improve types declaration (#897)

* improve types declaration

* improve i18n types declaration

Co-authored-by: 双面胶 <[email protected]>

Author: littleboarx

packages/vue-i18n-core/src/i18n.ts

@@ -311,7 +311,11 @@ export function createI18n<
 >(
   options: Options,
   LegacyVueI18n?: any // eslint-disable-line @typescript-eslint/no-explicit-any
-): I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, Legacy>
+): typeof options['legacy'] extends true
+  ? I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, true>
+  : typeof options['legacy'] extends false
+  ? I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, false>
+  : I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, Legacy>
 
 /**
  * Vue I18n factory
@@ -410,7 +414,11 @@ export function createI18n<
 >(
   options: Options,
   LegacyVueI18n?: any // eslint-disable-line @typescript-eslint/no-explicit-any
-): I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, Legacy>
+): typeof options['legacy'] extends true
+  ? I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, true>
+  : typeof options['legacy'] extends false
+  ? I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, false>
+  : I18n<Messages, DateTimeFormats, NumberFormats, OptionLocale, Legacy>
 
 // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/explicit-module-boundary-types
 export function createI18n(options: any = {}, VueI18nLegacy?: any): any {

test-d/vue-i18n/i18n.test-d.ts

@@ -264,6 +264,26 @@ expectType<
     LocaleParams<'en' | 'ja'>
   >
 >(strictOptions)
+// check loose i18n composer
+const looseI18nComposer = createI18n({
+  ...looseOptions,
+  legacy: false
+}).global
+expectType<'en' | 'ja' | 'en-US' | 'ja-JP'>(looseI18nComposer.locale.value)
+expectType<{
+  en: {
+    foo: string
+    nest: {
+      bar: string
+    }
+  }
+  ja: {
+    bar: string
+    nest: {
+      bar: string
+    }
+  }
+}>(looseI18nComposer.messages.value)
 
 // check loose i18n
 const looseI18n = createI18n(looseOptions).global
@@ -376,7 +396,7 @@ looseI18n.mergeNumberFormat<{ echoes: { act: string } }>('ja-JP', {
 })
 
 // check strict i18n
-const strictI18n = createI18n<[ResourceSchema], 'en' | 'ja', false>(
+const strictI18n = createI18n<[ResourceSchema], 'en' | 'ja'>(
   strictOptions
 ).global
 expectType<'en' | 'ja'>(strictI18n.locale.value)