packages/runtime-core/src/renderer.ts (1)

858-906: 🩺 Stability & Availability | 🔴 Critical | ⚡ Quick win

Separate non-isomorphic blocks from normal leaf nodes, and route HMR through the full-diff branch.

Line 866 can null dynamicChildren for HMR, but Line 881 still branches only on isFullDiffRequired; equal-length HMR blocks then call patchBlockChildren(..., dynamicChildren!) with null. Also, the current predicate is true when both vnodes simply have no nested dynamicChildren, forcing full children/props diffs for normal optimized dynamic leaf nodes.

Proposed fix

-    const isFullDiffRequired = !(
-      dynamicChildren &&
-      n1.dynamicChildren &&
-      n1.dynamicChildren.length === dynamicChildren.length
-    )
+    const isNonIsomorphicBlock = !!(
+      (dynamicChildren || n1.dynamicChildren) &&
+      (!dynamicChildren ||
+        !n1.dynamicChildren ||
+        n1.dynamicChildren.length !== dynamicChildren.length)
+    )
+    const forceFullDiff =
+      isNonIsomorphicBlock || (__DEV__ && isHmrUpdating)
 
     // HMR updated, force full diff
-    if (isFullDiffRequired || (__DEV__ && isHmrUpdating)) {
+    if (forceFullDiff) {
       patchFlag = 0
       optimized = false
       dynamicChildren = null
     }
@@
-    if (isFullDiffRequired) {
+    if (dynamicChildren) {
+      patchBlockChildren(
+        n1.dynamicChildren!,
+        dynamicChildren,
+        el,
+        parentComponent,
+        parentSuspense,
+        resolveChildrenNamespace(n2, namespace),
+        slotScopeIds,
+      )
+      if (__DEV__) {
+        // necessary for HMR
+        traverseStaticChildren(n1, n2)
+      }
+    } else if (!optimized) {
       patchChildren(
         n1,
         n2,
@@
         slotScopeIds,
         false,
       )
-    } else {
-      patchBlockChildren(
-        n1.dynamicChildren!,
-        dynamicChildren!,
-        el,
-        parentComponent,
-        parentSuspense,
-        resolveChildrenNamespace(n2, namespace),
-        slotScopeIds,
-      )
-      if (__DEV__) {
-        // necessary for HMR
-        traverseStaticChildren(n1, n2)
-      }
     }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/runtime-core/src/renderer.ts` around lines 858 - 906, Separate
non-isomorphic blocks from normal optimized leaf nodes, and ensure HMR always
uses the full-diff path. Update the logic around isFullDiffRequired in
renderer.ts so it only forces a full diff for user-wrapped/non-isomorphic
blocks, not for ordinary vnodes that simply lack dynamicChildren, and keep HMR
from falling through to patchBlockChildren when dynamicChildren has been nulled.
Use the existing patchChildren, patchBlockChildren, and isHmrUpdating branches
to route HMR updates through the full-diff branch and avoid calling
patchBlockChildren with null dynamicChildren.