Error: Could not build Objective-C module 'Firebase'

I am using Swift 4 and Xcode 9. All I have to do is selecting FirebaseCore Scheme.

On Xcode:

Product->Scheme->FirebaseCore.

If you don't have FirebaseCore go to Manage Schemes and select it. Then try again.

There is only one way to solve this issue.

1. Quit Xcode.
2. Delete project's temp files located at ~/Library/Developer/Xcode/DerivedData
3. Delete ProjectName.xcworkspace
4. Delete Podfile.lock file and Pods folder
5. Run pod install.
6. Open the newly created ProjectName.xcworkspace file and build.

Build (⌘ + B) worked for me.