fix vuejs#539 v-if duplicate compile when a different truthy value is set

Author: yyx990803

src/directives/if.js

@@ -43,6 +43,11 @@ module.exports = {
   },
 
   insert: function () {
+    // avoid duplicate inserts, since update() can be
+    // called with different truthy values
+    if (this.decompile) {
+      return
+    }
     var vm = this.vm
     var frag = templateParser.clone(this.template)
     var decompile = this.linker(vm, frag)

test/unit/specs/directives/if_spec.js

@@ -145,6 +145,22 @@ if (_.inBrowser) {
       })
     })
 
+    it('v-if with different truthy values', function (done) {
+      var vm = new Vue({
+        el: el,
+        data: {
+          a: 1
+        },
+        template: '<div v-if="a">{{a}}</div>'
+      })
+      expect(el.innerHTML).toBe(wrap('<div>1</div>'))
+      vm.a = 2
+      _.nextTick(function () {
+        expect(el.innerHTML).toBe(wrap('<div>2</div>'))
+        done()
+      })
+    })
+
     it('invalid warn', function () {
       el.setAttribute('v-if', 'test')
       var vm = new Vue({