Added type safety

Author: Paritosh Maurya

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

@@ -1203,13 +1203,18 @@ export interface ComposerNumberFormatting<
    *
    * @returns Formatted value
    */
-  <Key extends string = string>(
+  <
+    Key extends string = string,
+    Return extends string | Intl.NumberFormatPart[] =
+      | string
+      | Intl.NumberFormatPart[]
+  >(
     value: number,
     keyOrOptions:
       | Key
       | ResourceKeys
       | NumberOptions<Key | ResourceKeys, Locales>
-  ): string | Intl.NumberFormatPart[]
+  ): Return
   /**
    * Number Formatting
    *
@@ -1224,14 +1229,19 @@ export interface ComposerNumberFormatting<
    *
    * @returns Formatted value
    */
-  <Key extends string = string>(
+  <
+    Key extends string = string,
+    Return extends string | Intl.NumberFormatPart[] =
+      | string
+      | Intl.NumberFormatPart[]
+  >(
     value: number,
     keyOrOptions:
       | Key
       | ResourceKeys
       | NumberOptions<Key | ResourceKeys, Locales>,
     locale: Locales
-  ): string | Intl.NumberFormatPart[]
+  ): Return
 }
 
 /**

packages/vue-i18n-core/test/composer.test-d.ts

@@ -357,8 +357,27 @@ test('strict composer with direct options', () => {
     string | Intl.NumberFormatPart[]
   >()
   expectTypeOf(
-    strictDirectComposer.n(1, { key: 'currency', locale: 'en' })
-  ).toEqualTypeOf<string | Intl.NumberFormatPart[]>()
+    strictDirectComposer.n<string, string>(1, 'currency', 'zh')
+  ).toEqualTypeOf<string>()
+  expectTypeOf(
+    strictDirectComposer.n<string, string>(1, { key: 'currency', locale: 'en' })
+  ).toEqualTypeOf<string>()
+  expectTypeOf(
+    strictDirectComposer.n<string, string>(1, { key: 'currency', locale: 'en' })
+  ).toEqualTypeOf<string>()
+  expectTypeOf(
+    strictDirectComposer.n<string, Intl.NumberFormatPart[]>(1, {
+      key: 'currency',
+      locale: 'en',
+      part: true
+    })
+  ).toEqualTypeOf<Intl.NumberFormatPart[]>()
+  expectTypeOf(strictDirectComposer.n(1, 'currency')).toEqualTypeOf<
+    string | Intl.NumberFormatPart[]
+  >()
+  expectTypeOf(
+    strictDirectComposer.n<string, string>(1, 'currency')
+  ).toEqualTypeOf<string>()
   expectTypeOf(strictDirectComposer.n(1, 'custom' as any)).toEqualTypeOf<
     string | Intl.NumberFormatPart[]
   >()

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

@@ -865,10 +865,23 @@ declare module 'vue' {
      *
      * @returns formatted value
      */
-    $n<OptionsType extends NumberOptions>(
+    $n<
+      Key extends string,
+      Return extends string | Intl.NumberFormatPart[] =
+        | string
+        | Intl.NumberFormatPart[],
+      DefinedNumberFormat extends
+        RemovedIndexResources<DefineDateTimeFormat> = RemovedIndexResources<DefineDateTimeFormat>,
+      Keys = IsEmptyObject<DefinedNumberFormat> extends false
+        ? PickupFormatPathKeys<{
+            [K in keyof DefinedNumberFormat]: DefinedNumberFormat[K]
+          }>
+        : never,
+      ResourceKeys extends Keys = IsNever<Keys> extends false ? Keys : never
+    >(
       value: number,
-      options: OptionsType
-    ): OptionsType['type'] extends true ? Intl.NumberFormatPart[] : string
+      options: NumberOptions<Key, ResourceKeys>
+    ): Return
     /**
      * Locale messages getter
      *