openSUSE is a gem for ruby development

In this post I would like to show what openSUSE has to offer to ruby enthusiasts.

The latest openSUSE version ships with ruby 1.8.7, rubygems 1.3.1 and rails 2.3.2. The latest two being not so recent, here is where the openSUSE project shines. Say hello to devel:languages:ruby and devel:languages:ruby:extensions build service projects.

The first is a project containing a more recent 1.8.7 ruby (p249 vs p72 in 11.2). However, as a build service project, it is built on top of multiple targets so you can add this repository not only to 11.2 but also to SLE and older openSUSE releases.

In this project you will also find a ruby19 package which is nothing else than ruby 1.9.1 p376 installable in parallel with 1.8.7.

The devel:languages:ruby:extensions contains ruby libraries and gems. For example you can find rails 2.3.5 there. Libraries are usually packaged as ruby-something and gems are packaged as rubygem-something. Gem packages have some nice attributes:

• They are visible by the software management stack (rpm ZYpp, and all the ZYpp integrated tools: PackageKit, YaST, etc)
• They are visible to the gem tool. The rpm is installed where the gem tools expects to find it
• They are the best choice if you want distribute a fully packaged application, or an appliance using SUSE Studio
• You can easily create them from a standard gem using the gem2rpm-opensuse script included in the rubygem-gem2rpm package

To add the gem repository to your 11.2 system, just do (as root):

zypper ar \
http://download.opensuse.org/repositories/devel:/languages:/ruby:/extensions/openSUSE_11.2 rubygems

Living on the edge

While the ruby environment provided by openSUSE is great, you may want to go one step further. What comes to my head:

• If you have both ruby and ruby19, you would need to have a different package for each ruby interpreter
• Sometimes you want to try a really experimental virtual machine, however openSUSE offers no package for it (eeer, and experimental VMs make packaging difficult, especially if the developers are MacOS users whose build script download prebuilt binaries of LLVM over the internet eeeek!)
• If you run or develop applications in the same machine, you may want to isolate the gem environment for each applications
• You may want quickly to test a program with different interpreters.
• You may not have root access! And sadly quacking like an administrator won’t give you superpowers.

Enter rvm, the ruby version manager

rvm is a nice tool that can quickly compile ruby interpreters from source and switch between them, all without root access (you can also set the current interpreter to the “system” one). Gems you install for one interpreter are isolated from the other interpreters, and you can create “gem sets”.

While rvm can be installed really easily:

bash < <( curl http://rvm.beginrescueend.com/releases/rvm-install-head )

for the HEAD version in github or

bash < <( curl http://rvm.beginrescueend.com/releases/rvm-install-latest )

You can also install it the “openSUSE way”, if you added the devel:languages:ruby:extensions repository:

zypper install rubygem-rvm

Once you have it installed, you will need to run rvm-install (as user) and edit your shell profile so that the environment is set correctly.

Then you can start using it. To see all the interpreters available in your system:

rvm list

To see all the ones known to rvm:

rvm list --all

Build 1.9 from source:

rvm install ruby-1.9.2-head

Build JRuby:

rvm install jruby

Use jruby:

rvm use jruby

Then you can “double check”:

ruby -v

jruby 1.4.0 (ruby 1.8.7 patchlevel 174) (2009-11-02 69fbfa3) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_20) [amd64-java]

Combine rvm with the powerful bundler

Of all the new ruby tools, the ones I find most useful is the bundler, which was created as a rails independent solution to make ruby applications specify the gems they need in their environment.

You can create a Gemfile in the top level directory of your application:

Something like.

source 'http://gemcutter.org'
gem "rails", "3.0.0.beta3"
gem "runt", :git => "http://github.com/tevio/runt.git"

As you can see, you can specify gems from git repositories, or use specific branches or versions. This is really nice for deployment, as you can get the working environment really easy.

bundle install

Would install the missing gems. It would reuse system gems, etc. If you are using rvm, it would install them in the interpreter specific gems.

The bundler has more advanced features, like the ability to take all the gems and “bundle” them directly “in” the application, but I leave that as an exercise to the reader.

Conclusions

So that finishes this post. I hope you could see how openSUSE looks like for a ruby developer.

I would like to first thanks Marcus Rückert (a.k.a darix) as he was the main brain behind the rubygem packages. Also big thanks to the YaST, Klaus, SUSE Studio and Build Service teams, whose development resulted in many package updates and contributions.

Reading a commit from DHH I found out a syntax I was not aware of.

Instead of doing:

[1,2,3,4,5,6,7,8,9,10].select { |x| x.even? }

You can do:

[1,2,3,4,5,6,7,8,9,10].select(&:even?)

When I asked in #rubyonrails irc channel about this syntax, I got enlightened: The first part is obvious: last argument starting with & is interpreted as a Proc and equivalent to passing a block, so it is not a &: operator but & and a symbol. How does the symbol work?

According to the people in the channel, it is rails magic. When I said that it works for me in irb I was told I must be running ruby 1.9, which I am not. After some discussion we realized this magic is in ruby 1.8.7 too.

The magic is of course, just Symbol#to_proc method

I was very happy that Rails Engines got merged in Rails 2.3. However I never liked that engines did not support overlaying static assets like they do with controllers, models and views. Even worse, the discussion was around “mirroring” the engine’s assets into the application public/ directory (like you can see in this railcast).

I imagined that doing something more transparent would be non-trivial. But I never asked myself why. When mentioning this limitation to Daniel when explaining how we use engines in our code, he asked the magical question: “Why?”.

I have been looking at Rails’s Rack support recently. I love Rack. And if you see how Rails builds its complex pieces over such simple components based on Rack, you realize how good Rack is for the Ruby community as a base component.

So, I tried the very first though: Create a Rake middleware called StaticOverlay that is initialized with various overlay directories. When the middleware is called it will look for the file in the overlays, and if it finds it in one, it will serve it (using Rack::File), if not, it just call the application (or next middleware in the chain).

Once I put the rack middleware together it worked out of the box, so I started a thread in rails core list to find out whether this would be a valid approach to hack a real patch and add support for this in Rails itself.

As you may know, are working on making YaST functionality accessible via the web. With this we mean not only browser. The current prototype has two parts: a generic web service (REST like API) and a web browser client.

Stefan Schubert announced last week a new snapshot for developers. You can find packages in the build service project. The packages are named yast2-webservice and yast2-webclient.

This is very early code. It is not fast, and the web client is not yet using all user interface possibilities that ajax gives, but there are we going .

If you are an experienced user, and you get it running, you may be interested in getting it running from source code by reading our development web page. Both the webservice and the webclient are rails applications. Developing modules is also easy! Just show up in irc (freenode) #yast.