make prop bindings immutable

src/runtime-with-compiler.js

@@ -23,7 +23,7 @@ Vue.prototype.$mount = function (el) {
     } else {
       template = getOuterHTML(query(el))
     }
-    options.render = new Function(compile(template, config.preserveWhiteSpace))
+    options.render = new Function(compile(template, config.preserveWhitespace))
   }
   mount.call(this, el)
 }

src/runtime/config.js

@@ -4,7 +4,7 @@ export default {
    * Preserve whitespaces between elements.
    */
 
-  preserveWhiteSpace: true,
+  preserveWhitespace: true,
 
   /**
    * Whether to suppress warnings.

src/runtime/instance/render.js

@@ -77,14 +77,16 @@ export function renderMixin (Vue) {
       this.$forceUpdate()
       return
     }
-    // set props. because props are reactive,
-    // if any of them has changed it will trigger an update.
+    // set props if they have changed.
     const attrs = data && data.attrs
     if (attrs) {
       for (let key in this.$options.props) {
-        this[key] = hasOwn(attrs, key)
+        let newVal = hasOwn(attrs, key)
           ? attrs[key]
           : attrs[hyphenate(key)]
+        if (this[key] !== newVal) {
+          this[key] = newVal
+        }
       }
     }
   }
@@ -99,7 +101,6 @@ export function renderMixin (Vue) {
       mergeParentData(this, data, parentData)
     }
     renderState.activeInstance = prev
-    console.log(vnode)
     return vnode
   }
 

src/runtime/instance/state.js

@@ -29,7 +29,7 @@ function initProps (vm) {
   if (props) {
     withoutConversion(() => {
       for (let key in props) {
-        defineReactive(vm, key, attrs[key])
+        defineReactive(vm, key, attrs[key], true /* immutable */)
       }
     })
   }

src/runtime/observer/index.js

@@ -6,7 +6,8 @@ import {
   isObject,
   isPlainObject,
   hasProto,
-  hasOwn
+  hasOwn,
+  warn
 } from '../util/index'
 
 const arrayKeys = Object.getOwnPropertyNames(arrayMethods)
@@ -192,7 +193,7 @@ export function observe (value, vm) {
  * @param {*} val
  */
 
-export function defineReactive (obj, key, val) {
+export function defineReactive (obj, key, val, immutable) {
   var dep = new Dep()
 
   var property = Object.getOwnPropertyDescriptor(obj, key)
@@ -224,18 +225,24 @@ export function defineReactive (obj, key, val) {
       }
       return value
     },
-    set: function reactiveSetter (newVal) {
-      var value = getter ? getter.call(obj) : val
-      if (newVal === value) {
-        return
+    set: immutable
+      ? function immutableSetter () {
+        if (process.env.NODE_ENV !== 'production') {
+          warn(`property "${key}" is immutable.`)
+        }
       }
-      if (setter) {
-        setter.call(obj, newVal)
-      } else {
-        val = newVal
+      : function reactiveSetter (newVal) {
+        var value = getter ? getter.call(obj) : val
+        if (newVal === value) {
+          return
+        }
+        if (setter) {
+          setter.call(obj, newVal)
+        } else {
+          val = newVal
+        }
+        childOb = observe(newVal)
+        dep.notify()
       }
-      childOb = observe(newVal)
-      dep.notify()
-    }
   })
 }