[CMake] Proper behaviour and use of CMAKE_INSTALL_* variables

[Mojca Miklavec]

Dear list members,

I often like or need to install two versions of the same software.
Ideally the software should put its files by default to
    $prefix/include/$NAME/*.h
    $prefix/lib/$NAME/*.dylib
    ...
($prefix => $CMAKE_INSTALL_PREFIX)

and in order to be able to install multiple versions side-by-side I
would like to be able to specify something like
    -DCMAKE_INSTALL_INCLUDEDIR=include/$NAME/$VERSION
    -DCMAKE_INSTALL_LIBDIR=lib/$NAME/$VERSION
to end up with
    $prefix/include/$NAME/$VERSION/*.h
    $prefix/lib/$NAME/$VERSION/*.dylib
instead of default paths.

The problem is that in this case either of the two options must be true:

a) Software sets CMAKE_INSTALL_INCLUDEDIR to "include/$NAME" rather
than to "include" by default which "violates" the convention from
http://www.cmake.org/cmake/help/v2.8.12/cmake.html#module:GNUInstallDirs,
but leads to the desired behaviour.

b) Software sets CMAKE_INSTALL_INCLUDEDIR to "include" by default and
automatically adds "$NAME" to an internal variable when installing the
files. The drawback of this approach is that
    -DCMAKE_INSTALL_INCLUDEDIR=include/$NAME/$VERSION
results in files being installed to
    $prefix/include/$NAME/$VERSION/$NAME/*.h
and there is absolutely no way to change that.


What approach would you suggest to achieve the desired behaviour
without violating the conventions?

Thank you very much,
    Mojca