@ -108,6 +110,7 @@ import {StrictLegacyMode} from './ReactTypeOfMode';
 import {
   markSkippedUpdateLanes,
   isUnsafeClassRenderPhaseUpdate,
+  getWorkInProgressRootRenderLanes,
 } from './ReactFiberWorkLoop.old';
 import {
   enqueueConcurrentClassUpdate,
@@ -132,7 +135,6 @@ export type Update<State> = {|
 
 export type SharedQueue<State> = {|
   pending: Update<State> | null,
-  interleaved: Update<State> | null,
   lanes: Lanes,
 |};
 
@@ -172,7 +174,6 @@ export function initializeUpdateQueue<State>(fiber: Fiber): void {
     lastBaseUpdate: null,
     shared: {
       pending: null,
-      interleaved: null,
       lanes: NoLanes,
     },
     effects: null,
@@ -525,9 +526,23 @@ export function processUpdateQueue<State>(
 
     let update = firstBaseUpdate;
     do {
-      const updateLane = update.lane;
+      // TODO: Don't need this field anymore
       const updateEventTime = update.eventTime;
-      if (!isSubsetOfLanes(renderLanes, updateLane)) {
+
+      // An extra OffscreenLane bit is added to updates that were made to
+      // a hidden tree, so that we can distinguish them from updates that were
+      // already there when the tree was hidden.
+      const updateLane = removeLanes(update.lane, OffscreenLane);
+      const isHiddenUpdate = updateLane !== update.lane;
+
+      // Check if this update was made while the tree was hidden. If so, then
+      // it's not a "base" update and we should disregard the extra base lanes
+      // that were added to renderLanes when we entered the Offscreen tree.
+      const shouldSkipUpdate = isHiddenUpdate
+        ? !isSubsetOfLanes(getWorkInProgressRootRenderLanes(), updateLane)
+        : !isSubsetOfLanes(renderLanes, updateLane);
+
+      if (shouldSkipUpdate) {
         // Priority is insufficient. Skip this update. If this is the first
         // skipped update, the previous update/state is the new base
         // update/state.
@@ -622,17 +637,7 @@ export function processUpdateQueue<State>(
     queue.firstBaseUpdate = newFirstBaseUpdate;
     queue.lastBaseUpdate = newLastBaseUpdate;
 
-    // Interleaved updates are stored on a separate queue. We aren't going to
-    // process them during this render, but we do need to track which lanes
-    // are remaining.
-    const lastInterleaved = queue.shared.interleaved;
-    if (lastInterleaved !== null) {
-      let interleaved = lastInterleaved;
-      do {
-        newLanes = mergeLanes(newLanes, interleaved.lane);
-        interleaved = ((interleaved: any).next: Update<State>);
-      } while (interleaved !== lastInterleaved);
-    } else if (firstBaseUpdate === null) {
+    if (firstBaseUpdate === null) {
       // `queue.lanes` is used for entangling transitions. We can set it back to
       // zero once the queue is empty.
       queue.shared.lanes = NoLanes;

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

@@ -1522,17 +1522,15 @@ function completeWork(
         // at offscreen priority.
         if (includesSomeLane(subtreeRenderLanes, (OffscreenLane: Lane))) {
           bubbleProperties(workInProgress);
-          if (supportsMutation) {
-            // Check if there was an insertion or update in the hidden subtree.
-            // If so, we need to hide those nodes in the commit phase, so
-            // schedule a visibility effect.
-            if (
-              (!enableLegacyHidden ||
-                workInProgress.tag !== LegacyHiddenComponent) &&
-              workInProgress.subtreeFlags & (Placement | Update)
-            ) {
-              workInProgress.flags |= Visibility;
-            }
+          // Check if there was an insertion or update in the hidden subtree.
+          // If so, we need to hide those nodes in the commit phase, so
+          // schedule a visibility effect.
+          if (
+            (!enableLegacyHidden ||
+              workInProgress.tag !== LegacyHiddenComponent) &&
+            workInProgress.subtreeFlags & (Placement | Update)
+          ) {
+            workInProgress.flags |= Visibility;
           }
         }
       }

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

@@ -1522,17 +1522,15 @@ function completeWork(
         // at offscreen priority.
         if (includesSomeLane(subtreeRenderLanes, (OffscreenLane: Lane))) {
           bubbleProperties(workInProgress);
-          if (supportsMutation) {
-            // Check if there was an insertion or update in the hidden subtree.
-            // If so, we need to hide those nodes in the commit phase, so
-            // schedule a visibility effect.
-            if (
-              (!enableLegacyHidden ||
-                workInProgress.tag !== LegacyHiddenComponent) &&
-              workInProgress.subtreeFlags & (Placement | Update)
-            ) {
-              workInProgress.flags |= Visibility;
-            }
+          // Check if there was an insertion or update in the hidden subtree.
+          // If so, we need to hide those nodes in the commit phase, so
+          // schedule a visibility effect.
+          if (
+            (!enableLegacyHidden ||
+              workInProgress.tag !== LegacyHiddenComponent) &&
+            workInProgress.subtreeFlags & (Placement | Update)
+          ) {
+            workInProgress.flags |= Visibility;
           }
         }
       }

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

@@ -166,8 +166,14 @@ export function unsafe_markUpdateLaneFromFiberToRoot(
   sourceFiber: Fiber,
   lane: Lane,
 ): FiberRoot | null {
+  // NOTE: For Hyrum's Law reasons, if an infinite update loop is detected, it
+  // should throw before `markUpdateLaneFromFiberToRoot` is called. But this is
+  // undefined behavior and we can change it if we need to; it just so happens
+  // that, at the time of this writing, there's an internal product test that
+  // happens to rely on this.
+  const root = getRootForUpdatedFiber(sourceFiber);
   markUpdateLaneFromFiberToRoot(sourceFiber, null, lane);
-  return getRootForUpdatedFiber(sourceFiber);
+  return root;
 }
 
 function markUpdateLaneFromFiberToRoot(