fix(ssr): hydrate strings in fragments

packages/runtime-core/__tests__/hydration.spec.ts

@@ -17,6 +17,7 @@ import {
 } from '@vue/runtime-dom'
 import { renderToString, SSRContext } from '@vue/server-renderer'
 import { PatchFlags } from '../../shared/src'
+import { renderSlot } from '../src/helpers/renderSlot'
 
 function mountWithHydration(html: string, render: () => any) {
   const container = document.createElement('div')
@@ -851,6 +852,26 @@ describe('SSR hydration', () => {
     expect((container.firstChild!.firstChild as any)._value).toBe(true)
   })
 
+  test('components with fragments', () => {
+    const { container } = mountWithHydration(
+      '<!--[-->foo<!--]-->',
+      () =>
+        h(defineComponent({
+          props: {
+            title: {
+              type: String,
+              required: true,
+            },
+          },
+
+          render() {
+            return renderSlot(this.$slots, 'title', undefined, () => [this.title])
+          }
+        }), { title: 'foo' })
+    )
+    expect(container.textContent).toBe('foo')
+  })
+
   describe('mismatch handling', () => {
     test('text node', () => {
       const { container } = mountWithHydration(`foo`, () => 'bar')

packages/runtime-core/src/hydration.ts

@@ -385,7 +385,6 @@ export function createHydrationFunctions(
     slotScopeIds: string[] | null,
     optimized: boolean
   ): Node | null => {
-    optimized = optimized || !!parentVNode.dynamicChildren
     const children = parentVNode.children as VNode[]
     const l = children.length
     let hasWarned = false