Firebase iOS - Undefined symbol: _GULResetLogger (arm64)

Question

I'm getting the following error when building my iOS app with XCode 12.0:

Undefined symbols for architecture arm64:
  "_GULResetLogger", referenced from:
      _FIRResetLogger in FirebaseCore(FIRLogger.o)
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

My Podfile looks like this:

platform :ios, '12.0'

target 'MyApp' do
    use_frameworks!
    pod 'Firebase/Firestore'
    pod 'Firebase/Auth'
    pod 'Firebase/RemoteConfig'
end

Previously my Podfile also contained pod 'Firebase/Core' but I've removed it as suggested here and re-installed my dependencies using the commands found in another answer:

pod deintegrate
pod cache clean --all
pod install

I've also run pod update to make sure I've got the latest dependencies, but I'm still getting the same error.

How can I get my app to build?

Answer 1

After hours of debugging I was finally able to work around this by doing the following:

1. Downgrade to Xcode 11.7 (explained here)
2. Clean install dependencies (explained here)
3. Clean Build Folder in under the Product menu in Xcode.

I still was not able to run the app on my device because iOS 14 is not supported by Xcode 11 (MobileDeviceErrorDomain error -402653150). Here is how I fixed this:

1. Install Device Support files for iOS 14.0 (explained here)
2. Unpair device from Xcode
3. Restart iPhone
4. Clean Build Folder