FindRuby.cmake

[Alexander Neundorf]

Hi Michael,

On Monday 07 March 2011, Michael Jansen wrote:
> Ruby has three different installation areas for libraries. Each
> installation area has two different subdirectories (sort of). One is for
> architecure independent files. One is for architecture dependent files.
>
> 1. Installation Area: Ruby Library Directory
>
>         rubylibdir  /usr/lib64/ruby/1.8
>            archdir  /usr/lib64/ruby/1.8/x86_64-linux
>
> This area is reserved for the ruby standard library (http://www.ruby-
> doc.org/stdlib/). No other software is supposed to be installed into this
> directory. It makes no sense for the cmake file to determine and provide
> the path and location of this area. You don't want to install stuff there
> and you don't need to get stuff from there. (The libruby.so is somewhere
> else)
>
> 2. Installation Area: Vendor
>
>            vendordir  /usr/lib64/ruby/vendor_ruby
>         vendorlibdir  /usr/lib64/ruby/vendor_ruby/1.8
>        vendorarchdir  /usr/lib64/ruby/vendor_ruby/1.8/x86_64-linux
>
> This area is intended to be used by distributions. They install the
> libraries provided by distribution packages into that area. You are
> supposed to install into that area if you build distro packages. It
> therefore makes sense to determine and provide this area from
> FindRuby.cmake
>
> 3. Installation Area: Site
>
> This area is intended to be used for self compiled and installed ruby
> packages. This is the most likely installation area for a ruby extension.
>
> 4. Installation Area: Custom
>
> In Addition to those 3 areas it is possible to install ruby extensions into
> custom directories and add their path to ruby $LOAD_PATH global array. Each
> directory has to be added explicitly. There is no automatic archdir
> handling.
>
>     a) $LOAD_PATH << "<custom_ruby_libdir>" << "<custom_ruby_archdir>"
>     b) ruby -I<path1> -I<path2>
>     c) Environment Variable RUBY_LIB and/or DLN_LIBRARY_PATH
>
> The current FindRuby.cmake determines the location of the areas 1, 2 ( if
> it exists) and 3. It does not advise or support chosing any installation

Do you mean the FindRuby.cmake shipped with cmake, the FindRUBY.cmake in 
kdelibs, or another one ?

> prefix to use. The ruby bindings use the simplest way and just install into
> the site area unless someone specifies a different path. Which is annoying
> if CMAKE_INSTALL_PREFIX is not the same as the ruby install prefix. But it
> is annoying too if you have to manually construct the correct path to one
> of the installation areas just to install your stuff into the ruby prefix.
> The ruby version and rubyarch are not obvious from the outside for both use
> cases.
>
> The features i would like to implement are:
>
> Provide two variables named
>     RUBY_INSTALL_LIBDIR
>     RUBY_INSTALL_ARCHDIR
>
> First rule wins:
>
> 1. If option RUBY_(USE_?)INSTALL_AREA is set to "site"

I guess this is intended to be a cache variable, so it can be set by the 
person who builds the package ?

>     RUBY_INSTALL_LIBDIR  = ${RUBY_SITELIB_DIR}
>     RUBY_INSTALL_ARCHDIR = ${RUBY_SITEARCH_DIR}
>
> 2. If option RUBY_INSTALL_AREA is set to "vendor" and a vendor install area
> exists (if not error)
>     RUBY_INSTALL_LIBDIR  = ${RUBY_VENDORLIB_DIR}
>     RUBY_INSTALL_ARCHDIR = ${RUBY_VENDORARCH_DIR}
>
> 3. If option RUBY_INSTALL_AREA is set to something else
>     error

I'd suggest a 3rd option "auto", which has the same effect as if 
RUBY_INSTALL_AREA is not set. Then we all three valid options can be listed 
using
set_property(CACHE RUBY_INSTALL_AREA PROPERTY STRINGS vendor;site;auto)
once we require cmake >= 2.8.0.
This has the effect that when using cmake-gui, the possible options are 
presented in a combo box.

> 4. if CMAKE_INSTALL_PREFIX is the same as the ruby install prefix
>     RUBY_INSTALL_LIBDIR  = ${RUBY_SITELIB_DIR}
>     RUBY_INSTALL_ARCHDIR = ${RUBY_SITEARCH_DIR}
>
> 5. If CMAKE_INSTALL_PREFIX is not the same as the ruby install prefix
> install set
>     RUBY_INSTALL_LIBDIR  =
> ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX}/ruby/${RUBY_VERSION}
>     RUBY_INSTALL_ARCHDIR =
> ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX}/ruby/${RUBY_VERSION}/${RUBY_ARCH}
>     and print out a hint how to activate this area for ruby (see above)
>
> This solution would make it possible to have all ruby extensions support
> this advanced functionality at once without each and everyone of them
> trying to support (or neglecting to) it by itself.

Sounds reasonable.

> The question is if such a functionality is appropriate for a cmake file.

If documented properly, I think it makes sense.

> If we finish this i would like to add the same functionality for python
> (PYTHON_(USE_?)INSTALL_AREA).

Marcus, you are caring about the python support in cmake, right ?
What's your opinion on this ?

Alex