From ba4bdb2ab5e15398fb2ffaafe944a1de56851734 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Markb=C3=A5ge?= <sebastian@calyptus.eu>
Date: Mon, 4 Aug 2025 13:04:47 -0400
Subject: [PATCH] [DevTools] Consume SuspenseNodes that were skipped when we're
 bailing out of a subtree (#34082)

This searches through the remaining children to see if any of them were
children of the bailed out FiberInstance and if so we should reuse them
in the new set. It's faster to do this than search through children of
the FiberInstance for Suspense boundaries.
---
 .../src/backend/fiber/renderer.js             | 96 +++++++++++++++++--
 1 file changed, 87 insertions(+), 9 deletions(-)

diff --git a/packages/react-devtools-shared/src/backend/fiber/renderer.js b/packages/react-devtools-shared/src/backend/fiber/renderer.js
index 5ffa5251dc..b6bc24dd01 100644
--- a/packages/react-devtools-shared/src/backend/fiber/renderer.js
+++ b/packages/react-devtools-shared/src/backend/fiber/renderer.js
@@ -2701,6 +2701,76 @@ export function attach(
     }
   }
 
+  function isChildOf(
+    parentInstance: DevToolsInstance,
+    childInstance: DevToolsInstance,
+    grandParent: DevToolsInstance,
+  ): boolean {
+    let instance = childInstance.parent;
+    while (instance !== null) {
+      if (parentInstance === instance) {
+        return true;
+      }
+      if (instance === parentInstance.parent || instance === grandParent) {
+        // This was a sibling but not inside the FiberInstance. We can bail out.
+        break;
+      }
+      instance = instance.parent;
+    }
+    return false;
+  }
+
+  function consumeSuspenseNodesOfExistingInstance(
+    instance: DevToolsInstance,
+  ): void {
+    // We need to also consume any unchanged Suspense boundaries.
+    let suspenseNode = remainingReconcilingChildrenSuspenseNodes;
+    if (suspenseNode === null) {
+      return;
+    }
+    const parentSuspenseNode = reconcilingParentSuspenseNode;
+    if (parentSuspenseNode === null) {
+      throw new Error(
+        'The should not be any remaining suspense node children if there is no parent.',
+      );
+    }
+    let foundOne = false;
+    let previousSkippedSibling = null;
+    while (suspenseNode !== null) {
+      // Check if this SuspenseNode was a child of the bailed out FiberInstance.
+      if (
+        isChildOf(instance, suspenseNode.instance, parentSuspenseNode.instance)
+      ) {
+        foundOne = true;
+        // The suspenseNode was child of the bailed out Fiber.
+        // First, remove it from the remaining children set.
+        const nextRemainingSibling = suspenseNode.nextSibling;
+        if (previousSkippedSibling === null) {
+          remainingReconcilingChildrenSuspenseNodes = nextRemainingSibling;
+        } else {
+          previousSkippedSibling.nextSibling = nextRemainingSibling;
+        }
+        suspenseNode.nextSibling = null;
+        // Then, re-insert it into the newly reconciled set.
+        if (previouslyReconciledSiblingSuspenseNode === null) {
+          parentSuspenseNode.firstChild = suspenseNode;
+        } else {
+          previouslyReconciledSiblingSuspenseNode.nextSibling = suspenseNode;
+        }
+        previouslyReconciledSiblingSuspenseNode = suspenseNode;
+        // Continue
+        suspenseNode = nextRemainingSibling;
+      } else if (foundOne) {
+        // If we found one and then hit a miss, we assume that we're passed the sequence because
+        // they should've all been consecutive.
+        break;
+      } else {
+        previousSkippedSibling = suspenseNode;
+        suspenseNode = suspenseNode.nextSibling;
+      }
+    }
+  }
+
   function mountVirtualInstanceRecursively(
     virtualInstance: VirtualInstance,
     firstChild: Fiber,
@@ -3094,9 +3164,11 @@ export function attach(
       reconcilingParent = stashedParent;
       previouslyReconciledSibling = stashedPrevious;
       remainingReconcilingChildren = stashedRemaining;
-      reconcilingParentSuspenseNode = stashedSuspenseParent;
-      previouslyReconciledSiblingSuspenseNode = stashedSuspensePrevious;
-      remainingReconcilingChildrenSuspenseNodes = stashedSuspenseRemaining;
+      if (instance.suspenseNode !== null) {
+        reconcilingParentSuspenseNode = stashedSuspenseParent;
+        previouslyReconciledSiblingSuspenseNode = stashedSuspensePrevious;
+        remainingReconcilingChildrenSuspenseNodes = stashedSuspenseRemaining;
+      }
     }
     if (instance.kind === FIBER_INSTANCE) {
       recordUnmount(instance);
@@ -3688,10 +3760,12 @@ export function attach(
       fiberInstance.firstChild = null;
       fiberInstance.suspendedBy = null;
 
-      if (fiberInstance.suspenseNode !== null) {
-        reconcilingParentSuspenseNode = fiberInstance.suspenseNode;
+      const suspenseNode = fiberInstance.suspenseNode;
+      if (suspenseNode !== null) {
+        reconcilingParentSuspenseNode = suspenseNode;
         previouslyReconciledSiblingSuspenseNode = null;
-        remainingReconcilingChildrenSuspenseNodes = null;
+        remainingReconcilingChildrenSuspenseNodes = suspenseNode.firstChild;
+        suspenseNode.firstChild = null;
       }
     }
     try {
@@ -3849,6 +3923,8 @@ export function attach(
             fiberInstance.firstChild = remainingReconcilingChildren;
             remainingReconcilingChildren = null;
 
+            consumeSuspenseNodesOfExistingInstance(fiberInstance);
+
             if (traceUpdatesEnabled) {
               // If we're tracing updates and we've bailed out before reaching a host node,
               // we should fall back to recursively marking the nearest host descendants for highlight.
@@ -3919,9 +3995,11 @@ export function attach(
         reconcilingParent = stashedParent;
         previouslyReconciledSibling = stashedPrevious;
         remainingReconcilingChildren = stashedRemaining;
-        reconcilingParentSuspenseNode = stashedSuspenseParent;
-        previouslyReconciledSiblingSuspenseNode = stashedSuspensePrevious;
-        remainingReconcilingChildrenSuspenseNodes = stashedSuspenseRemaining;
+        if (fiberInstance.suspenseNode !== null) {
+          reconcilingParentSuspenseNode = stashedSuspenseParent;
+          previouslyReconciledSiblingSuspenseNode = stashedSuspensePrevious;
+          remainingReconcilingChildrenSuspenseNodes = stashedSuspenseRemaining;
+        }
       }
     }
   }