fix(vue): properly cache runtime compilation

packages/vue/__tests__/index.spec.ts

@@ -4,7 +4,7 @@ import { mockWarn } from '@vue/runtime-test'
 describe('compiler + runtime integration', () => {
   mockWarn()
 
-  it('should support on-the-fly template compilation', () => {
+  it('should support runtime template compilation', () => {
     const container = document.createElement('div')
     const App = {
       template: `{{ count }}`,
@@ -18,6 +18,43 @@ describe('compiler + runtime integration', () => {
     expect(container.innerHTML).toBe(`0`)
   })
 
+  it('should support runtime template via CSS ID selector', () => {
+    const container = document.createElement('div')
+    const template = document.createElement('div')
+    template.id = 'template'
+    template.innerHTML = '{{ count }}'
+    document.body.appendChild(template)
+
+    const App = {
+      template: `#template`,
+      data() {
+        return {
+          count: 0
+        }
+      }
+    }
+    createApp().mount(App, container)
+    expect(container.innerHTML).toBe(`0`)
+  })
+
+  it('should support runtime template via direct DOM node', () => {
+    const container = document.createElement('div')
+    const template = document.createElement('div')
+    template.id = 'template'
+    template.innerHTML = '{{ count }}'
+
+    const App = {
+      template,
+      data() {
+        return {
+          count: 0
+        }
+      }
+    }
+    createApp().mount(App, container)
+    expect(container.innerHTML).toBe(`0`)
+  })
+
   it('should warn template compilation errors with codeframe', () => {
     const container = document.createElement('div')
     const App = {