fix(runtime-core): v-model listeners that already exists on the component should not be merged (#2011)

fix #1989

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

@@ -594,4 +594,61 @@ describe('attribute fallthrough', () => {
     button.dispatchEvent(new CustomEvent('click'))
     expect(click).toHaveBeenCalled()
   })
+
+  // #1989
+  it('should not fallthrough v-model listeners with corresponding declared prop', () => {
+    let textFoo = ''
+    let textBar = ''
+    const click = jest.fn()
+
+    const App = defineComponent({
+      setup() {
+        return () =>
+          h(Child, {
+            modelValue: textFoo,
+            'onUpdate:modelValue': (val: string) => {
+              textFoo = val
+            }
+          })
+      }
+    })
+
+    const Child = defineComponent({
+      props: ['modelValue'],
+      setup(_props, { emit }) {
+        return () =>
+          h(GrandChild, {
+            modelValue: textBar,
+            'onUpdate:modelValue': (val: string) => {
+              textBar = val
+              emit('update:modelValue', 'from Child')
+            }
+          })
+      }
+    })
+
+    const GrandChild = defineComponent({
+      props: ['modelValue'],
+      setup(_props, { emit }) {
+        return () =>
+          h('button', {
+            onClick() {
+              click()
+              emit('update:modelValue', 'from GrandChild')
+            }
+          })
+      }
+    })
+
+    const root = document.createElement('div')
+    document.body.appendChild(root)
+    render(h(App), root)
+
+    const node = root.children[0] as HTMLElement
+
+    node.dispatchEvent(new CustomEvent('click'))
+    expect(click).toHaveBeenCalled()
+    expect(textBar).toBe('from GrandChild')
+    expect(textFoo).toBe('from Child')
+  })
 })