fix: 解决在组件内定义 input 组件的 placeholder-class 无效的问题

src/core/view/components/input/index.vue

@@ -144,7 +144,7 @@ export default {
   },
   mounted () {
     if (this.confirmType === 'search') {
-      var formElem = document.createElement('form')
+      const formElem = document.createElement('form')
       formElem.action = ''
       formElem.onsubmit = function () {
         return false
@@ -154,6 +154,15 @@ export default {
       this.$refs.wrapper.appendChild(formElem)
     }
 
+    let $vm = this
+    while ($vm) {
+      const scopeId = $vm.$options._scopeId
+      if (scopeId) {
+        this.$refs.placeholder.setAttribute(scopeId, '')
+      }
+      $vm = $vm.$parent
+    }
+
     this.focus && this._focusInput()
   },
   beforeDestroy () {