fix(nuxt): directly render server components (#19605)

docs/2.guide/2.directory-structure/1.components.md

@@ -297,10 +297,6 @@ Now you can register server-only components with the `.server` suffix and use th
 Slots are not supported by server components in their current state of development.
 ::
 
-::alert{type=info}
-Please note that there is a known issue with using async code in a server component. It will lead to a hydration mismatch error on initial render. See [#18500](https://github.com/nuxt/nuxt/issues/18500#issuecomment-1403528142). Until there is a workaround, server-components must be synchronous.
-::
-
 ### Paired with a `.client` component
 
 In this case, the `.server` + `.client` components are two 'halves' of a component and can be used in advanced use cases for separate implementations of a component on server and client side.

packages/nuxt/src/app/components/island-renderer.ts

@@ -1,4 +1,5 @@
-import { createBlock, defineComponent, h, Teleport } from 'vue'
+import type { defineAsyncComponent } from 'vue'
+import { defineComponent, createVNode } from 'vue'
 
 // @ts-ignore
 import * as islandComponents from '#build/components.islands.mjs'
@@ -11,9 +12,8 @@ export default defineComponent({
       required: true
     }
   },
-  async setup (props) {
-    // TODO: https://github.com/vuejs/core/issues/6207
-    const component = islandComponents[props.context.name]
+  setup (props) {
+    const component = islandComponents[props.context.name] as ReturnType<typeof defineAsyncComponent>
 
     if (!component) {
       throw createError({
@@ -21,13 +21,6 @@ export default defineComponent({
         statusMessage: `Island component not found: ${JSON.stringify(component)}`
       })
     }
-
-    if (typeof component === 'object') {
-      await component.__asyncLoader?.()
-    }
-
-    return () => [
-      createBlock(Teleport as any, { to: 'nuxt-island' }, [h(component || 'span', props.context.props)])
-    ]
+    return () => createVNode(component || 'span', props.context.props)
   }
 })

packages/nuxt/src/app/components/nuxt-island.ts

@@ -1,4 +1,4 @@
-import { defineComponent, createStaticVNode, computed, ref, watch } from 'vue'
+import { defineComponent, createStaticVNode, computed, ref, watch, getCurrentInstance } from 'vue'
 import { debounce } from 'perfect-debounce'
 import { hash } from 'ohash'
 import { appendHeader } from 'h3'
@@ -30,10 +30,10 @@ export default defineComponent({
   async setup (props) {
     const nuxtApp = useNuxtApp()
     const hashId = computed(() => hash([props.name, props.props, props.context]))
-
+    const instance = getCurrentInstance()!
     const event = useRequestEvent()
 
-    const html = ref<string>('')
+    const html = ref<string>(process.client ? instance.vnode.el?.outerHTML ?? '<div></div>' : '<div></div>')
     const cHead = ref<Record<'link' | 'style', Array<Record<string, string>>>>({ link: [], style: [] })
     useHead(cHead)
 

packages/nuxt/src/core/runtime/nitro/renderer.ts

@@ -160,6 +160,7 @@ async function getIslandContext (event: H3Event): Promise<NuxtIslandContext> {
 
 const PAYLOAD_CACHE = (process.env.NUXT_PAYLOAD_EXTRACTION && process.env.prerender) ? new Map() : null // TODO: Use LRU cache
 const PAYLOAD_URL_RE = /\/_payload(\.[a-zA-Z0-9]+)?.js(\?.*)?$/
+const ROOT_NODE_REGEX = new RegExp(`^<${appRootTag} id="${appRootId}">([\\s\\S]*)</${appRootTag}>$`)
 
 const PRERENDER_NO_SSR_ROUTES = new Set(['/index.html', '/200.html', '/404.html'])
 
@@ -284,7 +285,7 @@ export default defineRenderHandler(async (event) => {
       renderedMeta.bodyScriptsPrepend,
       ssrContext.teleports?.body
     ]),
-    body: (process.env.NUXT_COMPONENT_ISLANDS && islandContext) ? [] : [_rendered.html],
+    body: [_rendered.html],
     bodyAppend: normalizeChunks([
       process.env.NUXT_NO_SCRIPTS
         ? undefined
@@ -318,7 +319,7 @@ export default defineRenderHandler(async (event) => {
     const islandResponse: NuxtIslandResponse = {
       id: islandContext.id,
       head,
-      html: ssrContext.teleports!['nuxt-island'].replace(/<!--.*-->/g, ''),
+      html: getServerComponentHTML(htmlContext.body),
       state: ssrContext.payload.state
     }
 
@@ -428,3 +429,11 @@ function splitPayload (ssrContext: NuxtSSRContext) {
     payload: { data, prerenderedAt }
   }
 }
+
+/**
+ * remove the root node from the html body
+ */
+function getServerComponentHTML (body: string[]): string {
+  const match = body[0].match(ROOT_NODE_REGEX)
+  return match ? match[1] : body[0]
+}

test/basic.test.ts

@@ -1069,6 +1069,48 @@ describe('component islands', () => {
     `)
   })
 
+  it('render async component', async () => {
+    const result: NuxtIslandResponse = await $fetch(withQuery('/__nuxt_island/LongAsyncComponent', {
+      props: JSON.stringify({
+        count: 3
+      })
+    }))
+    if (isDev()) {
+      result.head.link = result.head.link.filter(l => !l.href.includes('@nuxt+ui-templates'))
+    }
+    expect(result).toMatchInlineSnapshot(`
+      {
+        "head": {
+          "link": [],
+          "style": [],
+        },
+        "html": "<div>that was very long ... <div id=\\"long-async-component-count\\">3</div><p>hello world !!!</p></div>",
+        "state": {},
+      }
+    `)
+  })
+
+  it('render .server async component', async () => {
+    const result: NuxtIslandResponse = await $fetch(withQuery('/__nuxt_island/AsyncServerComponent', {
+      props: JSON.stringify({
+        count: 2
+      })
+    }))
+    if (isDev()) {
+      result.head.link = result.head.link.filter(l => !l.href.includes('@nuxt+ui-templates'))
+    }
+    expect(result).toMatchInlineSnapshot(`
+    {
+      "head": {
+        "link": [],
+        "style": [],
+      },
+      "html": "<div> This is a .server (20ms) async component that was very long ... <div id=\\"async-server-component-count\\">2</div></div>",
+      "state": {},
+    }
+  `)
+  })
+
   it('renders pure components', async () => {
     const result: NuxtIslandResponse = await $fetch(withQuery('/__nuxt_island/PureComponent', {
       props: JSON.stringify({

test/fixtures/basic/components/AsyncServerComponent.server.vue

@@ -0,0 +1,17 @@
+<template>
+  <div>
+    This is a .server (20ms) async component
+    {{ data }}
+    <div id="async-server-component-count">
+      {{ count }}
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+defineProps<{
+  count: number
+}>()
+
+const { data } = await useFetch('/api/very-long-request')
+</script>

test/fixtures/basic/components/islands/LongAsyncComponent.vue

@@ -0,0 +1,17 @@
+<template>
+  <div>
+    {{ data }}
+    <div id="long-async-component-count">
+      {{ count }}
+    </div>
+    <p>hello world !!!</p>
+  </div>
+</template>
+
+<script setup lang="ts">
+defineProps<{
+  count: number
+}>()
+
+const { data } = await useFetch('/api/very-long-request')
+</script>

test/fixtures/basic/pages/islands.vue

@@ -7,6 +7,8 @@ const islandProps = ref({
 })
 
 const routeIslandVisible = ref(false)
+
+const count = ref(0)
 </script>
 
 <template>
@@ -27,6 +29,16 @@ const routeIslandVisible = ref(false)
     <button v-else @click="routeIslandVisible = true">
       Show
     </button>
+
+    <p>async .server component</p>
+    <AsyncServerComponent :count="count" />
+    <div>
+      Async island component (20ms):
+      <NuxtIsland name="LongAsyncComponent" :props="{ count }" />
+      <button @click="count++">
+        add +1 to count
+      </button>
+    </div>
   </div>
 </template>
 

test/fixtures/basic/server/api/very-long-request.ts

@@ -0,0 +1,7 @@
+export default defineEventHandler(async () => {
+  await timeout(20)
+  return 'that was very long ...'
+})
+function timeout (ms: number) {
+  return new Promise(resolve => setTimeout(resolve, ms))
+}