perf(i18n): load the i18n runtime only when the app uses i18n

src/module.ts

@@ -15,6 +15,7 @@ import {
   createResolver,
   defineNuxtModule,
   extendRouteRules,
+  hasNuxtModule,
   importModule,
   resolveModule,
 } from '@nuxt/kit'
@@ -307,6 +308,14 @@ export default defineNuxtModule<ModuleOptions>({
       nuxt.hook('close', unregister)
     }
 
+    // Route rule matching strips locale prefixes. Apps without i18n get an identity function and no i18n runtime code.
+    addServerTemplate({
+      filename: '#nuxt-robots/i18n.mjs',
+      getContents: () => hasNuxtModule('@nuxtjs/i18n') || nuxt.options.runtimeConfig.public.i18n
+        ? `export { withoutLocalePrefix } from ${JSON.stringify(resolve('./runtime/server/util/withoutLocalePrefix'))}`
+        : 'export const withoutLocalePrefix = path => path',
+    })
+
     // Allow `definePageMeta({ robots: false })` to set per-page robots rules
     nuxt.options.experimental.extraPageMetaExtractionKeys = nuxt.options.experimental.extraPageMetaExtractionKeys || []
     if (!nuxt.options.experimental.extraPageMetaExtractionKeys.includes('robots'))

src/runtime/server/composables/getPathRobotConfig.ts

@@ -1,41 +1,16 @@
 import type { RequestEvent } from 'nuxt/server'
-import type { RuntimeI18nConfig } from 'nuxtseo-shared/i18n-runtime'
 import type { RobotsContext } from '../../types'
 import { matchPathToRule, normaliseRobotsRouteRule } from '@nuxtjs/robots/util'
 import { getRequestHeader, matchRouteRules, useRuntimeConfig } from 'nuxt/server'
-import { resolveLocaleFromRoute } from 'nuxtseo-shared/i18n-runtime'
 import { parseURL, withoutBase, withoutTrailingSlash } from 'ufo'
 // @ts-expect-error Virtual server template registered by the module.
+import { withoutLocalePrefix } from '#nuxt-robots/i18n.mjs'
+// @ts-expect-error Virtual server template registered by the module.
 import { pageMetaMatchers } from '#nuxt-robots/page-meta.mjs'
 import { useNitroApp } from '#nuxtseo/nitro'
 import { getSiteRobotConfig } from './getSiteRobotConfig'
 import { useRuntimeConfigNuxtRobots } from './useRuntimeConfigNuxtRobots'
 
-const i18nStrategies = new Set<RuntimeI18nConfig['strategy']>(['no_prefix', 'prefix_except_default', 'prefix', 'prefix_and_default'])
-
-function parseRuntimeI18nConfig(input: unknown): RuntimeI18nConfig | null {
-  if (!input || typeof input !== 'object')
-    return null
-  const config = input as Record<string, unknown>
-  if (!Array.isArray(config.locales))
-    return null
-  const locales = config.locales.flatMap((locale) => {
-    const code = typeof locale === 'string'
-      ? locale
-      : locale && typeof locale === 'object' && typeof (locale as Record<string, unknown>).code === 'string'
-        ? (locale as Record<string, string>).code
-        : null
-    return code ? [{ code, hreflang: code }] : []
-  })
-  if (!locales.length)
-    return null
-  const defaultLocale = typeof config.defaultLocale === 'string' ? config.defaultLocale : locales[0]!.code
-  const strategy = typeof config.strategy === 'string' && i18nStrategies.has(config.strategy as RuntimeI18nConfig['strategy'])
-    ? config.strategy as RuntimeI18nConfig['strategy']
-    : 'prefix'
-  return { defaultLocale, locales, strategy }
-}
-
 export function getPathRobotConfig(e: RequestEvent, options?: { userAgent?: string, skipSiteIndexable?: boolean, path?: string }): RobotsContext {
   const runtimeConfig = useRuntimeConfig()
   // has already been resolved
@@ -116,11 +91,10 @@ export function getPathRobotConfig(e: RequestEvent, options?: { userAgent?: stri
   // if we're using i18n we need to strip leading prefixes so the rule will match
   // note this is for < v10 i18n behavior as it now handles route rules itself
   // TODO we may consider checking the version explicitly rather than the presence of the rules
-  const i18nConfig = parseRuntimeI18nConfig((runtimeConfig.public as Record<string, unknown>)?.i18n)
-  if (i18nConfig && typeof robotRouteRules.robots === 'undefined') {
-    const resolvedRoute = resolveLocaleFromRoute(routeRulesPath, i18nConfig)
-    if (resolvedRoute.basePath !== routeRulesPath) {
-      routeRulesPath = resolvedRoute.basePath
+  if (typeof robotRouteRules.robots === 'undefined') {
+    const basePath: string = withoutLocalePrefix(routeRulesPath, runtimeConfig.public as Record<string, unknown>)
+    if (basePath !== routeRulesPath) {
+      routeRulesPath = basePath
       robotRouteRules = matchRules(routeRulesPath)
     }
   }

src/runtime/server/util/withoutLocalePrefix.ts

@@ -0,0 +1,38 @@
+import type { RuntimeI18nConfig } from 'nuxtseo-shared/i18n-runtime'
+import { resolveLocaleFromRoute } from 'nuxtseo-shared/i18n-runtime'
+
+// The module loads this file only when the app uses i18n. Other apps get an identity function.
+
+const i18nStrategies = new Set<RuntimeI18nConfig['strategy']>(['no_prefix', 'prefix_except_default', 'prefix', 'prefix_and_default'])
+
+function parseRuntimeI18nConfig(input: unknown): RuntimeI18nConfig | null {
+  if (!input || typeof input !== 'object')
+    return null
+  const config = input as Record<string, unknown>
+  if (!Array.isArray(config.locales))
+    return null
+  const locales = config.locales.flatMap((locale) => {
+    const code = typeof locale === 'string'
+      ? locale
+      : locale && typeof locale === 'object' && typeof (locale as Record<string, unknown>).code === 'string'
+        ? (locale as Record<string, string>).code
+        : null
+    return code ? [{ code, hreflang: code }] : []
+  })
+  if (!locales.length)
+    return null
+  const defaultLocale = typeof config.defaultLocale === 'string' ? config.defaultLocale : locales[0]!.code
+  const strategy = typeof config.strategy === 'string' && i18nStrategies.has(config.strategy as RuntimeI18nConfig['strategy'])
+    ? config.strategy as RuntimeI18nConfig['strategy']
+    : 'prefix'
+  return { defaultLocale, locales, strategy }
+}
+
+/**
+ * Remove the locale prefix from a path, so a route rule for `/secret` matches `/fr/secret`.
+ * Returns the path unchanged when the public runtime config has no i18n locales.
+ */
+export function withoutLocalePrefix(path: string, publicRuntimeConfig: Record<string, unknown>): string {
+  const i18nConfig = parseRuntimeI18nConfig(publicRuntimeConfig.i18n)
+  return i18nConfig ? resolveLocaleFromRoute(path, i18nConfig).basePath : path
+}

test/e2e/i18n-route-rules-prefix.test.ts

@@ -0,0 +1,28 @@
+import { createResolver } from '@nuxt/kit'
+import { $fetch, setup } from '@nuxt/test-utils'
+import { describe, expect, it } from 'vitest'
+
+const { resolve } = createResolver(import.meta.url)
+
+process.env.NODE_ENV = 'production'
+
+await setup({
+  rootDir: resolve('../fixtures/i18n'),
+  build: true,
+  server: true,
+  nuxtConfig: {
+    routeRules: {
+      '/admin/**': { robots: false },
+    },
+  },
+})
+
+function robotsMeta(html: string) {
+  return html.match(/<meta name="robots" content="([^"]+)">/)?.[1]
+}
+
+describe('i18n route rules', () => {
+  it('applies an unprefixed route rule to a locale prefixed path', async () => {
+    expect(robotsMeta(await $fetch<string>('/fr/admin/login?mockProductionEnv=true'))).toBe('noindex, nofollow')
+  })
+})