do not warn for absent non-required prop (close #1070)

Author: yyx990803

src/util/component.js

@@ -59,6 +59,11 @@ exports.initProp = function (vm, prop, value) {
  */
 
 exports.assertProp = function (prop, value) {
+  // if a prop is not provided and is not required,
+  // skip the check.
+  if (prop.raw === null && !prop.required) {
+    return true
+  }
   var options = prop.options
   var type = options.type
   var valid = true

test/unit/specs/directives/prop_spec.js

@@ -447,7 +447,7 @@ if (_.inBrowser) {
       }))
     })
 
-    it('should initialize with default value when not provided & has default data', function () {
+    it('should initialize with default value when not provided & has default data', function (done) {
       var vm = new Vue({
         el: el,
         template: '<test></test>',
@@ -469,10 +469,28 @@ if (_.inBrowser) {
         }
       })
       expect(vm.$el.textContent).toBe('hello world')
-      expect(JSON.stringify(vm.$children[0].$data)).toBe(JSON.stringify({
-        other: 'world',
-        prop: 'hello'
-      }))
+      vm.$children[0].prop = 'bye'
+      _.nextTick(function () {
+        expect(vm.$el.textContent).toBe('bye world')
+        done()
+      })
+    })
+
+    it('should not warn for non-required, absent prop', function () {
+      new Vue({
+        el: el,
+        template: '<test></test>',
+        components: {
+          test: {
+            props: {
+              prop: {
+                type: String
+              }
+            }
+          }
+        }
+      })
+      expect(_.warn).not.toHaveBeenCalled()
     })
   })
 }