fix(vue/valid-v-for): allow using an empty alias in value

Author: rzzf

lib/rules/valid-v-for.js

@@ -163,7 +163,7 @@ module.exports = {
         const key = lhs[1]
         const index = lhs[2]
 
-        if (value === null) {
+        if (value === null && !key) {
           context.report({
             node: expr,
             messageId: 'invalidEmptyAlias'

tests/lib/rules/valid-v-for.js

@@ -46,6 +46,14 @@ tester.run('valid-v-for', rule, {
       filename: 'test.vue',
       code: '<template><div><your-component v-for="x in list" :key="x.id"></your-component></div></template>'
     },
+    {
+      filename: 'test.vue',
+      code: '<template><div><div v-for="(, key) in obj"></div></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div><div v-for="(, key, index) in obj"></div></div></template>'
+    },
     {
       filename: 'test.vue',
       code: '<template><div><div is="your-component" v-for="x in list" :key="x.id"></div></div></template>'
@@ -183,11 +191,6 @@ tester.run('valid-v-for', rule, {
       code: '<template><div><div v-for></div></div></template>',
       errors: ["'v-for' directives require that attribute value."]
     },
-    {
-      filename: 'test.vue',
-      code: '<template><div><div v-for="(,a,b) in list"></div></div></template>',
-      errors: ["Invalid alias ''."]
-    },
     {
       filename: 'test.vue',
       code: '<template><div><div v-for="(a,,b) in list"></div></div></template>',