feat: experimental feature switchLocalePathLinkSSR with <SwitchLocalePathLink> component

docs/content/docs/2.guide/8.lang-switcher.md

@@ -77,10 +77,13 @@ Dealing with dynamic route parameters requires a bit more work because you need
 During SSR it matters when and where you set i18n parameters, since there is no reactivity during SSR.
 
 :br :br
-Components which have already been rendered do not update by changes introduced by pages and components further down the tree. Instead, these links are updated on the client side, so this should not cause any issues.
+Components which have already been rendered do not update by changes introduced by pages and components further down the tree. Instead, these links are updated on the client side during hydration, in most cases this should not cause issues.
 
 :br :br
 This is not the case for SEO tags, these are updated correctly during SSR regardless of when and where i18n parameters are set.
+
+:br :br
+Check out the experimental [`switchLocalePathLinkSSR`](/docs/options/misc#experimental) feature, which combined with the [`<SwitchLocalePathLink>`](/docs/api/components#switchlocalepathlink) component, correctly renders links during SSR regardless of where and when it is used. 
 ::
 
 An example (replace `slug` with the applicable route parameter):

docs/content/docs/3.options/10.misc.md

@@ -6,15 +6,16 @@ description: Miscellaneous options.
 ## `experimental`
 
 - type: `object`
-- default: `{ localeDetector: '' }`
+- default: `{ localeDetector: '', switchLocalePathLinkSSR: false }`
 
 Supported properties:
 
 - `localeDetector` (default: `''`) - Specify the locale detector to be called per request on the server side. You need to specify the filepath where the locale detector is defined.
-
 ::callout{type="warning"}
 About how to define the locale detector, see the [`defineI18nLocaleDetector` API](/docs/api#definei18nlocaledetector)
 ::
+- `switchLocalePathLinkSSR` (default: `false`) - Changes the way dynamic route parameters are tracked and updated internally, improving language switcher SSR when using the [`SwitchLocalePathLink`](/docs/api/components#switchlocalepathlink) component.
+
 
 ## `customBlocks`
 

docs/content/docs/4.api/2.components.md

@@ -52,3 +52,40 @@ This component supports all [props documented for `<NuxtLink>`](https://nuxt.com
 | Prop     | Description                                                                                                                                  |
 | -------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
 | `locale` | Optional prop to force localization using passed Locale, it defaults to the current locale. Identical to `locale` argument of `localePath()` |
+
+
+## `<SwitchLocalePathLink>`
+
+This component acts as a constrained [`<NuxtLink>`](https://nuxt.com/docs/api/components/nuxt-link#nuxtlink) which internally uses `switchLocalePath` to link to the same page in the provided locale.
+
+With [`experimental.switchLocalePathLinkSSR`](/docs/options/misc#experimental) enabled, this component will correctly render dynamic route parameters during server-side rendering.
+
+### Examples
+
+#### Basic usage
+
+```vue
+<template>
+  <SwitchLocalePathLink locale="nl">Dutch</SwitchLocalePathLink>
+  <SwitchLocalePathLink locale="en">English</SwitchLocalePathLink>
+</template>
+
+<!-- equivalent to -->
+
+<script setup>
+const switchLocalePath = useSwitchLocalePath()
+</script>
+
+<template>
+  <NuxtLink :to="switchLocalePath('nl')">Dutch</NuxtLink>
+  <NuxtLink :to="switchLocalePath('en')">English</NuxtLink>
+</template>
+```
+
+### Props
+
+This component supports most, but not all [props documented for `<NuxtLink>`](https://nuxt.com/docs/api/components/nuxt-link#props) (does not support `to` or `href`) in addition to props described below.
+
+| Prop     | Description                                                                                                                                  |
+| -------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
+| `locale` | Optional prop to force localization using passed Locale, it defaults to the current locale. Identical to `locale` argument of `switchLocalePath()` |

playground/layouts/default.vue

@@ -1,6 +1,5 @@
 <script setup lang="ts">
-import { useSetI18nParams, useLocaleHead } from '#i18n'
-import { useHead } from '#imports'
+import { useLocaleHead } from '#i18n'
 
 const route = useRoute()
 const { t } = useI18n()

playground/nuxt.config.ts

@@ -107,7 +107,8 @@ export default defineNuxtConfig({
   // debug: true,
   i18n: {
     experimental: {
-      localeDetector: './localeDetector.ts'
+      localeDetector: './localeDetector.ts',
+      switchLocalePathLinkSSR: true
     },
     compilation: {
       // jit: false,

playground/pages/products.vue

@@ -1,7 +1,6 @@
 <script lang="ts" setup>
 const { locale, locales } = useI18n()
 const localePath = useLocalePath()
-const switchLocalePath = useSwitchLocalePath()
 
 const { data } = await useAsyncData('products', () => $fetch(`/api/products`))
 definePageMeta({
@@ -21,7 +20,7 @@ definePageMeta({
   <div>
     <nav style="padding: 1em">
       <span v-for="locale in locales" :key="locale.code">
-        <NuxtLink :to="switchLocalePath(locale.code) || ''">{{ locale.name }}</NuxtLink> |
+        <SwitchLocalePathLink :locale="locale.code">{{ locale.name }}</SwitchLocalePathLink> |
       </span>
     </nav>
     <NuxtLink

specs/experimental/switch_locale_path_link_ssr.spec.ts

@@ -0,0 +1,58 @@
+import { test, expect } from 'vitest'
+import { fileURLToPath } from 'node:url'
+import { $fetch, setup } from '../utils'
+import { getDom, gotoPath, renderPage, waitForURL } from '../helper'
+
+await setup({
+  rootDir: fileURLToPath(new URL(`../fixtures/basic_usage`, import.meta.url)),
+  browser: true,
+  // prerender: true,
+  // overrides
+  nuxtConfig: {
+    runtimeConfig: {
+      public: {
+        i18n: {
+          baseUrl: ''
+        }
+      }
+    },
+    i18n: {
+      experimental: {
+        switchLocalePathLinkSSR: true
+      }
+    }
+  }
+})
+
+describe('experimental.switchLocalePathLinkSSR', async () => {
+  test('dynamic parameters render and update reactively client-side', async () => {
+    const { page } = await renderPage('/products/big-chair')
+
+    expect(await page.locator('#switch-locale-path-link-nl').getAttribute('href')).toEqual('/nl/products/grote-stoel')
+
+    await gotoPath(page, '/nl/products/rode-mok')
+    expect(await page.locator('#switch-locale-path-link-en').getAttribute('href')).toEqual('/products/red-mug')
+
+    // Translated params are not lost on query changes
+    await page.locator('#params-add-query').click()
+    await waitForURL(page, '/nl/products/rode-mok?test=123')
+    expect(await page.locator('#switch-locale-path-link-en').getAttribute('href')).toEqual('/products/red-mug?test=123')
+
+    await page.locator('#params-remove-query').click()
+    await waitForURL(page, '/nl/products/rode-mok')
+    expect(await page.locator('#switch-locale-path-link-en').getAttribute('href')).toEqual('/products/red-mug')
+  })
+
+  test('dynamic parameters rendered correctly during SSR', async () => {
+    // head tags - alt links are updated server side
+    const product1Html = await $fetch('/products/big-chair')
+    const product1Dom = getDom(product1Html)
+    expect(product1Dom.querySelector('#i18n-alt-nl').href).toEqual('/nl/products/grote-stoel')
+    expect(product1Dom.querySelector('#switch-locale-path-link-nl').href).toEqual('/nl/products/grote-stoel')
+
+    const product2Html = await $fetch('/nl/products/rode-mok')
+    const product2dom = getDom(product2Html)
+    expect(product2dom.querySelector('#i18n-alt-en').href).toEqual('/products/red-mug')
+    expect(product2dom.querySelector('#switch-locale-path-link-en').href).toEqual('/products/red-mug')
+  })
+})

specs/fixtures/basic_usage/components/LangSwitcher.vue

@@ -25,6 +25,18 @@ const localesExcludingCurrent = computed(() => {
         >{{ locale.name }}</NuxtLink
       >
     </section>
+    <section id="lang-switcher-with-switch-locale-path-link">
+      <strong>Using <code>SwitchLocalePathLink</code></strong
+      >:
+      <SwitchLocalePathLink
+        v-for="(locale, index) in localesExcludingCurrent"
+        :id="`switch-locale-path-link-${locale.code}`"
+        :key="index"
+        :exact="true"
+        :locale="locale.code"
+        >{{ locale.name }}</SwitchLocalePathLink
+      >
+    </section>
     <section id="lang-switcher-with-set-locale">
       <strong>Using <code>setLocale()</code></strong
       >:

src/constants.ts

@@ -24,10 +24,12 @@ export const STRATEGIES = {
 
 export const DEFAULT_DYNAMIC_PARAMS_KEY = 'nuxtI18n'
 export const DEFAULT_COOKIE_KEY = 'i18n_redirected'
+export const SWITCH_LOCALE_PATH_LINK_IDENTIFIER = 'nuxt-i18n-slp'
 
 export const DEFAULT_OPTIONS = {
   experimental: {
-    localeDetector: ''
+    localeDetector: '',
+    switchLocalePathLinkSSR: false
   },
   bundle: {
     compositionOnly: true,

src/module.ts

@@ -165,7 +165,8 @@ export default defineNuxtModule<NuxtI18nOptions>({
         },
         {} as Record<string, { domain: string | undefined }>
       ),
-      detectBrowserLanguage: options.detectBrowserLanguage ?? DEFAULT_OPTIONS.detectBrowserLanguage
+      detectBrowserLanguage: options.detectBrowserLanguage ?? DEFAULT_OPTIONS.detectBrowserLanguage,
+      experimental: options.experimental
       // TODO: we should support more i18n module options. welcome PRs :-)
     })
 
@@ -308,6 +309,11 @@ export default defineNuxtModule<NuxtI18nOptions>({
       filePath: resolve(runtimeDir, 'components/NuxtLinkLocale')
     })
 
+    await addComponent({
+      name: 'SwitchLocalePathLink',
+      filePath: resolve(runtimeDir, 'components/SwitchLocalePathLink')
+    })
+
     await addImports([
       { name: 'useI18n', from: vueI18nPath },
       ...[
@@ -356,6 +362,12 @@ export interface ModulePublicRuntimeConfig {
     baseUrl: NuxtI18nOptions['baseUrl']
     rootRedirect: NuxtI18nOptions['rootRedirect']
 
+    /**
+     * Overwritten at build time, used to pass generated options to runtime
+     *
+     * @internal
+     */
+    experimental: NonNullable<NuxtI18nOptions['experimental']>
     /**
      * Overwritten at build time, used to pass generated options to runtime
      *

src/options.d.ts

@@ -28,5 +28,6 @@ export const parallelPlugin: boolean
 export const NUXT_I18N_MODULE_ID = ''
 export const DEFAULT_DYNAMIC_PARAMS_KEY: string
 export const DEFAULT_COOKIE_KEY: string
+export const SWITCH_LOCALE_PATH_LINK_IDENTIFIER: string
 
 export { NuxtI18nOptions, DetectBrowserLanguageOptions, RootRedirectOptions } from './types'

src/runtime/components/SwitchLocalePathLink.ts

@@ -0,0 +1,28 @@
+import { SWITCH_LOCALE_PATH_LINK_IDENTIFIER } from '#build/i18n.options.mjs'
+import { useSwitchLocalePath } from '#i18n'
+import { defineNuxtLink } from '#imports'
+import { Comment, defineComponent, h } from 'vue'
+
+import type { PropType } from 'vue'
+
+const NuxtLink = defineNuxtLink({ componentName: 'NuxtLink' })
+
+export default defineComponent({
+  name: 'SwitchLocalePathLink',
+  props: {
+    locale: {
+      type: String as PropType<string>,
+      required: true
+    }
+  },
+  inheritAttrs: false,
+  setup(props, { slots, attrs }) {
+    const switchLocalePath = useSwitchLocalePath()
+
+    return () => [
+      h(Comment, `${SWITCH_LOCALE_PATH_LINK_IDENTIFIER}-[${props.locale}]`),
+      h(NuxtLink, { ...attrs, to: switchLocalePath(props.locale) }, slots.default),
+      h(Comment, `/${SWITCH_LOCALE_PATH_LINK_IDENTIFIER}`)
+    ]
+  }
+})

src/runtime/composables/index.ts

@@ -47,12 +47,14 @@ export function useSetI18nParams(seoAttributes?: SeoAttributesOptions): SetI18nP
   const locale = getLocale(i18n)
   const locales = getNormalizedLocales(getLocales(i18n))
   const _i18nParams = ref({})
+  const experimentalSSR = common.runtimeConfig.public.i18n.experimental.switchLocalePathLinkSSR
 
   const i18nParams = computed({
     get() {
-      return router.currentRoute.value.meta.nuxtI18n ?? {}
+      return experimentalSSR ? common.metaState.value : router.currentRoute.value.meta.nuxtI18n ?? {}
     },
     set(val) {
+      common.metaState.value = val
       _i18nParams.value = val
       router.currentRoute.value.meta.nuxtI18n = val
     }
@@ -61,7 +63,7 @@ export function useSetI18nParams(seoAttributes?: SeoAttributesOptions): SetI18nP
   const stop = watch(
     () => router.currentRoute.value.fullPath,
     () => {
-      router.currentRoute.value.meta.nuxtI18n = _i18nParams.value
+      router.currentRoute.value.meta.nuxtI18n = experimentalSSR ? common.metaState.value : _i18nParams.value
     }
   )
 

src/runtime/plugins/i18n.ts

@@ -7,9 +7,11 @@ import {
   isSSG,
   localeLoaders,
   parallelPlugin,
-  normalizedLocales
+  normalizedLocales,
+  SWITCH_LOCALE_PATH_LINK_IDENTIFIER
 } from '#build/i18n.options.mjs'
 import { loadVueI18nOptions, loadInitialMessages, loadLocale } from '../messages'
+import { useSwitchLocalePath } from '../composables'
 import {
   loadAndSetLocale,
   detectLocale,
@@ -391,6 +393,29 @@ export default defineNuxtPlugin({
     // inject for nuxt helpers
     injectNuxtHelpers(nuxtContext, i18n)
 
+    // Replace `SwitchLocalePathLink` href in rendered html for SSR support
+    if (runtimeI18n.experimental.switchLocalePathLinkSSR === true) {
+      const switchLocalePath = useSwitchLocalePath()
+
+      const switchLocalePathLinkWrapperExpr = new RegExp(
+        [
+          `<!--${SWITCH_LOCALE_PATH_LINK_IDENTIFIER}-\\[(\\w+)\\]-->`,
+          `.+?`,
+          `<!--\/${SWITCH_LOCALE_PATH_LINK_IDENTIFIER}-->`
+        ].join(''),
+        'g'
+      )
+
+      nuxt.hook('app:rendered', ctx => {
+        if (ctx.renderResult?.html == null) return
+
+        ctx.renderResult.html = ctx.renderResult.html.replaceAll(
+          switchLocalePathLinkWrapperExpr,
+          (match: string, p1: string) => match.replace(/href="([^"]+)"/, `href="${switchLocalePath(p1 ?? '')}"`)
+        )
+      })
+    }
+
     let routeChangeCount = 0
 
     addRouteMiddleware(

src/runtime/routing/compatibles/routing.ts

@@ -218,8 +218,13 @@ export function resolveRoute(common: CommonComposableOptions, route: RouteLocati
 export const DefaultSwitchLocalePathIntercepter: SwitchLocalePathIntercepter = (path: string) => path
 
 function getLocalizableMetaFromDynamicParams(
+  common: CommonComposableOptions,
   route: RouteLocationNormalizedLoaded
 ): Record<Locale, Record<string, unknown>> {
+  if (common.runtimeConfig.public.i18n.experimental.switchLocalePathLinkSSR) {
+    return unref(common.metaState.value) as Record<Locale, any>
+  }
+
   const meta = route.meta || {}
   return (unref(meta)?.[DEFAULT_DYNAMIC_PARAMS_KEY] || {}) as Record<Locale, any>
 }
@@ -247,7 +252,7 @@ export function switchLocalePath(
 
   const switchLocalePathIntercepter = extendSwitchLocalePathIntercepter(common.runtimeConfig)
   const routeCopy = routeToObject(route)
-  const resolvedParams = getLocalizableMetaFromDynamicParams(route)[locale]
+  const resolvedParams = getLocalizableMetaFromDynamicParams(common, route)[locale]
 
   const baseRoute = { ...routeCopy, name, params: { ...routeCopy.params, ...resolvedParams } }
   const path = localePath(common, baseRoute, locale)

src/runtime/utils.ts

@@ -38,6 +38,7 @@ import { getLocale, setLocale, getLocaleCodes, getI18nTarget } from './routing/u
 
 import type { I18n, Locale, FallbackLocale, Composer, VueI18n } from 'vue-i18n'
 import type { NuxtApp } from '#app'
+import type { Ref } from '#imports'
 import type { Router } from '#vue-router'
 import type { DetectLocaleContext } from './internal'
 import type { HeadSafe } from '@unhead/vue'
@@ -90,12 +91,14 @@ export type CommonComposableOptions = {
   router: Router
   i18n: I18n
   runtimeConfig: RuntimeConfig
+  metaState: Ref<Record<Locale, any>>
 }
 export function initCommonComposableOptions(i18n?: I18n): CommonComposableOptions {
   return {
     i18n: i18n ?? useNuxtApp().$i18n,
     router: useRouter(),
-    runtimeConfig: useRuntimeConfig()
+    runtimeConfig: useRuntimeConfig(),
+    metaState: useState<Record<Locale, any>>('nuxt-i18n-meta', () => ({}))
   }
 }