ICE with unbound node ID and cross crate traits

[erickt]

This may be a dup of #3108. Here's an distilled example of the error: https://gist.github.com/3458927. It fails with:

error: internal compiler error: node_id_to_type: unbound node ID unknown node (id=107518)

I tried importing the trait into the local scope, but that didn't trigger the error.

[erickt]

@brson pointed out that I was using a rather old form of syntax. When I updated to:

struct Deserializer {
    x: ()
}

impl Deserializer: std::serialization::Deserializer {
    ...
}

it worked. I'll file an issue to get this old syntax removed.