also warn set/delete on instance root $data

src/core/instance/lifecycle.js

@@ -122,7 +122,7 @@ export function lifecycleMixin (Vue: Class<Component>) {
     }
     if (vm._watchers.length) {
       for (let i = 0; i < vm._watchers.length; i++) {
-        vm._watchers[i].update()
+        vm._watchers[i].update(true /* shallow */)
       }
     }
   }
@@ -150,7 +150,7 @@ export function lifecycleMixin (Vue: Class<Component>) {
     // remove reference from data ob
     // frozen object may not have observer.
     if (vm._data.__ob__) {
-      vm._data.__ob__.removeVm(vm)
+      vm._data.__ob__.vmCount--
     }
     // call the last hook...
     vm._isDestroyed = true

src/core/instance/state.js

@@ -62,7 +62,8 @@ function initData (vm: Component) {
     proxy(vm, keys[i])
   }
   // observe data
-  observe(data, vm)
+  observe(data)
+  data.__ob__.vmCount++
 }
 
 const computedSharedDefinition = {
@@ -205,7 +206,8 @@ function setData (vm: Component, newData: Object) {
       proxy(vm, key)
     }
   }
-  oldData.__ob__.removeVm(vm)
-  observe(newData, vm)
+  oldData.__ob__.vmCount--
+  observe(newData)
+  newData.__ob__.vmCount++
   vm.$forceUpdate()
 }

src/core/observer/index.js

@@ -5,7 +5,6 @@ import Dep from './dep'
 import { arrayMethods } from './array'
 import {
   def,
-  remove,
   isObject,
   isPlainObject,
   hasProto,
@@ -35,12 +34,12 @@ export const observerState = {
 export class Observer {
   value: any;
   dep: Dep;
-  vms: ?Array<Component>;
+  vmCount: number; // number of vms that has this object as root $data
 
   constructor (value: any) {
     this.value = value
     this.dep = new Dep()
-    this.vms = null
+    this.vmCount = 0
     def(value, '__ob__', this)
     if (Array.isArray(value)) {
       const augment = hasProto
@@ -73,24 +72,6 @@ export class Observer {
       observe(items[i])
     }
   }
-
-  /**
-   * Add an owner vm, so that when $set/$delete mutations
-   * happen we can notify owner vms to proxy the keys and
-   * digest the watchers. This is only called when the object
-   * is observed as an instance's root $data.
-   */
-  addVm (vm: Component) {
-    (this.vms || (this.vms = [])).push(vm)
-  }
-
-  /**
-   * Remove an owner vm. This is called when the object is
-   * swapped out as an instance's $data object.
-   */
-  removeVm (vm: Component) {
-    remove(this.vms, vm)
-  }
 }
 
 // helpers
@@ -123,7 +104,7 @@ function copyAugment (target: Object, src: Object, keys: Array<string>) {
  * returns the new observer if successfully observed,
  * or the existing observer if the value already has one.
  */
-export function observe (value: any, vm?: Component): Observer | void {
+export function observe (value: any): Observer | void {
   if (!isObject(value)) {
     return
   }
@@ -139,9 +120,6 @@ export function observe (value: any, vm?: Component): Observer | void {
   ) {
     ob = new Observer(value)
   }
-  if (ob && vm) {
-    ob.addVm(vm)
-  }
   return ob
 }
 
@@ -210,28 +188,20 @@ export function set (obj: Array<any> | Object, key: any, val: any) {
     obj[key] = val
     return
   }
-  if (obj._isVue) {
+  const ob = obj.__ob__
+  if (obj._isVue || (ob && ob.vmCount)) {
     process.env.NODE_ENV !== 'production' && warn(
-      'Do not add reactive properties to a Vue instance at runtime - ' +
-      'delcare it upfront in the data option.'
+      'Avoid adding reactive properties to a Vue instance or its root $data ' +
+      'at runtime - delcare it upfront in the data option.'
     )
     return
   }
-  const ob = obj.__ob__
   if (!ob) {
     obj[key] = val
     return
   }
   defineReactive(ob.value, key, val)
   ob.dep.notify()
-  if (ob.vms) {
-    let i = ob.vms.length
-    while (i--) {
-      const vm = ob.vms[i]
-      proxy(vm, key)
-      vm.$forceUpdate()
-    }
-  }
   return val
 }
 
@@ -239,9 +209,11 @@ export function set (obj: Array<any> | Object, key: any, val: any) {
  * Delete a property and trigger change if necessary.
  */
 export function del (obj: Object, key: string) {
-  if (obj._isVue) {
+  const ob = obj.__ob__
+  if (obj._isVue || (ob && ob.vmCount)) {
     process.env.NODE_ENV !== 'production' && warn(
-      'Do not delete properties on a Vue instance - just set it to null.'
+      'Avoid deleting properties on a Vue instance or its root $data ' +
+      '- just set it to null.'
     )
     return
   }
@@ -249,19 +221,10 @@ export function del (obj: Object, key: string) {
     return
   }
   delete obj[key]
-  const ob = obj.__ob__
   if (!ob) {
     return
   }
   ob.dep.notify()
-  if (ob.vms) {
-    let i = ob.vms.length
-    while (i--) {
-      const vm = ob.vms[i]
-      unproxy(vm, key)
-      vm.$forceUpdate()
-    }
-  }
 }
 
 export function proxy (vm: Component, key: string) {

test/unit/features/instance/methods-lifecycle.spec.js

@@ -60,7 +60,7 @@ describe('Instance methods lifecycle', () => {
     it('remove self from data observer', () => {
       const vm = new Vue({ data: { a: 1 }})
       vm.$destroy()
-      expect(vm.$data.__ob__.vms.length).toBe(0)
+      expect(vm.$data.__ob__.vmCount).toBe(0)
     })
 
     it('avoid duplicate calls', () => {

test/unit/modules/observer/observer.spec.js

@@ -290,13 +290,33 @@ describe('Observer', () => {
     Vue.set(vm, 'a', 2)
     waitForUpdate(() => {
       expect(vm.$el.outerHTML).toBe('<div>2</div>')
-      expect('Do not add reactive properties to a Vue instance').not.toHaveBeenWarned()
+      expect('Avoid adding reactive properties to a Vue instance').not.toHaveBeenWarned()
       Vue.delete(vm, 'a')
     }).then(() => {
-      expect('Do not delete properties on a Vue instance').toHaveBeenWarned()
+      expect('Avoid deleting properties on a Vue instance').toHaveBeenWarned()
       expect(vm.$el.outerHTML).toBe('<div>2</div>')
       Vue.set(vm, 'b', 123)
-      expect('Do not add reactive properties to a Vue instance').toHaveBeenWarned()
+      expect('Avoid adding reactive properties to a Vue instance').toHaveBeenWarned()
+    }).then(done)
+  })
+
+  it('warning set/delete on Vue instance root $data', done => {
+    const data = { a: 1 }
+    const vm = new Vue({
+      template: '<div>{{a}}</div>',
+      data
+    }).$mount()
+    expect(vm.$el.outerHTML).toBe('<div>1</div>')
+    Vue.set(data, 'a', 2)
+    waitForUpdate(() => {
+      expect(vm.$el.outerHTML).toBe('<div>2</div>')
+      expect('Avoid adding reactive properties to a Vue instance').not.toHaveBeenWarned()
+      Vue.delete(data, 'a')
+    }).then(() => {
+      expect('Avoid deleting properties on a Vue instance').toHaveBeenWarned()
+      expect(vm.$el.outerHTML).toBe('<div>2</div>')
+      Vue.set(data, 'b', 123)
+      expect('Avoid adding reactive properties to a Vue instance').toHaveBeenWarned()
     }).then(done)
   })