From ba81e21906df6450d4a742e36ffd172cb7fbaf4a Mon Sep 17 00:00:00 2001
From: MATILLAT Quentin <qmatillat@gmail.com>
Date: Tue, 27 Dec 2022 16:26:17 +0100
Subject: [PATCH] feat(VList): add lazy mode to VListGroup

Add a `lazy` props to skip the rendering of children if the group has never
been opened

This allow to render instantly a list with ~1k elements (see example in docs)
---
 .../examples/v-list/misc-lazy-rendering.vue   | 68 ++++++++++++++
 .../docs/src/pages/en/components/lists.md     | 26 ++----
 .../src/components/VList/VListGroup.tsx       | 88 +++++++++++--------
 .../VList/__tests__/VListGroup.spec.cy.tsx    | 58 ++++++++----
 4 files changed, 168 insertions(+), 72 deletions(-)
 create mode 100644 packages/docs/src/examples/v-list/misc-lazy-rendering.vue

diff --git a/packages/docs/src/examples/v-list/misc-lazy-rendering.vue b/packages/docs/src/examples/v-list/misc-lazy-rendering.vue
new file mode 100644
index 00000000000..35fcb074e1a
--- /dev/null
+++ b/packages/docs/src/examples/v-list/misc-lazy-rendering.vue
@@ -0,0 +1,68 @@
+<template>
+  <v-card>
+    <v-card-title>List with {{ size }} elements</v-card-title>
+
+    <v-card-text v-if="data">
+      <v-list>
+        <recursive-list :entry="data"></recursive-list>
+      </v-list>
+    </v-card-text>
+    <v-card-actions v-else class="justify-center">
+      <v-btn @click="data = MakeEntries()">Prepare</v-btn>
+    </v-card-actions>
+  </v-card>
+</template>
+
+<script lang="ts" setup>
+  import { computed, h, ref, VNode } from 'vue'
+  import { VListGroup, VListItem } from 'vuetify/components'
+
+  export type Entry = {
+    name: string,
+    children?: Entry[],
+  }
+
+  /*
+  <VListGroup v-if="entry.children" lazy>
+    <template v-slot:activator="{ props }">
+      <VListItem v-bind="props">
+        {{ p.val.name }}
+      </VListItem>
+    </template>
+
+    <RecursiveList :val="e" v-for="e in p.val.children" />
+  </VListGroup>
+
+  <VListItem v-else>
+    {{ p.val.name }}
+  </VListItem>
+  */
+  const RecursiveList = ({ entry }: { entry: Entry }): VNode =>
+    entry.children
+      ? h(VListGroup, { lazy: true }, {
+        default: () => entry.children?.map(entry => RecursiveList({ entry })),
+        activator: ({ props }: any) => h(VListItem, props, { default: () => entry.name }),
+      })
+      : h(VListItem, null, { default: () => entry.name })
+
+  function MakeEntries (prefix = 'Prop', depth = 5): Entry {
+    let children
+
+    if (depth > 0) {
+      children = []
+
+      for (let i = 0; i < 5; ++i) {
+        children.push(MakeEntries(prefix + '.' + i, depth - 1))
+      }
+    }
+
+    return { name: prefix, children }
+  }
+
+  function GetSize (v: Entry): number {
+    return v.children?.map(GetSize).reduce((acc, v) => acc + v, 1) ?? 1
+  }
+
+  const data = ref<Entry>()
+  const size = computed(() => data.value ? GetSize(data.value) : 0)
+</script>
diff --git a/packages/docs/src/pages/en/components/lists.md b/packages/docs/src/pages/en/components/lists.md
index e660967f2f6..bda8dbd131d 100644
--- a/packages/docs/src/pages/en/components/lists.md
+++ b/packages/docs/src/pages/en/components/lists.md
@@ -6,37 +6,23 @@ meta:
   keywords: lists, vuetify list component, vue list component
 related:
   - /components/item-groups/
-  - /components/avatars/
-  - /components/sheets/
 ---
 
 # Lists
 
 The `v-list` component is used to display information. It can contain an avatar, content, actions, subheaders and much more. Lists present content in a way that makes it easy to identify a specific item in a collection. They provide a consistent styling for organizing groups of text and images.
 
+<entry />
+
 ## Usage
 
 Lists come in three main variations. **single-line** (default), **two-line** and **three-line**. The line declaration specifies the minimum height of the item and can also be controlled from `v-list` with the same prop.
 
 <usage name="v-list" />
 
-<entry />
-
 ## API
 
-| Component | Description |
-| - | - |
-| [v-list](/api/v-list/) | Primary Component |
-| [v-list-group](/api/v-list-group/) | Sub-component used to display or hide groups of items |
-| [v-list-subheader](/api/v-list-subheader/) | Sub-component used to separate groups of items |
-| [v-list-item](/api/v-list-item/) | Sub-component used to display a single item or modify the `v-list` state |
-| [v-list-item-title](/api/v-list-item-title/) | Sub-component used to display the title of a list item. Wraps the `#title` slot |
-| [v-list-item-subtitle](/api/v-list-item-subtitle/) | Sub-component used to display the subtitle of a list item. Wraps the `#subtitle` slot |
-| [v-list-item-action](/api/v-list-item-action/) | Sub-component used to display [v-checkbox](/components/checkboxes/) or [v-switch](/components/switches/) |
-| [v-list-img](/api/v-list-img/) | Sub-component that is used to wrap a the [v-img](/components/images/) component |
-| [v-list-item-media](/api/v-list-item-media/) | Sub-component that is used to wrap a the [v-img](/components/images/) component |
-
-<api-inline hide-links />
+<api-inline />
 
 ## Examples
 
@@ -125,3 +111,9 @@ Lists can contain subheaders, dividers, and can contain 1 or more lines. The sub
 A **three-line** list with actions. Utilizing **v-list-group**, easily connect actions to your tiles.
 
 <example file="v-list/misc-action-and-item-groups" />
+
+#### Lazy rendering
+
+A big list rendered instantly using *lazy* option.
+
+<example file="v-list/misc-lazy-rendering" />
diff --git a/packages/vuetify/src/components/VList/VListGroup.tsx b/packages/vuetify/src/components/VList/VListGroup.tsx
index 2651e3491cb..f80934d778b 100644
--- a/packages/vuetify/src/components/VList/VListGroup.tsx
+++ b/packages/vuetify/src/components/VList/VListGroup.tsx
@@ -3,21 +3,26 @@ import { VDefaultsProvider } from '@/components/VDefaultsProvider'
 import { VExpandTransition } from '@/components/transitions'
 
 // Composables
+import { useList } from './list'
 import { IconValue } from '@/composables/icons'
-import { makeComponentProps } from '@/composables/component'
+import { makeLazyProps, useLazy } from '@/composables/lazy'
 import { makeTagProps } from '@/composables/tag'
-import { MaybeTransition } from '@/composables/transition'
-import { useList } from './list'
 import { useNestedGroupActivator, useNestedItem } from '@/composables/nested/nested'
-import { useSsrBoot } from '@/composables/ssrBoot'
 
 // Utilities
 import { computed, toRef } from 'vue'
-import { defineComponent, genericComponent, propsFactory, useRender } from '@/util'
-
-export type VListGroupSlots = {
-  default: []
-  activator: [{ isOpen: boolean, props: Record<string, unknown> }]
+import { defineComponent, genericComponent, pick, propsFactory, useRender } from '@/util'
+
+// Types
+import type { InternalListItem } from './VList'
+import type { SlotsToProps } from '@/util'
+import type { ExtractPropTypes, Ref } from 'vue'
+
+export type ListGroupActivatorSlot = {
+  props: {
+    onClick: (e: Event) => void
+    class: string
+  }
 }
 
 const VListGroupActivator = defineComponent({
@@ -31,9 +36,7 @@ const VListGroupActivator = defineComponent({
 })
 
 export const makeVListGroupProps = propsFactory({
-  /* @deprecated */
   activeColor: String,
-  baseColor: String,
   color: String,
   collapseIcon: {
     type: IconValue,
@@ -47,47 +50,46 @@ export const makeVListGroupProps = propsFactory({
   appendIcon: IconValue,
   fluid: Boolean,
   subgroup: Boolean,
-  title: String,
   value: null,
 
-  ...makeComponentProps(),
+  ...makeLazyProps(),
   ...makeTagProps(),
 }, 'v-list-group')
 
-export const VListGroup = genericComponent<VListGroupSlots>()({
+export const VListGroup = genericComponent<new <T extends InternalListItem>() => {
+  $props: {
+    items?: T[]
+  } & SlotsToProps<{
+    activator: [ListGroupActivatorSlot]
+    default: []
+  }>
+}>()({
   name: 'VListGroup',
 
-  props: makeVListGroupProps(),
+  props: {
+    title: String,
+
+    ...makeVListGroupProps(),
+  },
 
   setup (props, { slots }) {
     const { isOpen, open, id: _id } = useNestedItem(toRef(props, 'value'), true)
     const id = computed(() => `v-list-group--id-${String(_id.value)}`)
     const list = useList()
-    const { isBooted } = useSsrBoot()
+
+    const { hasContent, onAfterLeave } = useLazy(props, isOpen)
 
     function onClick (e: Event) {
       open(!isOpen.value, e)
     }
 
-    const activatorProps = computed(() => ({
+    const activatorProps: Ref<ListGroupActivatorSlot['props']> = computed(() => ({
       onClick,
       class: 'v-list-group__header',
       id: id.value,
     }))
 
     const toggleIcon = computed(() => isOpen.value ? props.collapseIcon : props.expandIcon)
-    const activatorDefaults = computed(() => ({
-      VListItem: {
-        active: isOpen.value,
-        activeColor: props.activeColor,
-        baseColor: props.baseColor,
-        color: props.color,
-        prependIcon: props.prependIcon || (props.subgroup && toggleIcon.value),
-        appendIcon: props.appendIcon || (!props.subgroup && toggleIcon.value),
-        title: props.title,
-        value: props.value,
-      },
-    }))
 
     useRender(() => (
       <props.tag
@@ -99,23 +101,33 @@ export const VListGroup = genericComponent<VListGroupSlots>()({
             'v-list-group--subgroup': props.subgroup,
             'v-list-group--open': isOpen.value,
           },
-          props.class,
         ]}
-        style={ props.style }
       >
         { slots.activator && (
-          <VDefaultsProvider defaults={ activatorDefaults.value }>
+          <VDefaultsProvider
+            defaults={{
+              VListItem: {
+                active: isOpen.value,
+                activeColor: props.activeColor,
+                color: props.color,
+                prependIcon: props.prependIcon || (props.subgroup && toggleIcon.value),
+                appendIcon: props.appendIcon || (!props.subgroup && toggleIcon.value),
+                title: props.title,
+                value: props.value,
+              },
+            }}
+          >
             <VListGroupActivator>
-              { slots.activator({ props: activatorProps.value, isOpen: isOpen.value }) }
+              { slots.activator({ props: activatorProps.value, isOpen }) }
             </VListGroupActivator>
           </VDefaultsProvider>
         )}
 
-        <MaybeTransition transition={{ component: VExpandTransition }} disabled={ !isBooted.value }>
+        <VExpandTransition onAfterLeave={ onAfterLeave }>
           <div class="v-list-group__items" role="group" aria-labelledby={ id.value } v-show={ isOpen.value }>
-            { slots.default?.() }
+            { hasContent.value && slots.default?.() }
           </div>
-        </MaybeTransition>
+        </VExpandTransition>
       </props.tag>
     ))
 
@@ -124,3 +136,7 @@ export const VListGroup = genericComponent<VListGroupSlots>()({
 })
 
 export type VListGroup = InstanceType<typeof VListGroup>
+
+export function filterListGroupProps (props: ExtractPropTypes<ReturnType<typeof makeVListGroupProps>>) {
+  return pick(props, Object.keys(VListGroup.props) as any)
+}
diff --git a/packages/vuetify/src/components/VList/__tests__/VListGroup.spec.cy.tsx b/packages/vuetify/src/components/VList/__tests__/VListGroup.spec.cy.tsx
index 89535931f7a..0cfcde97c87 100644
--- a/packages/vuetify/src/components/VList/__tests__/VListGroup.spec.cy.tsx
+++ b/packages/vuetify/src/components/VList/__tests__/VListGroup.spec.cy.tsx
@@ -5,6 +5,28 @@ import { VListGroup } from '../VListGroup'
 import { VListItem } from '../VListItem'
 import { VList } from '../VList'
 
+function ListGroup (lazy: boolean, open: boolean): JSX.Element {
+  return (
+    <CenteredGrid width="200px">
+      <h2 class="mt-8">ListGroup</h2>
+
+      <VList opened={ open ? ['group'] : [] }>
+        <VListGroup value="group" lazy={ lazy }>
+          {{
+            activator: ({ props }) => <VListItem { ...props } title="Group" />,
+            default: () => (
+              <>
+                <VListItem title="Child 1" />
+                <VListItem title="Child 2" />
+              </>
+            ),
+          }}
+        </VListGroup>
+      </VList>
+    </CenteredGrid>
+  )
+}
+
 describe('VListGroup', () => {
   function mountFunction (content: JSX.Element) {
     return cy.mount(() => content)
@@ -27,26 +49,24 @@ describe('VListGroup', () => {
   })
 
   it('supports children', () => {
-    const wrapper = mountFunction((
-      <CenteredGrid width="200px">
-        <h2 class="mt-8">ListGroup</h2>
+    const wrapper = mountFunction(ListGroup(false, true))
+    wrapper.get('.v-list-item-title').contains('Group')
+  })
 
-        <VList opened={['group']}>
-          <VListGroup value="group">
-            {{
-              activator: props => <VListItem { ...props } title="Group" />,
-              default: () => (
-                <>
-                  <VListItem title="Child 1" />
-                  <VListItem title="Child 2" />
-                </>
-              ),
-            }}
-          </VListGroup>
-        </VList>
-      </CenteredGrid>
-    ))
+  describe('lazy', () => {
+    it('open on click', () => {
+      const wrapper = mountFunction(ListGroup(true, false))
 
-    wrapper.get('.v-list-item-title').contains('Group')
+      const group = wrapper.get('.v-list-group')
+      group.get('.v-list-group__items .v-list-item').should('have.length', 0)
+      group.get('.v-list-item').click()
+      group.get('.v-list-group__items .v-list-item').should('have.length', 2)
+    })
+
+    it('already opened children', () => {
+      const wrapper = mountFunction(ListGroup(true, true))
+
+      wrapper.get('.v-list-group__items .v-list-item').should('have.length', 2)
+    })
   })
 })