[SOLVED] CPack CPACK_RPM_PACKAGE_RELEASE cannot be set to 0

CPack CPACK_RPM_PACKAGE_RELEASE cannot be set to 0

I need to create a RPM of my software expecting the following output: <my_sw_name>-<version>-<release>.rpm.

The default for <release> shall be 0.

In my CMakeLists.txt I am using the following command:

cmake_minimum_required(VERSION 3.20)
...
set(SW_RELEASE 0)
set(CPACK_GENERATOR "RPM")
set(CPACK_RPM_PACKAGE_RELEASE ${SW_RELEASE})
set(CPACK_RPM_PACKAGE_RELEASE_DIST OFF)
set(CPACK_RPM_FILE_NAME "RPM-DEFAULT")
...

Nevertheless, the generated RPM filename is <my_sw_name>-<version>-1.rpm, and the Release: field in the RPM file is set to 1.

Is this a bug in CPack or did I miss something?

Solution

To any future users who aren't aware, It's conventional to start the release number for RPM packages at 1 and not at 0. And here's a link to the CPackRPM docs in case anyone needs it.

Reading through :/Modules/Internal/CPack/CPackRPM.cmake for CMake version 3.24.1, I think the culprit is the following code at line 965 inside the function cpack_rpm_generate_package:

  if(NOT CPACK_RPM_PACKAGE_RELEASE)
    set(CPACK_RPM_PACKAGE_RELEASE "1")
  endif()

The string 0 in CMake is falsy. Ex,

if(NOT 0)
  message("zero is falsy") # this will be reached and printed
endif()

Ie. your 0 causes the expression NOT CPACK_RPM_PACKAGE_RELEASE to evaluate to FALSE, and then your 0 gets clobbered to a 1.

If you want the value 0 to be supported, you could file an issue on the CMake gitlab repo requesting it. It would probably look like changing it to this:

  if(NOT DEFINED CPACK_RPM_PACKAGE_RELEASE)
    set(CPACK_RPM_PACKAGE_RELEASE "1")
  endif()

If this is truly the cause and you do file an issue to kitware, please either add a link to it as a comment under this answer, or to the end of the body of your question so future readers can find it.