feat(nuxt): server-only components (#9972)

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

@@ -210,7 +210,48 @@ This feature only works with Nuxt auto-imports and `#components` imports. Explic
 
 ## .server Components
 
-`.server` components are fallback components of `.client` components.
+`.server` components can either be used on their own or paired with a `.client` component.
+
+### Standalone server components
+
+::StabilityEdge
+
+Standalone server components will always be rendered on the server. When their props update, this will result in a network request that will update the rendered HTML in-place.
+
+Server components are currently experimental and in order to use them, you need to enable the 'component islands' feature in your nuxt.config:
+
+```ts [nuxt.config.ts]
+export default defineNuxtConfig({
+  experimental: {
+    componentIslands: true
+  }
+})
+```
+
+Now you can register server-only components with the `.server` suffix and use them anywhere in your application automatically.
+
+```bash
+| components/
+--| HighlightedMarkdown.server.vue
+```
+
+```html{}[pages/example.vue]
+<template>
+  <div>
+    <!--
+      this will automatically be rendered on the server, meaning your markdown parsing + highlighting
+      libraries are not included in your client bundle.
+     -->
+    <HighlightedMarkdown markdown="# Headline" />
+  </div>
+</template>
+```
+
+::
+
+### 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.
 
 ```bash
 | components/
@@ -227,6 +268,10 @@ This feature only works with Nuxt auto-imports and `#components` imports. Explic
 </template>
 ```
 
+::alert{type=warning}
+It is essential that the client half of the component can 'hydrate' the server-rendered HTML. That is, it should render the same HTML on initial load, or you will experience a hydration mismatch.
+::
+
 ## `<DevOnly>` Component
 
 Nuxt provides the `<DevOnly>` component to render a component only during development.

examples/auto-imports/components/components/ServerOnlyComponent.server.vue

@@ -0,0 +1,21 @@
+<script setup lang="ts">
+const props = defineProps({ foo: Number })
+const colors = [
+  'red',
+  'blue',
+  'yellow'
+]
+const color = colors[(props.foo ?? 1) % colors.length]
+</script>
+
+<template>
+  <section class="flex flex-col gap-1 p-4">
+    I'm a server component with some reactive state: {{ foo }}
+  </section>
+</template>
+
+<style scoped>
+.flex {
+  color: v-bind(color)
+}
+</style>

packages/nuxt/src/components/loader.ts

@@ -1,4 +1,4 @@
-import { pathToFileURL } from 'node:url'
+import { fileURLToPath, pathToFileURL } from 'node:url'
 import { createUnplugin } from 'unplugin'
 import { parseQuery, parseURL } from 'ufo'
 import type { Component, ComponentsOptions } from '@nuxt/schema'
@@ -11,6 +11,7 @@ interface LoaderOptions {
   mode: 'server' | 'client'
   sourcemap?: boolean
   transform?: ComponentsOptions['transform']
+  experimentalComponentIslands?: boolean
 }
 
 function isVueTemplate (id: string) {
@@ -43,6 +44,7 @@ function isVueTemplate (id: string) {
 export const loaderPlugin = createUnplugin((options: LoaderOptions) => {
   const exclude = options.transform?.exclude || []
   const include = options.transform?.include || []
+  const serverComponentRuntime = fileURLToPath(new URL('./runtime/server-component', import.meta.url))
 
   return {
     name: 'nuxt:components-loader',
@@ -65,12 +67,23 @@ export const loaderPlugin = createUnplugin((options: LoaderOptions) => {
       const s = new MagicString(code)
 
       // replace `_resolveComponent("...")` to direct import
-      s.replace(/(?<=[ (])_?resolveComponent\(\s*["'](lazy-|Lazy)?([^'"]*?)["'][\s,]*[^)]*\)/g, (full, lazy, name) => {
+      s.replace(/(?<=[ (])_?resolveComponent\(\s*["'](lazy-|Lazy)?([^'"]*?)["'][\s,]*[^)]*\)/g, (full: string, lazy: string, name: string) => {
         const component = findComponent(components, name, options.mode)
         if (component) {
           let identifier = map.get(component) || `__nuxt_component_${num++}`
           map.set(component, identifier)
 
+          const isServerOnly = component.mode === 'server' &&
+            !components.some(c => c.pascalName === component.pascalName && c.mode === 'client')
+          if (isServerOnly) {
+            imports.add(genImport(serverComponentRuntime, [{ name: 'createServerComponent' }]))
+            imports.add(`const ${identifier} = createServerComponent(${JSON.stringify(name)})`)
+            if (!options.experimentalComponentIslands) {
+              console.warn(`Standalone server components (\`${name}\`) are not yet supported without enabling \`experimental.componentIslands\`.`)
+            }
+            return identifier
+          }
+
           const isClientOnly = component.mode === 'client'
           if (isClientOnly) {
             imports.add(genImport('#app/components/client-only', [{ name: 'createClientOnly' }]))
@@ -114,9 +127,16 @@ export const loaderPlugin = createUnplugin((options: LoaderOptions) => {
 
 function findComponent (components: Component[], name: string, mode: LoaderOptions['mode']) {
   const id = pascalCase(name).replace(/["']/g, '')
+  // Prefer exact match
   const component = components.find(component => id === component.pascalName && ['all', mode, undefined].includes(component.mode))
-  if (!component && components.some(component => id === component.pascalName)) {
-    return components.find(component => component.pascalName === 'ServerPlaceholder')
+  if (component) { return component }
+
+  // Render client-only components on the server with <ServerPlaceholder> (a simple div)
+  if (mode === 'server' && !component) {
+    return components.find(c => c.pascalName === 'ServerPlaceholder')
   }
-  return component
+
+  // Return the other-mode component in all other cases - we'll handle createClientOnly
+  // and createServerComponent above
+  return components.find(component => id === component.pascalName)
 }

packages/nuxt/src/components/module.ts

@@ -196,7 +196,8 @@ export default defineNuxtModule<ComponentsOptions>({
       config.plugins.push(loaderPlugin.vite({
         sourcemap: nuxt.options.sourcemap[mode],
         getComponents,
-        mode
+        mode,
+        experimentalComponentIslands: nuxt.options.experimental.componentIslands
       }))
       if (nuxt.options.experimental.treeshakeClientOnly && isServer) {
         config.plugins.push(TreeShakeTemplatePlugin.vite({
@@ -212,7 +213,8 @@ export default defineNuxtModule<ComponentsOptions>({
         config.plugins.push(loaderPlugin.webpack({
           sourcemap: nuxt.options.sourcemap[mode],
           getComponents,
-          mode
+          mode,
+          experimentalComponentIslands: nuxt.options.experimental.componentIslands
         }))
         if (nuxt.options.experimental.treeshakeClientOnly && mode === 'server') {
           config.plugins.push(TreeShakeTemplatePlugin.webpack({

packages/nuxt/src/components/runtime/server-component.ts

@@ -0,0 +1,16 @@
+import { defineComponent, h } from 'vue'
+// @ts-expect-error virtual import
+import { NuxtIsland } from '#components'
+
+export const createServerComponent = (name: string) => {
+  return defineComponent({
+    name,
+    inheritAttrs: false,
+    setup (_props, { attrs }) {
+      return () => h(NuxtIsland, {
+        name,
+        props: attrs
+      })
+    }
+  })
+}

packages/nuxt/src/components/templates.ts

@@ -86,7 +86,13 @@ export const componentsTemplate: NuxtTemplate<ComponentsTemplateContext> = {
 export const componentsIslandsTemplate: NuxtTemplate<ComponentsTemplateContext> = {
   // components.islands.mjs'
   getContents ({ options }) {
-    return options.getComponents().filter(c => c.island).map(
+    const components = options.getComponents()
+    const islands = components.filter(component =>
+      component.island ||
+      // .server components without a corresponding .client component will need to be rendered as an island
+      (component.mode === 'server' && !components.some(c => c.pascalName === component.pascalName && c.mode === 'client'))
+    )
+    return islands.map(
       (c) => {
         const exp = c.export === 'default' ? 'c.default || c' : `c['${c.export}']`
         const comment = createImportMagicComments(c)

test/basic.test.ts

@@ -57,6 +57,8 @@ describe('pages', () => {
     expect(html).toContain('This is a custom component with a named export.')
     // should apply attributes to client-only components
     expect(html).toContain('<div style="color:red;" class="client-only"></div>')
+    // should render server-only components
+    expect(html).toContain('<div class="server-only" style="background-color:gray;"> server-only component </div>')
     // should register global components automatically
     expect(html).toContain('global component registered automatically')
     expect(html).toContain('global component via suffix')

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

@@ -0,0 +1,5 @@
+<template>
+  <div>
+    server-only component
+  </div>
+</template>

test/fixtures/basic/pages/index.vue

@@ -19,6 +19,7 @@
     <component :is="`test${'-'.toString()}global`" />
     <component :is="`with${'-'.toString()}suffix`" />
     <ClientWrapped ref="clientRef" style="color: red;" class="client-only" />
+    <ServerOnlyComponent class="server-only" style="background-color: gray;" />
   </div>
 </template>