remove codegen v-for truthiness check (fix #3817)

Author: yyx990803

src/compiler/codegen/index.js

@@ -89,7 +89,7 @@ function genFor (el: any): string {
   const iterator1 = el.iterator1 ? `,${el.iterator1}` : ''
   const iterator2 = el.iterator2 ? `,${el.iterator2}` : ''
   el.forProcessed = true // avoid recursion
-  return `(${exp})&&_l((${exp}),` +
+  return `_l((${exp}),` +
     `function(${alias}${iterator1}${iterator2}){` +
       `return ${genElement(el)}` +
     '})'

test/unit/modules/compiler/codegen.spec.js

@@ -40,16 +40,16 @@ describe('codegen', () => {
   it('generate v-for directive', () => {
     assertCodegen(
       '<li v-for="item in items" :key="item.uid"></li>',
-      `with(this){return (items)&&_l((items),function(item){return _h('li',{key:item.uid})})}`
+      `with(this){return _l((items),function(item){return _h('li',{key:item.uid})})}`
     )
     // iterator syntax
     assertCodegen(
       '<li v-for="(item, i) in items"></li>',
-      `with(this){return (items)&&_l((items),function(item,i){return _h('li')})}`
+      `with(this){return _l((items),function(item,i){return _h('li')})}`
     )
     assertCodegen(
       '<li v-for="(item, key, index) in items"></li>',
-      `with(this){return (items)&&_l((items),function(item,key,index){return _h('li')})}`
+      `with(this){return _l((items),function(item,key,index){return _h('li')})}`
     )
   })
 
@@ -77,7 +77,7 @@ describe('codegen', () => {
   it('generate ref on v-for', () => {
     assertCodegen(
       '<ul><li v-for="item in items" ref="component1"></li></ul>',
-      `with(this){return _h('ul',[(items)&&_l((items),function(item){return _h('li',{ref:"component1",refInFor:true})})])}`
+      `with(this){return _h('ul',[_l((items),function(item){return _h('li',{ref:"component1",refInFor:true})})])}`
     )
   })
 
@@ -304,7 +304,7 @@ describe('codegen', () => {
   it('generate static trees inside v-for', () => {
     assertCodegen(
       `<div><div v-for="i in 10"><span></span></div></div>`,
-      `with(this){return _h('div',[(10)&&_l((10),function(i){return _h('div',[_m(0,true)])})])}`,
+      `with(this){return _h('div',[_l((10),function(i){return _h('div',[_m(0,true)])})])}`,
       [`with(this){return _h('span')}`]
     )
   })