[CMake] Why CPack does not _ALWAYS_ use DESTDIR?

[Eric Noulard]

Hi All,

I did examine a problem with CPack RPM  generator which had
been reported by a user:
http://public.kitware.com/Bug/view.php?id=7000

The issue concerned file/target installed with absolute path name
which leads to the following error:
CMake Error at cmake_install.cmake:40 (FILE):
  file cannot create directory: /absolute/path. Maybe need administrative
  privileges.

/absolute/path being the absolute path used in a DESTINATION option
of some INSTALL command.

This error can be fixed if we either:

SET(CPACK_SET_DESTDIR "ON") in the CMakeList.txt
or
force the same option from within the concerned CPack Generator code.

Afterwards I've tested all CPack generator enabled on my Linux box
I did discover that ALL of them do encounter the same issue!!

My question is the following,

Why CPack does not _ALWAYS_ use DESTDIR?
Why should the user
SET(CPACK_SET_DESTDIR "ON") in the CMakeList.txt

I would really prefer to _ALWAYS_ set it ON i.e. get rid of it :=)

Does anybody knows why we sometimes DO NOT want to use DESTDIR
for CPack generator?
If there is no reason we may well enforce DESTDIR ON in the generic
part of all CPack generator.

-- 
Erk