Just a quick post, having finally figured out how to install dep_selector on mac os x. The issue is that having xcode installed which configures clang as the default compiler, some native gems break.

It took me some time, but at long least I can now build a native gem using gcc instead of clang on mac os x. And you’ll see it’s not very easy to have ruby change its compiler for gems native extensions compilation.

Installing gecode

brew install gecode is supposed to be fine, but it failed for me. The solution was to use llvm :

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$ brew install gecode --use-llvm

Install dep_selector

dep_selector uses the standard mkmf to create the makefile that will be used to build the native extension for the gem. mkmf in turn uses RbConfig, which is defined in rbconfig.rb deep in your ruby source and was generated when your ruby was built. The issue is that this rbconfig hard codes the value of the CC variable that will be used in the Makefile.

gem install dep_selector fails with compilation errors by clang.

• First solution : modify rbconfig.rb to use ENV['CC'] if defined. Yeah, that’d be ugly.
• Second solution : manually build the extension and let rubygems know that our gem is installed.

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$ cd $GEM_HOME/gems/dep_selector-0.0.8/ext/dep_gecode
$ # First let's confirm that this was built with the wrong compiler
$ grep clang Makefile
CC = clang

Now let’s edit the extconf.rb, adding the following line just before the last (create_makefile() thing).

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%w{CC CXX}.each do |c|
  RbConfig::MAKEFILE_CONFIG[c] = ENV[c] if ENV[c]
end

And let’s recreate the Makefile and build our extension.

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$ CC=gcc CXX=g++ ruby extconf.rb
$ grep CC Makefile # Should output gcc, great success !
$ make
$ make install # This will copy the library so to a proper ruby directory

We can check that the compilation worked, because there is now a dep_gecode.bundle file. Now we need to let the gem system know that our gem is added. The manual for gem install tells us that we’ll have to copy the gemspec. The following should do the trick :

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$ cd $GEM_HOME/gems/dep_selector-0.0.8
$ gem spec --local ../../cache/dep_selector-0.0.8.gem --ruby > ../../specifications/dep_selector-0.0.8.gemspec
$ gem list dep_selector
*** LOCAL GEMS ***

dep_selector (0.0.8)
$ irb
>> require 'dep_selector'
=> true
>> exit

That’s it, now we can move on and work on our chef install.