perf: skip the switch-locale-path html scan without a link

src/runtime/components/SwitchLocalePathLink.ts

@@ -5,6 +5,7 @@ import { hasProtocol } from 'ufo'
 import { nuxtLinkDefaults } from '#build/nuxt.config.mjs'
 import { useComposableContext } from '../composable-context'
 import { useNuxtI18nContext } from '../context'
+import { markSwitchLocalePathLink } from '../shared/switch-locale-path'
 
 import type { PropType } from 'vue'
 
@@ -68,6 +69,9 @@ export default defineComponent({
   },
   inheritAttrs: false,
   setup(props, { slots, attrs }) {
+    if (import.meta.server) {
+      markSwitchLocalePathLink(useNuxtApp().ssrContext)
+    }
     return () => [
       h(Comment, `${__SWITCH_LOCALE_PATH_LINK_IDENTIFIER__}-[${props.locale}]`),
       h(SlpComponent, { ...attrs, ...props }, slots.default),

src/runtime/plugins/switch-locale-path-ssr.ts

@@ -1,6 +1,7 @@
 import { defineNuxtPlugin, useNuxtApp } from '#imports'
 import { useSwitchLocalePath } from '#i18n'
 import { escapeHtmlAttr } from '../shared/utils'
+import { hasSwitchLocalePathLink } from '../shared/switch-locale-path'
 
 const identifier = __SWITCH_LOCALE_PATH_LINK_IDENTIFIER__
 const switchLocalePathLinkWrapperExpr = new RegExp(
@@ -17,7 +18,8 @@ export default defineNuxtPlugin({
     const nuxt = useNuxtApp(_nuxt._id)
     const switchLocalePath = useSwitchLocalePath(nuxt)
     nuxt.hook('app:rendered', (ctx) => {
-      if (ctx.renderResult?.html == null) { return }
+      // scanning the whole html costs time on every large page, so skip renders without a link
+      if (ctx.renderResult?.html == null || !hasSwitchLocalePathLink(ctx.ssrContext)) { return }
 
       ctx.renderResult.html = ctx.renderResult.html.replaceAll(
         switchLocalePathLinkWrapperExpr,

src/runtime/shared/switch-locale-path.ts

@@ -0,0 +1,12 @@
+import type { NuxtSSRContext } from '#app'
+
+// server renders that contain a `SwitchLocalePathLink`, so only those pay for the html rewrite
+const renders = new WeakSet<NuxtSSRContext>()
+
+export function markSwitchLocalePathLink(ssrContext: NuxtSSRContext | undefined) {
+  if (ssrContext) { renders.add(ssrContext) }
+}
+
+export function hasSwitchLocalePathLink(ssrContext: NuxtSSRContext | undefined) {
+  return !!ssrContext && renders.has(ssrContext)
+}