fix(runtime-core/refs): handle multiple merged refs for dynamic component with vnode

fix #2078

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

@@ -6,7 +6,8 @@ import {
   nextTick,
   defineComponent,
   reactive,
-  serializeInner
+  serializeInner,
+  shallowRef
 } from '@vue/runtime-test'
 
 // reference: https://vue-composition-api-rfc.netlify.com/api.html#template-refs
@@ -325,4 +326,43 @@ describe('api: template refs', () => {
     await nextTick()
     expect(spy.mock.calls[1][0]).toBe('p')
   })
+
+  // #2078
+  test('handling multiple merged refs', async () => {
+    const Foo = {
+      render: () => h('div', 'foo')
+    }
+    const Bar = {
+      render: () => h('div', 'bar')
+    }
+
+    const viewRef = shallowRef<any>(Foo)
+    const elRef1 = ref()
+    const elRef2 = ref()
+
+    const App = {
+      render() {
+        if (!viewRef.value) {
+          return null
+        }
+        const view = h(viewRef.value, { ref: elRef1 })
+        return h(view, { ref: elRef2 })
+      }
+    }
+    const root = nodeOps.createElement('div')
+    render(h(App), root)
+
+    expect(serializeInner(elRef1.value.$el)).toBe('foo')
+    expect(elRef1.value).toBe(elRef2.value)
+
+    viewRef.value = Bar
+    await nextTick()
+    expect(serializeInner(elRef1.value.$el)).toBe('bar')
+    expect(elRef1.value).toBe(elRef2.value)
+
+    viewRef.value = null
+    await nextTick()
+    expect(elRef1.value).toBeNull()
+    expect(elRef1.value).toBe(elRef2.value)
+  })
 })