feat: support layer locales and pages (#1925)

* feat: support layer locales and pages

* fix: locales not merged when lazy is false

* test: add basic layers test

* fix: layer locales not being bundled correctly

* docs: add layers page

* feat: change playground to illustrate layer override behavior

* test: add additional layer tests

* refactor: restructure layers implementation

* fix: update lockfile

.vscode/settings.json

@@ -10,4 +10,4 @@
     "source.fixAll.eslint": true
   },
   "typescript.tsdk": "node_modules/typescript/lib"
-}
+}

docs/content/2.guide/15.layers.md

@@ -0,0 +1,87 @@
+# Layers
+
+Nuxt i18n module supports layers and will automatically combine i18n configuration of all extended layers. [Read more about layers here](https://nuxt.com/docs/getting-started/layers)
+
+---
+
+### Merging strategy
+As described in the [Nuxt layer authoring guide](https://nuxt.com/docs/guide/going-further/layers#multi-layer-support-for-nuxt-modules) 
+> * Earlier items in the `_layers` array have higher priority and override later ones
+> * The user's project is the first item in the `_layers` array
+
+Mixing locale configuration such as lazy loading objects and strings may not work as expected, Nuxt i18n will attempt to merge layers as best it can. Consistency of i18n configuration between layers will be most effective.
+
+
+### Pages & Routing
+
+Pages in the `pages` directory from extended layers will automatically be merged and have i18n support as if they were part of your project. 
+
+Page routes defined in `i18n.pages` in each layer configuration will be merged as well.
+
+### Locales
+::alert{type="warning"}
+A project extending layers containing lazy-loaded translations is still required to have `lazy` and `langDir` options configured.
+::
+
+Extending your project with a layer that contains locales can be done as follows:
+
+::code-group
+  ::code-block{label="Project config" active}
+  ```ts {} [nuxt.config.ts]
+  export default defineNuxtConfig({
+    extends: ['my-layer'],
+    modules: ['@nuxtjs/i18n'],
+    i18n: {
+      lazy: true,
+      langDir: './lang',
+      locales: [{ code: 'en', file: 'en.json' }],
+    },
+  })
+  ```
+  ::
+  ::code-block{label="Layer config"}
+  ```ts
+  export default defineNuxtConfig({
+    modules: ['@nuxtjs/i18n'],
+    i18n: {
+      lazy: true,
+      langDir: './lang',
+      locales: [
+        { code: 'en', file: 'en.json' },
+        { code: 'nl', file: 'nl.json' },
+      ],
+    },
+  })
+  ```
+  ::
+::
+
+This example would result in the project supporting two locales (`en`, `nl`) and would add the additional messages added for the `en` locale.
+
+::code-group
+  ::code-block{label="project/lang/en.json" active}
+  ```ts {} [project/lang/en.json]
+  {
+    "title": "foo"
+  }
+  ```
+  ::
+  ::code-block{label="project/my-layer/lang/en.json"}
+  ```ts {} [project/my-layer/lang/en.json]
+  {
+    "title": "layer title",
+    "description": "bar"
+  }
+  ```
+  ::
+  ::code-block{label="result en.json"}
+  ```ts {} [result]
+  {
+    // earlier layers take priority
+    "title": "foo",
+    "description": "bar"
+  }
+  ```
+  ::
+::
+

playground/layers/i18n-layer/locales/en.json

@@ -0,0 +1,3 @@
+{
+	"layerText": "This is a merged locale key"
+}

playground/layers/i18n-layer/locales/fr.json

@@ -0,0 +1,3 @@
+{
+	"layerText": "This is a merged locale key in French"
+}

playground/layers/i18n-layer/locales/nl.json

@@ -0,0 +1,3 @@
+{
+	"layerText": "This is a merged locale key in Dutch"
+}

playground/layers/i18n-layer/nuxt.config.ts

@@ -0,0 +1,62 @@
+// import type { NuxtApp } from 'nuxt/dist/app/index'
+
+// https://nuxt.com/docs/guide/directory-structure/nuxt.config
+export default defineNuxtConfig({
+  modules: ['@nuxtjs/i18n'],
+  i18n: {
+    langDir: 'locales',
+    lazy: true,
+    baseUrl: 'http://localhost:3000',
+    customRoutes: 'config',
+    pages: {
+      history: {
+        en: '/history',
+        fr: '/history-fr',
+        nl: '/geschiedenis'
+      }
+    },
+    locales: [
+      {
+        code: 'en',
+        iso: 'en-US',
+        file: 'en.json',
+        // domain: 'localhost',
+        name: 'English'
+      },
+      {
+        code: 'fr',
+        iso: 'fr-FR',
+        file: 'fr.json',
+        // domain: 'localhost',
+        name: 'Francais'
+      },
+      {
+        code: 'nl',
+        iso: 'nl-NL',
+        file: 'nl.json',
+        // domain: 'localhost',
+        name: 'Nederlands'
+      }
+      //   {
+      //     code: 'en-GB',
+      //     iso: 'en-GB',
+      //     files: ['en.json', 'en-GB.json'],
+      //     name: 'English (UK)'
+      //   },
+      //   {
+      //     code: 'ja',
+      //     iso: 'ja-JP',
+      //     file: 'ja.json',
+      //     domain: 'mydomain.com',
+      //     name: 'Japanses'
+      //   },
+      //   {
+      //     code: 'fr',
+      //     iso: 'fr-FR',
+      //     file: 'fr.json',
+      //     domain: 'mydomain.fr',
+      //     name: 'Français'
+      //   }
+    ]
+  }
+})

playground/layers/i18n-layer/pages/about.vue

@@ -0,0 +1,9 @@
+<script setup lang="ts">
+definePageMeta({
+  title: 'Empty about page!'
+})
+</script>
+
+<template>
+  <div>This about page is empty!</div>
+</template>

playground/layers/i18n-layer/pages/history.vue

@@ -0,0 +1,3 @@
+<template>
+  <div></div>
+</template>

playground/nuxt.config.ts

@@ -3,8 +3,8 @@ import type { NuxtApp } from 'nuxt/dist/app/index'
 
 // https://nuxt.com/docs/guide/directory-structure/nuxt.config
 export default defineNuxtConfig({
+  extends: ['layers/i18n-layer'],
   modules: [Module1, '@nuxtjs/i18n', '@nuxt/devtools'],
-
   vite: {
     build: {
       minify: false
@@ -71,6 +71,9 @@ export default defineNuxtConfig({
     dynamicRouteParams: true,
     // customRoutes: 'config',
     pages: {
+      history: {
+        ja: '/history-ja'
+      },
       about: {
         ja: '/about-ja'
       }

playground/pages/index.vue

@@ -18,6 +18,8 @@ console.log('route base name', getRouteBaseName())
 console.log('useBrowserLocale', useBrowserLocale())
 console.log('localeProperties', localeProperties)
 console.log('foo', t('foo'))
+console.log('message if local layer merged:', t('layerText'))
+console.log('message if github layer merged:', t('layer-test-key'))
 
 function getLocaleName(code: string) {
   const locale = (locales.value as LocaleObject[]).find(i => i.code === code)
@@ -54,7 +56,8 @@ definePageMeta({
     <nav>
       <NuxtLink :to="localePath('/')">Home</NuxtLink> | <NuxtLink :to="localePath({ name: 'about' })">About</NuxtLink> |
       <NuxtLink :to="localePath({ name: 'blog' })">Blog</NuxtLink> |
-      <NuxtLink :to="localePath({ name: 'category-id', params: { id: 'foo' } })">Category</NuxtLink>
+      <NuxtLink :to="localePath({ name: 'category-id', params: { id: 'foo' } })">Category</NuxtLink> |
+      <NuxtLink :to="localePath({ name: 'history' })">History</NuxtLink>
     </nav>
     <h2>Current Language: {{ getLocaleName(locale) }}</h2>
     <h2>Current Strategy: {{ strategy }}</h2>