I am developing a C/C++ package, built using CMake, and I want to package it for Debian. So I thought I’d use CPack to build a Debian package. I managed to do so, but my project should also contain configuration files, that should not be overwritten by package upgrades. IIUC, that’s what Debian conffiles are for, but I can’t figure out how to use CMake to insert them. Right now, it installs the files under /etc/myproject, but they get overwritten even if the info I found online seems to suggest that everything under /etc should be treated as a conffile. I also found that CPACK_DEBIAN_PACKAGE_CONTROL_EXTRA may help me, but I can’t figure out how should I use it. So, how can I instruct CMake/CPack to install conffiles?

My current relevant CMakeLists.txt is

###########
# Install #
###########
set(CMAKE_INSTALL_PREFIX "/opt/test/usr")
set(CPACK_PACKAGE_NAME test-package)
set(CPACK_PACKAGE_VENDOR "Test company")
set(CPACK_PACKAGE_CONTACT "[email protected]")
set(CPACK_PACKAGE_VERSION_MAJOR 0)
set(CPACK_PACKAGE_VERSION_MINOR 1)
set(CPACK_PACKAGE_VERSION_PATCH 2)
set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "Test package for CPack")
set(CPACK_GENERATOR DEB)
set(CPACK_DEBIAN_FILE_NAME DEB-DEFAULT)
set(CPACK_DEBIAN_PACKAGE_PRIORITY extra)

install(TARGETS ${PROJECT_NAME}
  DESTINATION bin)
install(TARGETS sub-proc-test    # two programs built from my MWE
  DESTINATION bin)
install(FILES                    # these SHOULD be conffiles
  ${CMAKE_SOURCE_DIR}/proc-test.env
  ${CMAKE_SOURCE_DIR}/sub-proc-test-1.env
  ${CMAKE_SOURCE_DIR}/sub-proc-test-2.env
  ${CMAKE_SOURCE_DIR}/proc-test-add.env
  DESTINATION /etc/test)         # installed here

include(CPack)