Infinite loop with a self-referential class

[catamorphism]

class kitten {
    let cat: option<cat>;
    new(cat: option<cat>) {
       self.cat = cat;
    }
}

type cat = @kitten;

fn main() {}

This program causes rustc to go into an infinite loop. I'd thought the infinite loop was in infer, but it seems to instead be in trans... so I'll keep looking.

[catamorphism]

It's pretty obvious why -- type_of goes into an infinite loop since it substitutes typedefs, and then it needs to know the LLVM type of kitten in order to compute the type of kitten (since a class's type is just a struct of its fields). But not sure what to do. This should be permitted.

[catamorphism]

The example compiles if I change type to enum in type cat, since then the typedef won't be substituted. I think it's bad that the original program infinite-loops, but I don't see an easy way out of it. To compute the type of the outer class kitten I need to know the types of each of its fields, and then to know the size of the cat field I need to know the type of kitten.

[pcwalton]

Fixed. This was blocking Servo.