fix(ament_cmake_python): respect DESTDIR during compilation

[AntoninRousset]

Make ament_cmake_python compilation respect DESTDIR.

[cottsay]

DESTDIR is typically not set during the compilation phase. Both Fedora and Debian packaging specify DESTDIR during make install but not the primary make invocation.

In what scenario do you feel this is needed?

[gentoo90]

@cottsay, It's pythons bytecode compilation and it IS called during install. I just stepped on this landmine on gentoo when it tried to compile the bytecode directly into /opt/ros/humble instead of /var/tmp/portage/ros-humble/<PACKAGE>/image/opt/ros/humble which was denied by the sandbox.

Please merge.

[cottsay]

How will this change behave on Windows, where CMAKE_INSTALL_PREFIX may be an absolute path which may include a drive letter?
I believe that VS-based builds currently ignore DESTDIR, but this would change that. If I'm not mistaken, DESTDIR is a Makefile-specific paradigm, not a CMake concept.

I'm not saying that we can't find a solution here, especially if the Makefiles aren't acting how they should, but I'm cautious about merging this as-is.

A question I have is how this is currently behaving in our deb and RPM builds on the buildfarm, which are currently using DESTDIR successfully.

[gentoo90]

A question I have is how this is currently behaving in our deb and RPM builds on the buildfarm, which are currently using DESTDIR successfully.

@cottsay, ros-humble-xacro_2.0.8-1jammy.20230919.194745_amd64.deb for example doesn't have *.pyc files in it, so compiling them is probably disabled on the buildfarm (e.g. ARG_SKIP_COMPILE is ON)

ament_cmake/ament_cmake_python/cmake/ament_python_install_module.cmake

Lines 61 to 71 in 53d31f3

	if(NOT ARG_SKIP_COMPILE)
	get_executable_path(python_interpreter Python3::Interpreter CONFIGURE)
	# compile Python files
	install(CODE
	"execute_process(
	COMMAND
	\"${python_interpreter}\" \"-m\" \"compileall\"
	\"${CMAKE_INSTALL_PREFIX}/${destination}/${module_file}\"
	)"
	)
	endif()