Suspense fuzz tester

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -1178,7 +1178,6 @@ function updateSuspenseComponent(
           currentPrimaryChildFragment.pendingProps,
           NoWork,
         );
-        primaryChildFragment.effectTag |= Placement;
 
         if ((workInProgress.mode & ConcurrentMode) === NoContext) {
           // Outside of concurrent mode, we commit the effects from the
@@ -1213,7 +1212,6 @@ function updateSuspenseComponent(
           nextFallbackChildren,
           currentFallbackChildFragment.expirationTime,
         ));
-        fallbackChildFragment.effectTag |= Placement;
         child = primaryChildFragment;
         primaryChildFragment.childExpirationTime = NoWork;
         // Skip the primary children, and continue working on the
@@ -1257,11 +1255,14 @@ function updateSuspenseComponent(
           NoWork,
           null,
         );
-
-        primaryChildFragment.effectTag |= Placement;
         primaryChildFragment.child = currentPrimaryChild;
         currentPrimaryChild.return = primaryChildFragment;
 
+        // Even though we're creating a new fiber, there are no new children,
+        // because we're reusing an already mounted tree. So we don't need to
+        // schedule a placement.
+        // primaryChildFragment.effectTag |= Placement;
+
         if ((workInProgress.mode & ConcurrentMode) === NoContext) {
           // Outside of concurrent mode, we commit the effects from the
           // partially completed, timed-out tree, too.

packages/react-reconciler/src/ReactFiberCommitWork.js

@@ -558,6 +558,16 @@ function hideOrUnhideAllChildren(finishedWork, isHidden) {
         } else {
           unhideTextInstance(instance, node.memoizedProps);
         }
+      } else if (
+        node.tag === SuspenseComponent &&
+        node.memoizedState !== null
+      ) {
+        // Found a nested Suspense component that timed out. Skip over the
+        // primary child fragment, which should remain hidden.
+        const fallbackChildFragment: Fiber = (node.child: any).sibling;
+        fallbackChildFragment.return = node;
+        node = fallbackChildFragment;
+        continue;
       } else if (node.child !== null) {
         node.child.return = node;
         node = node.child;

packages/react-reconciler/src/ReactFiberCompleteWork.js

@@ -45,6 +45,7 @@ import {
   Update,
   NoEffect,
   DidCapture,
+  Deletion,
 } from 'shared/ReactSideEffectTags';
 import invariant from 'shared/invariant';
 
@@ -82,7 +83,6 @@ import {
   popHydrationState,
 } from './ReactFiberHydrationContext';
 import {ConcurrentMode, NoContext} from './ReactTypeOfMode';
-import {reconcileChildFibers} from './ReactChildFiber';
 
 function markUpdate(workInProgress: Fiber) {
   // Tag the fiber with an update effect. This turns a Placement into
@@ -715,12 +715,16 @@ function completeWork(
         // the stateNode during the begin phase?
         const currentFallbackChild: Fiber | null = (current.child: any).sibling;
         if (currentFallbackChild !== null) {
-          reconcileChildFibers(
-            workInProgress,
-            currentFallbackChild,
-            null,
-            renderExpirationTime,
-          );
+          // Deletions go at the beginning of the return fiber's effect list
+          const first = workInProgress.firstEffect;
+          if (first !== null) {
+            workInProgress.firstEffect = currentFallbackChild;
+            currentFallbackChild.nextEffect = first;
+          } else {
+            workInProgress.firstEffect = workInProgress.lastEffect = currentFallbackChild;
+            currentFallbackChild.nextEffect = null;
+          }
+          currentFallbackChild.effectTag = Deletion;
         }
       }
 

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -1747,6 +1747,46 @@ function scheduleWorkToRoot(fiber: Fiber, expirationTime): FiberRoot | null {
     }
   }
 
+  if (enableSchedulerTracing) {
+    if (root !== null) {
+      const interactions = __interactionsRef.current;
+      if (interactions.size > 0) {
+        const pendingInteractionMap = root.pendingInteractionMap;
+        const pendingInteractions = pendingInteractionMap.get(expirationTime);
+        if (pendingInteractions != null) {
+          interactions.forEach(interaction => {
+            if (!pendingInteractions.has(interaction)) {
+              // Update the pending async work count for previously unscheduled interaction.
+              interaction.__count++;
+            }
+
+            pendingInteractions.add(interaction);
+          });
+        } else {
+          pendingInteractionMap.set(expirationTime, new Set(interactions));
+
+          // Update the pending async work count for the current interactions.
+          interactions.forEach(interaction => {
+            interaction.__count++;
+          });
+        }
+
+        const subscriber = __subscriberRef.current;
+        if (subscriber !== null) {
+          const threadID = computeThreadID(
+            expirationTime,
+            root.interactionThreadID,
+          );
+          subscriber.onWorkScheduled(interactions, threadID);
+        }
+      }
+    }
+  }
+  return root;
+}
+
+function scheduleWork(fiber: Fiber, expirationTime: ExpirationTime) {
+  const root = scheduleWorkToRoot(fiber, expirationTime);
   if (root === null) {
     if (__DEV__) {
       switch (fiber.tag) {
@@ -1761,49 +1801,6 @@ function scheduleWorkToRoot(fiber: Fiber, expirationTime): FiberRoot | null {
           break;
       }
     }
-    return null;
-  }
-
-  if (enableSchedulerTracing) {
-    const interactions = __interactionsRef.current;
-    if (interactions.size > 0) {
-      const pendingInteractionMap = root.pendingInteractionMap;
-      const pendingInteractions = pendingInteractionMap.get(expirationTime);
-      if (pendingInteractions != null) {
-        interactions.forEach(interaction => {
-          if (!pendingInteractions.has(interaction)) {
-            // Update the pending async work count for previously unscheduled interaction.
-            interaction.__count++;
-          }
-
-          pendingInteractions.add(interaction);
-        });
-      } else {
-        pendingInteractionMap.set(expirationTime, new Set(interactions));
-
-        // Update the pending async work count for the current interactions.
-        interactions.forEach(interaction => {
-          interaction.__count++;
-        });
-      }
-
-      const subscriber = __subscriberRef.current;
-      if (subscriber !== null) {
-        const threadID = computeThreadID(
-          expirationTime,
-          root.interactionThreadID,
-        );
-        subscriber.onWorkScheduled(interactions, threadID);
-      }
-    }
-  }
-
-  return root;
-}
-
-function scheduleWork(fiber: Fiber, expirationTime: ExpirationTime) {
-  const root = scheduleWorkToRoot(fiber, expirationTime);
-  if (root === null) {
     return;
   }