fix(hmr): prevent update unmounting component during HMR reload (#13815)

close vitejs/vite-plugin-vue#599

Author: edison1105

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

@@ -937,4 +937,55 @@ describe('hot module replacement', () => {
     rerender(id, () => 'bar')
     expect(serializeInner(root)).toBe('bar')
   })
+
+  // https://github.com/vitejs/vite-plugin-vue/issues/599
+  // Both Outer and Inner are reloaded when './server.js' changes
+  test('reload nested components from single update', async () => {
+    const innerId = 'nested-reload-inner'
+    const outerId = 'nested-reload-outer'
+
+    let Inner = {
+      __hmrId: innerId,
+      render() {
+        return h('div', 'foo')
+      },
+    }
+    let Outer = {
+      __hmrId: outerId,
+      render() {
+        return h(Inner)
+      },
+    }
+
+    createRecord(innerId, Inner)
+    createRecord(outerId, Outer)
+
+    const App = {
+      render: () => h(Outer),
+    }
+
+    const root = nodeOps.createElement('div')
+    render(h(App), root)
+    expect(serializeInner(root)).toBe('<div>foo</div>')
+
+    Inner = {
+      __hmrId: innerId,
+      render() {
+        return h('div', 'bar')
+      },
+    }
+    Outer = {
+      __hmrId: outerId,
+      render() {
+        return h(Inner)
+      },
+    }
+
+    // trigger reload for both Outer and Inner
+    reload(outerId, Outer)
+    reload(innerId, Inner)
+    await nextTick()
+
+    expect(serializeInner(root)).toBe('<div>bar</div>')
+  })
 })