feat: merging of locale files with the same name for `@intlify/unplug…

…in-vue-i18n/messages` (#274)

* Fix merging of locale files with the same name

* Replace lodash.merge with a plain JS implementation

* Update README.md

packages/unplugin-vue-i18n/README.md

@@ -225,6 +225,8 @@ export default defineConfig({
   ],
 })
 ```
+unplugin-vue-i18n will automatically merge locale files into `@intlify/unplugin-vue-i18n/messages`. This allows locales to be split across multiple files, for example `src/locales/fruits/en.json` and `src/locales/vegetables/en.json`.
+
 ### Types
 
 If you want type definition of `@intlify/unplugin-vue-i18n/messages`, add `unplugin-vue-i18n/messages` to `compilerOptions.types` of your tsconfig:

packages/unplugin-vue-i18n/examples/vite/src/locales/en.yaml

@@ -1,3 +1 @@
 select: Do you want banana?
-fruits:
-  banana: 'no bananas | {n} banana | {n} bananas'

packages/unplugin-vue-i18n/examples/vite/src/locales/fruits/en.yaml

@@ -0,0 +1,2 @@
+fruits:
+  banana: 'no bananas | {n} banana | {n} bananas'

packages/unplugin-vue-i18n/examples/vite/src/locales/fruits/ja.json5

@@ -0,0 +1,5 @@
+{
+  fruits: {
+    banana: 'バナナがない | バナナ {n} 個'
+  }
+}

packages/unplugin-vue-i18n/examples/vite/src/locales/ja.json5

@@ -1,6 +1,3 @@
 {
-  select: "バナナが欲しい？",
-  fruits: {
-    banana: "バナナがない | バナナ {n} 個"
-  }
+  select: 'バナナが欲しい？'
 }

packages/unplugin-vue-i18n/examples/vite/src/main.ts

@@ -1,17 +1,12 @@
 import { createApp } from 'vue'
 import { createI18n } from 'vue-i18n'
 import App from './App.vue'
-import ja from './locales/ja.json5'
-import en from './locales/en.yaml'
-// import messages from '@intlify/vite-plugin-vue-i18n/messages'
+import messages from '@intlify/unplugin-vue-i18n/messages'
 
 const i18n = createI18n({
   legacy: false,
   locale: 'ja',
-  messages: {
-    ja,
-    en
-  }
+  messages
 })
 
 const app = createApp(App)

packages/unplugin-vue-i18n/src/index.ts

@@ -782,9 +782,29 @@ async function generateBundleResources(
     }
   }
 
-  return `export default {
-  ${codes.join(`,\n`)}
-}`
+  return `const isObject = (item) => item && typeof item === 'object' && !Array.isArray(item);
+
+const mergeDeep = (target, ...sources) => {
+  if (!sources.length) return target;
+  const source = sources.shift();
+
+  if (isObject(target) && isObject(source)) {
+    for (const key in source) {
+      if (isObject(source[key])) {
+        if (!target[key]) Object.assign(target, { [key]: {} });
+        mergeDeep(target[key], source[key]);
+      } else {
+        Object.assign(target, { [key]: source[key] });
+      }
+    }
+  }
+
+  return mergeDeep(target, ...sources);
+}
+
+export default mergeDeep({},
+  ${codes.map(code => `{${code}}`).join(',\n')}
+);`
 }
 
 async function getCode(