fix(suspense): fix suspense regression for errored template component

fix #3857

packages/runtime-core/__tests__/components/Suspense.spec.ts

@@ -632,6 +632,49 @@ describe('Suspense', () => {
     expect(serializeInner(root)).toBe(`<div>oops</div>`)
   })
 
+  // #3857
+  test('error handling w/ template optimization', async () => {
+    const Async = {
+      async setup() {
+        throw new Error('oops')
+      }
+    }
+
+    const Comp = {
+      template: `
+      <div v-if="errorMessage">{{ errorMessage }}</div>
+      <Suspense v-else>
+        <div>
+          <Async />     
+        </div>
+        <template #fallback>
+          <div>fallback</div>
+        </template>
+      </Suspense>
+      `,
+      components: { Async },
+      setup() {
+        const errorMessage = ref<string | null>(null)
+        onErrorCaptured(err => {
+          errorMessage.value =
+            err instanceof Error
+              ? err.message
+              : `A non-Error value thrown: ${err}`
+          return false
+        })
+        return { errorMessage }
+      }
+    }
+
+    const root = nodeOps.createElement('div')
+    render(h(Comp), root)
+    expect(serializeInner(root)).toBe(`<div>fallback</div>`)
+
+    await Promise.all(deps)
+    await nextTick()
+    expect(serializeInner(root)).toBe(`<div>oops</div>`)
+  })
+
   it('combined usage (nested async + nested suspense + multiple deps)', async () => {
     const msg = ref('nested msg')
     const calls: number[] = []

packages/runtime-core/src/renderer.ts

@@ -1073,16 +1073,19 @@ function baseCreateRenderer(
       const newVNode = newChildren[i]
       // Determine the container (parent element) for the patch.
       const container =
+        // oldVNode may be an errored async setup() component inside Suspense
+        // which will not have a mounted element
+        oldVNode.el &&
         // - In the case of a Fragment, we need to provide the actual parent
         // of the Fragment itself so it can move its children.
-        oldVNode.type === Fragment ||
-        // - In the case of different nodes, there is going to be a replacement
-        // which also requires the correct parent container
-        !isSameVNodeType(oldVNode, newVNode) ||
-        // - In the case of a component, it could contain anything.
-        oldVNode.shapeFlag & ShapeFlags.COMPONENT ||
-        oldVNode.shapeFlag & ShapeFlags.TELEPORT
-          ? hostParentNode(oldVNode.el!)!
+        (oldVNode.type === Fragment ||
+          // - In the case of different nodes, there is going to be a replacement
+          // which also requires the correct parent container
+          !isSameVNodeType(oldVNode, newVNode) ||
+          // - In the case of a component, it could contain anything.
+          oldVNode.shapeFlag & ShapeFlags.COMPONENT ||
+          oldVNode.shapeFlag & ShapeFlags.TELEPORT)
+          ? hostParentNode(oldVNode.el)!
           : // In other cases, the parent container is not actually used so we
             // just pass the block element here to avoid a DOM parentNode call.
             fallbackContainer