fix(runtime-core/template-ref): template ref used in the same template should trigger update

fix #1505

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

@@ -5,7 +5,8 @@ import {
   render,
   nextTick,
   defineComponent,
-  reactive
+  reactive,
+  serializeInner
 } from '@vue/runtime-test'
 
 // reference: https://vue-composition-api-rfc.netlify.com/api.html#template-refs
@@ -246,4 +247,25 @@ describe('api: template refs', () => {
     expect(refKey2.value).toBe(root.children[2])
     expect(refKey3.value).toBe(root.children[3])
   })
+
+  // #1505
+  test('reactive template ref in the same template', async () => {
+    const Comp = {
+      setup() {
+        const el = ref()
+        return { el }
+      },
+      render(this: any) {
+        return h('div', { id: 'foo', ref: 'el' }, this.el && this.el.props.id)
+      }
+    }
+
+    const root = nodeOps.createElement('div')
+    render(h(Comp), root)
+    // ref not ready on first render, but should queue an update immediately
+    expect(serializeInner(root)).toBe(`<div id="foo"></div>`)
+    await nextTick()
+    // ref should be updated
+    expect(serializeInner(root)).toBe(`<div id="foo">foo</div>`)
+  })
 })