fix(hmr): avoid hydration for hmr updating (vuejs#12262)

close vuejs#7706
close vuejs#8170

Author: edison1105

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

@@ -32,10 +32,13 @@ import {
   withCtx,
   withDirectives,
 } from '@vue/runtime-dom'
+import type { HMRRuntime } from '../src/hmr'
 import { type SSRContext, renderToString } from '@vue/server-renderer'
 import { PatchFlags, normalizeStyle } from '@vue/shared'
 import { vShowOriginalDisplay } from '../../runtime-dom/src/directives/vShow'
-import { expect } from 'vitest'
+
+declare var __VUE_HMR_RUNTIME__: HMRRuntime
+const { createRecord, reload } = __VUE_HMR_RUNTIME__
 
 function mountWithHydration(html: string, render: () => any) {
   const container = document.createElement('div')
@@ -1843,6 +1846,40 @@ describe('SSR hydration', () => {
     }
   })
 
+  test('hmr reload child wrapped in KeepAlive', async () => {
+    const id = 'child-reload'
+    const Child = {
+      __hmrId: id,
+      template: `<div>foo</div>`,
+    }
+    createRecord(id, Child)
+
+    const appId = 'test-app-id'
+    const App = {
+      __hmrId: appId,
+      components: { Child },
+      template: `
+      <div>
+        <KeepAlive>
+          <Child />
+        </KeepAlive>
+      </div>
+      `,
+    }
+
+    const root = document.createElement('div')
+    root.innerHTML = await renderToString(h(App))
+    createSSRApp(App).mount(root)
+    expect(root.innerHTML).toBe('<div><div>foo</div></div>')
+
+    reload(id, {
+      __hmrId: id,
+      template: `<div>bar</div>`,
+    })
+    await nextTick()
+    expect(root.innerHTML).toBe('<div><div>bar</div></div>')
+  })
+
   describe('mismatch handling', () => {
     test('text node', () => {
       const { container } = mountWithHydration(`foo`, () => 'bar')

packages/runtime-core/src/renderer.ts

@@ -1208,12 +1208,12 @@ function baseCreateRenderer(
       }
     }
 
+    // avoid hydration for hmr updating
+    if (__DEV__ && isHmrUpdating) initialVNode.el = null
+
     // setup() is async. This component relies on async logic to be resolved
     // before proceeding
     if (__FEATURE_SUSPENSE__ && instance.asyncDep) {
-      // avoid hydration for hmr updating
-      if (__DEV__ && isHmrUpdating) initialVNode.el = null
-
       parentSuspense &&
         parentSuspense.registerDep(instance, setupRenderEffect, optimized)