[in_app_purchase_platform_interface] Adds countryCode API (#6548)

Original pr #6540

Related to flutter/flutter#141627

Author: reidbaker

packages/in_app_purchase/in_app_purchase_platform_interface/CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## 1.4.0
 
+* Adds `getCountryCode` API.
 * Updates minimum supported SDK version to Flutter 3.13/Dart 3.1.
 
 ## 1.3.7
@@ -39,7 +40,7 @@
 
 ## 1.3.0
 
-* Added new `PurchaseStatus` named `canceled` to distinguish between an error and user cancellation. 
+* Added new `PurchaseStatus` named `canceled` to distinguish between an error and user cancellation.
 
 ## 1.2.0
 

packages/in_app_purchase/in_app_purchase_platform_interface/lib/src/in_app_purchase_platform.dart

@@ -194,4 +194,21 @@ abstract class InAppPurchasePlatform extends PlatformInterface {
   ///    [PurchaseDetails.verificationData].
   Future<void> restorePurchases({String? applicationUserName}) =>
       throw UnimplementedError('restorePurchases() has not been implemented.');
+
+  /// Returns the user's country.
+  ///
+  /// Android:
+  /// Returns Play billing country code based on ISO-3166-1 alpha2 format.
+  ///
+  /// See: https://developer.android.com/reference/com/android/billingclient/api/BillingConfig
+  /// See: https://unicode.org/cldr/charts/latest/supplemental/territory_containment_un_m_49.html
+  ///
+  /// iOS:
+  /// Returns the country code from SKStoreFrontWrapper.
+  ///
+  /// See: https://developer.apple.com/documentation/storekit/skstorefront?language=objc
+  ///
+  ///
+  Future<String> countryCode() =>
+      throw UnimplementedError('countryCode() has not been implemented.');
 }

packages/in_app_purchase/in_app_purchase_platform_interface/pubspec.yaml

@@ -4,7 +4,7 @@ repository: https://github.com/flutter/packages/tree/main/packages/in_app_purcha
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+in_app_purchase%22
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 1.3.7
+version: 1.4.0
 
 environment:
   sdk: ^3.1.0

packages/in_app_purchase/in_app_purchase_platform_interface/test/in_app_purchase_platform_test.dart

@@ -119,6 +119,18 @@ void main() {
         throwsUnimplementedError,
       );
     });
+
+    test(
+        'Default implementation of countryCode should throw unimplemented error',
+        () {
+      final ExtendsInAppPurchasePlatform inAppPurchasePlatform =
+          ExtendsInAppPurchasePlatform();
+
+      expect(
+        () => inAppPurchasePlatform.countryCode(),
+        throwsUnimplementedError,
+      );
+    });
   });
 
   group('$InAppPurchasePlatformAddition', () {