file too small (length=0) file '/Users/xxx/Library/Developer/Xcode/DerivedData/xxxxA-clsrddebcymbreafkqrlswmmsbfw/Build/Intermediates.noindex/RxCocoa.build/Debug-iphoneos/RxCocoa.build/Objects-normal/arm64/Driver+Subscription.o'類似這個
file too small (length=0)的錯誤，clean一下再運行一下就可以了