Add multi-sim support for phone auth

Author: morganchen12

PhoneAuth/FirebasePhoneAuthUI/CountryCode/FUICountryCodes.m

@@ -115,7 +115,36 @@ - (FUICountryCodeInfo *)countryCodeInfoAtIndex:(NSInteger)index {
 
 - (FUICountryCodeInfo *)defaultCountryCodeInfo {
  // Get the country code based on the information of user's telecommunication carrier provider.
- CTCarrier *carrier = [[[CTTelephonyNetworkInfo alloc] init] subscriberCellularProvider];
+ CTCarrier *carrier;
+ if (@available(iOS 12, *)) {
+ NSDictionary *carriers =
+ [[[CTTelephonyNetworkInfo alloc] init] serviceSubscriberCellularProviders];
+ // For multi-sim phones, use the current locale to make an educated guess for
+ // which carrier to use.
+ NSString *currentCountryCode = [NSLocale currentLocale].countryCode;
+ for (CTCarrier *provider in carriers.allValues) {
+ if ([provider isKindOfClass:[CTCarrier class]] &&
+ [provider.isoCountryCode isEqualToString:currentCountryCode]) {
+ carrier = provider;
+ break;
+ }
+ }
+
+ // If the carrier is still nil, grab a random carrier from the dictionary.
+ if (carrier == nil) {
+ for (CTCarrier *provider in carriers.allValues) {
+ if ([provider isKindOfClass:[CTCarrier class]]) {
+ carrier = provider;
+ break;
+ }
+ }
+ }
+ } else {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+ carrier = [[[CTTelephonyNetworkInfo alloc] init] subscriberCellularProvider];
+#pragma clang diagnostic pop
+ }
  NSString *countryCode = carrier.isoCountryCode ?: [[self class] countryCodeFromDeviceLocale];
  FUICountryCodeInfo *countryCodeInfo = [self countryCodeInfoForCode:countryCode];
  // If carrier is not available, get the hard coded default country code.