enable_language(C CXX)

add_library(lib1 STATIC)
target_sources(lib1 PRIVATE lib1.c)
target_sources(lib1 PUBLIC FILE_SET a TYPE SOURCES FILES lib2.c)

set_source_files_properties(lib2.c PROPERTIES LANGUAGE C)
set_property(FILE_SET a TARGET lib1 PROPERTY LANGUAGE CXX)
set_property(FILE_SET a TARGET lib1 PROPERTY COMPILE_DEFINITIONS
  LIB1_A EXPECT_CXX "$<$<COMPILE_LANGUAGE:CXX>:EXPECTED_LANGUAGE>")
set_property(FILE_SET a TARGET lib1 PROPERTY INCLUDE_DIRECTORIES "${CMAKE_CURRENT_SOURCE_DIR}/subdir1")

set_property(FILE_SET a TARGET lib1 PROPERTY INTERFACE_COMPILE_DEFINITIONS
  INTERFACE_LIB1_A EXPECT_CXX "$<$<COMPILE_LANGUAGE:CXX>:EXPECTED_LANGUAGE>")
set_property(FILE_SET a TARGET lib1 PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${CMAKE_CURRENT_SOURCE_DIR}/subdir2")

add_executable(main main.c)
target_link_libraries(main PRIVATE lib1)
target_compile_definitions(main PRIVATE CONSUMER)

add_library(lib2 SHARED)
target_link_libraries(lib2 PRIVATE lib1)
target_compile_definitions(lib2 PRIVATE CONSUMER)