fix(components): [table] selection reference when toggleAllSelection (#16800)

* fix(components): [table] selection is not updated when length is 0

* fix(components): [table] selection reference when toggleAllSelection

* feat: add test

packages/components/table/__tests__/table.test.ts

@@ -790,6 +790,46 @@ describe('Table.vue', () => {
 
       wrapper.unmount()
     })
+
+    it('selection reference', async () => {
+      const wrapper = mount({
+        components: {
+          ElTableColumn,
+          ElTable,
+        },
+        template: `
+          <el-table ref="table" :data="testData" @select-all="handleSelectAll">
+            <el-table-column prop="name" />
+            <el-table-column prop="release" />
+            <el-table-column prop="director" />
+            <el-table-column prop="runtime"/>
+          </el-table>
+        `,
+        data() {
+          return {
+            testData: getTestData(),
+            selection: null,
+          }
+        },
+        methods: {
+          handleSelectAll(selection) {
+            this.selection = selection
+          },
+        },
+      })
+
+      const vm = wrapper.vm
+      vm.$refs.table.toggleAllSelection()
+      await doubleWait()
+      const oldSelection = vm.selection
+      vm.$refs.table.toggleAllSelection()
+      await doubleWait()
+      const newSelection = vm.selection
+      vm.$refs.table.clearSelection()
+      expect(oldSelection !== newSelection).toBe(true)
+      wrapper.unmount()
+    })
+
     it('sort', async () => {
       const wrapper = mount({
         components: {

packages/components/table/src/store/watcher.ts

@@ -155,8 +155,8 @@ function useWatcher<T>() {
   const clearSelection = () => {
     isAllSelected.value = false
     const oldSelection = selection.value
+    selection.value = []
     if (oldSelection.length) {
-      selection.value = []
       instance.emit('selection-change', [])
     }
   }
@@ -238,7 +238,7 @@ function useWatcher<T>() {
         selection.value ? selection.value.slice() : []
       )
     }
-    instance.emit('select-all', selection.value)
+    instance.emit('select-all', (selection.value || []).slice())
   }
 
   const updateSelectionByRowKey = () => {