fix(date-picker): when default slot is a comment node, date-picker will not display (#4105)

Author: meteor199

components/_util/props-util/index.js

@@ -341,6 +341,10 @@ export function isEmptyElement(c) {
   );
 }
 
+export function isEmptySlot(c) {
+  return !c || c().every(isEmptyElement);
+}
+
 export function isStringElement(c) {
   return c && c.type === Text;
 }

components/date-picker/createPicker.tsx

@@ -14,6 +14,7 @@ import { hasProp, getOptionProps, getComponent, isValidElement } from '../_util/
 import { cloneElement } from '../_util/vnode';
 import { formatDate } from './utils';
 import { getDataAndAriaProps } from '../_util/util';
+import { isEmptySlot } from '../_util/props-util';
 
 export interface PickerProps {
   value?: moment.Moment;
@@ -255,7 +256,7 @@ export default function createPicker<P>(
         >
           <VcDatePicker
             {...vcDatePickerProps}
-            v-slots={{ default: input, ...$slots }}
+            v-slots={{ ...$slots, default: isEmptySlot($slots.default) ? input : $slots.default }}
           ></VcDatePicker>
         </span>
       );