# lib/foo/CMakeLists.txt
add_library(foo INTERFACE)
target_sources(foo INTERFACE foo.hpp)
target_include_directories(foo INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})

# bar/CMakeLists.txt
add_executable(bar main.cpp)  # Fails at this line with an error saying "missing foo.hpp"
target_link_libraries(bar foo)