Xcode 12 using Firebase pods. Lexical or Preprocessor issue. "pb.h' file not found with <angled> include; use "quotes" instead"?

Update to CocoaPods 1.10, run pod deintegrate and pod install.

To work around in earlier CocoaPods versions, disable the CLANG_WARN_QUOTED_INCLUDE_IN_FRAMEWORK_HEADER option in the generate Pods project Build Settings:

More details in https://github.com/firebase/firebase-ios-sdk/issues/5987 and https://github.com/CocoaPods/CocoaPods/issues/9902.

I fixed it by using the the pre-release of cocoapods

sudo gem install cocoapods --pre

and then doing an update

pod install --repo-update

My team didn't want to use cocoapods 1.10 before it's released, and didn't want to re-edit the Pods project's build settings every time a pod install regenerates it. This Podfile post_install step did the trick, credit to Léo-Paul JULIE:

post_install do |installer|
  installer.pods_project.build_configurations.each do |config|
      config.build_settings['CLANG_WARN_QUOTED_INCLUDE_IN_FRAMEWORK_HEADER'] = 'NO'
    end
end

Edit: As snakeoil points out below, you can also silence annoying warnings about irrelevant iOS versions which you are not supporting. But that setting should probably be edited for each target's configuration's build settings, so in a nested loop. All together, I'm going with something like this for now:

post_install do |installer|
  installer.pods_project.build_configurations.each do |config|
    # Can be removed when moving to cocoapods 1.10
    config.build_settings['CLANG_WARN_QUOTED_INCLUDE_IN_FRAMEWORK_HEADER'] = 'NO'
  end
  installer.pods_project.targets.each do |target|
    target.build_configurations.each do |config|
      # Inherit the deployment target defined in this Podfile instead, e.g. platform :ios, '11.0' at the top of this file
      config.build_settings.delete 'IPHONEOS_DEPLOYMENT_TARGET'
    end
  end
end