fix: siderbar 已展开菜单再次点击时不展开的bug

docs/.vuepress/theme/components/SidebarLinks.vue

+<template>
+  <ul
+    v-if="items.length"
+    class="sidebar-links"
+  >
+    <li
+      v-for="(item, i) in items"
+      :key="i"
+    >
+      <SidebarGroup
+        v-if="item.type === 'group'"
+        :item="item"
+        :open="i === openGroupIndex"
+        :collapsable="item.collapsable || item.collapsible"
+        :depth="depth"
+        @toggle="toggleGroup(i)"
+      />
+      <SidebarLink
+        v-else
+        :sidebar-depth="sidebarDepth"
+        :item="item"
+      />
+    </li>
+  </ul>
+</template>
+
+<script>
+import SidebarGroup from '@theme/components/SidebarGroup.vue'
+import SidebarLink from '@theme/components/SidebarLink.vue'
+import { isActive, debounce } from '../util'
+
+export default {
+  name: 'SidebarLinks',
+
+  components: { SidebarGroup, SidebarLink },
+
+  props: [
+    'items',
+    'depth',  // depth of current sidebar links
+    'sidebarDepth', // depth of headers to be extracted
+    'initialOpenGroupIndex'
+  ],
+
+  data () {
+    return {
+      openGroupIndex: this.initialOpenGroupIndex || 0
+    }
+  },
+
+  watch: {
+    '$route': debounce(function () {
+      this.refreshIndex()
+    })
+  },
+
+  created () {
+    this.refreshIndex()
+  },
+
+  methods: {
+    refreshIndex () {
+      const index = resolveOpenGroupIndex(
+        this.$route,
+        this.items
+      )
+      if (index > -1) {
+        this.openGroupIndex = index
+      }
+    },
+
+    toggleGroup (index) {
+      this.openGroupIndex = index === this.openGroupIndex ? -1 : index
+    },
+
+    isActive (page) {
+      return isActive(this.$route, page.regularPath)
+    }
+  }
+}
+
+function resolveOpenGroupIndex (route, items) {
+  for (let i = 0; i < items.length; i++) {
+    const item = items[i]
+    if (descendantIsActive(route, item)) {
+      return i
+    }
+  }
+  return -1
+}
+
+function descendantIsActive (route, item) {
+  if (item.type === 'group') {
+    const childIsActive = item.path && isActive(route, item.path)
+    const grandChildIsActive = item.children.some(child => {
+      if (child.type === 'group') {
+        return descendantIsActive(route, child)
+      } else {
+        return child.type === 'page' && isActive(route, child.path)
+      }
+    })
+
+    return childIsActive || grandChildIsActive
+  }
+  return false
+}
+</script>