rustc gets confused with classes that implement polymorphic ifaces

[eholk]

Here's a test case, and the compile error.

https://gist.github.com/3126225

[nikomatsakis]

It looks like the type parameter is not being instantiated to a fresh tvar. A mite confusing.

[catamorphism]

As I mentioned to @nikomatsakis earlier, I have a fix for this... but it breaks other test cases, so I'm still trying to figure out whether my fix was wrong or I exposed another bug.

[nikomatsakis]

@catamorphism sorry forgot to look at that with you today. Maybe you can gist the patch?

[nikomatsakis]

(or just push it to your local repo)