You managed to blog this viewpoint before me, Ola, but you know I agree with almost everything. However, to pour a bit more oil on the fire, I'll take it a step further.
Having run the Ruby gauntlet and brought JRuby from not running anything to running Rails almost 100% perfectly (in just over a year, I might add), I will confidently say there's no way with current specs and tests that anyone could create an implementation of Ruby from scratch that will run Rails unless they can look at the existing implementations. I simply do not believe it's possible.
And I'll throw another couple curve balls too:
- I don't believe tests and specs will be where they need to be within the next 6-12 months unless there's a major effort put behind them. Even if that effort happens, I still don't think we'll ever have specs enough for someone to implement Ruby "in the dark" for at least a year, if it ever happens.
- IronPython did a great job getting pretty close to 100% compatible. But Jim Hugunin had implemented an almost 100% Python-compatible implementation in Jython before going to Microsoft; he didn't need to look at the Python source. I don't believe John Lam has the same level of experience with Ruby, so he's at a severe disadvantage (and to John: I really feel for you, man...this has got to be difficult).
- This is a good friend's belief, but he's won me over: we don't believe Microsoft would ever willingly allow IronRuby to get to the point of running Rails, since that would directly compete with their ASP.NET server, software, and tool offerings. What would be the benefit to them of a free runtime running a free language implementation that runs a free web framework? Probably zero. And as Martin Fowler and others have blogged about NUnit, Microsoft hasn't exactly been lovey-dovey with OSS projects that impact (or are perceived to impact) their bottom line.
- Given these facts and the current situation, I'd say it's a better bet for us as a community to get behind the Gardens Point Ruby.NET Compiler project, which is already much farther along than IronRuby...plus it's real open source (you can contribute) and they can look at Ruby's source (and have admitted to doing so for at least the parser). I was wary/skeptical of Ruby.NET last year, but they now seem like the current best hope for Ruby on the CLR. That link again is Gardens Point Ruby.NET Compiler. And to the QUT guys working on Ruby.NET, you need to do three things right now to save your project from historical obscurity: set up a public source repository, accept a few external contributors, and start blogging and emailing up a freaking storm.