test/ClangImporter/Inputs/custom-modules/PredefinedMacros.h - third_party/swift - Git at Google

 #if !defined(__swift__)
 # error "__swift__ not defined"
 #elif __swift__ < 30000
 # error "Why are you using such an old version of Swift?"
 #elif __swift__ >= 810000
 # error "Is Swift 81 out already? If so, please update this test."
 #else
 void swift3ReadyToGo();
 #endif
	#if !defined(__swift__)
	# error "__swift__ not defined"
	#elif __swift__ < 30000
	# error "Why are you using such an old version of Swift?"
	#elif __swift__ >= 810000
	# error "Is Swift 81 out already? If so, please update this test."
	#else
	void swift3ReadyToGo();
	#endif