Tests/RunCMake/target_sources/FileSetNoExistPrivate.cmake - third_party/github.com/Kitware/CMake - Git at Google

 enable_language(C)

 add_library(lib1 STATIC empty.c)
 set_property(TARGET lib1 PROPERTY HEADER_SETS "a")

 # Error happens at configure-time, so this doesn't help.
 target_sources(lib1 PRIVATE FILE_SET a TYPE HEADERS)
	enable_language(C)

	add_library(lib1 STATIC empty.c)
	set_property(TARGET lib1 PROPERTY HEADER_SETS "a")

	# Error happens at configure-time, so this doesn't help.
	target_sources(lib1 PRIVATE FILE_SET a TYPE HEADERS)