ruby-on-rails – `build_extensions’：错误：无法构建gem原生

Could not find json-1.5.4 in any of the sources
Run `bundle install` to install missing gems.

如果我然后跑

bundle install json

我收到以下错误

Installing json (1.5.4) with native extensions /Library/Ruby/Site/1.8/rubygems/installer.rb:556:in `build_extensions': ERROR: Failed to build gem native extension. (Gem::Installer::ExtensionBuildError)

        /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb 
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/ruby.h


Gem files will remain installed in /Applications/RubyApps/skatemyspot/json/ruby/1.8/gems/json-1.5.4 for inspection.
Results logged to /Applications/RubyApps/skatemyspot/json/ruby/1.8/gems/json-1.5.4/ext/json/ext/parser/gem_make.out
    from /Library/Ruby/Site/1.8/rubygems/installer.rb:509:in `each'
    from /Library/Ruby/Site/1.8/rubygems/installer.rb:509:in `build_extensions'
    from /Library/Ruby/Site/1.8/rubygems/installer.rb:180:in `install'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/source.rb:101:in `install'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/rubygems_integration.rb:78:in `preserve_paths'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/source.rb:91:in `install'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/installer.rb:58:in `run'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/rubygems_integration.rb:93:in `with_build_args'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/installer.rb:57:in `run'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/installer.rb:49:in `run'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/installer.rb:8:in `install'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/cli.rb:220:in `install'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/vendor/thor/task.rb:22:in `send'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/vendor/thor/task.rb:22:in `run'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/vendor/thor/invocation.rb:118:in `invoke_task'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/vendor/thor.rb:263:in `dispatch'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/lib/bundler/vendor/thor/base.rb:386:in `start'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.0.18/bin/bundle:13
    from /usr/bin/bundle:19:in `load'
    from /usr/bin/bundle:19

我在nokogiri – ERROR: Failed to build gem native extension看到了答案,但我已经运行了Xcode 4.3.2.

有任何想法吗？谢谢