fix(keep-alive): fix keep-alive with scopeId/fallthrough attrs

fix #1511

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

@@ -14,7 +14,8 @@ import {
   ComponentPublicInstance,
   Ref,
   cloneVNode,
-  provide
+  provide,
+  withScopeId
 } from '@vue/runtime-test'
 import { KeepAliveProps } from '../../src/components/KeepAlive'
 
@@ -655,4 +656,30 @@ describe('KeepAlive', () => {
     expect(spyMounted).toHaveBeenCalledTimes(3)
     expect(spyUnmounted).toHaveBeenCalledTimes(4)
   })
+
+  // #1513
+  test('should work with cloned root due to scopeId / fallthrough attrs', async () => {
+    const viewRef = ref('one')
+    const instanceRef = ref<any>(null)
+    const withId = withScopeId('foo')
+    const App = {
+      __scopeId: 'foo',
+      render: withId(() => {
+        return h(KeepAlive, null, {
+          default: () => h(views[viewRef.value], { ref: instanceRef })
+        })
+      })
+    }
+    render(h(App), root)
+    expect(serializeInner(root)).toBe(`<div foo>one</div>`)
+    instanceRef.value.msg = 'changed'
+    await nextTick()
+    expect(serializeInner(root)).toBe(`<div foo>changed</div>`)
+    viewRef.value = 'two'
+    await nextTick()
+    expect(serializeInner(root)).toBe(`<div foo>two</div>`)
+    viewRef.value = 'one'
+    await nextTick()
+    expect(serializeInner(root)).toBe(`<div foo>changed</div>`)
+  })
 })