How to use Firebase in macOS

Issue #501

• Use Catalyst
• Add to CocoaPods

platform :ios, '13.0'

target 'MyApp' do
  use_frameworks!

  pod 'FirebaseCore'
  pod 'Firebase/Firestore'

end

Troubleshooting

Select a team for gRPC-C++-gRPCCertificates-Cpp

FIRAnalyticsConnector: building for Mac Catalyst, but linking in object file built for iOS Simulator

https://stackoverflow.com/questions/57666155/firanalyticsconnector-building-for-mac-catalyst-but-linking-in-object-file-bui

The problem was related to the difference between Firebase/Core and FirebaseCore. The first is a subspec of the Firebase pod that depends on FirebaseAnalytics. The second is only the FirebaseCore pod. Only the latter should be used for macOS.