Impls of traits with associated types don't work cross crate

[sfackler]

foo.rs:

#![feature(associated_types)]

pub trait T {
    type C;
}

main.rs:

#![feature(associated_types)]
extern crate foo;

struct Foo;

impl foo::T for Foo {
    type C = ();
}

fn main() {}

~ ❯ env RUST_BACKTRACE=1 rustc -L. test.rs
ERROR:rbml::reader: failed to find block with tag 2
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'explicit panic', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/librbml/lib.rs:253

stack backtrace:
   1:        0x104a5b1e5 - sys::backtrace::write::h4cebc8c3e368e8f0Upt
   2:        0x104a7fc33 - failure::on_fail::hd9de93a6058d1a7dwwz
   3:        0x1049e5e6a - rt::unwind::begin_unwind_inner::h00d5ebf844629bb50dz
   4:        0x1030c74db - rt::unwind::begin_unwind::h4125333724720779177
   5:        0x1030c60e4 - reader::get_doc::h76807416f04bf0f7bLa
   6:        0x1021729d4 - metadata::decoder::item_def_id::h2bfb567a68e455cbj6h
   7:        0x1021b95aa - metadata::decoder::get_impl_or_trait_item::h7f439d8f2829cb421Ui
   8:        0x1021661c4 - metadata::csearch::get_impl_or_trait_item::hf3d420b16148eb58e8k
   9:        0x101ffc311 - middle::ty::impl_or_trait_item::h2355a4845ecaf3fciw7
  10:        0x10216466b - middle::ty::trait_items::h2db0d9abf50e4ccdZu7
  11:        0x1019b9846 - check::check_item::hac3080059fe09f34SSj
  12:        0x101b4ce40 - check_crate::unboxed_closure.39832
  13:        0x101b48733 - check_crate::h127b3439cfd8ff83NLx
  14:        0x101363d52 - driver::phase_3_run_analysis_passes::hadc5fda84afbf325qva
  15:        0x101350b88 - driver::compile_input::h9d2d7dddc58375d9wba
  16:        0x101482843 - thunk::F.Invoke<A, R>::invoke::h1922614042677645733
  17:        0x10147f9a0 - rt::unwind::try::try_fn::h5185751407680132505
  18:        0x104ae75e9 - rust_try_inner
  19:        0x104ae75d6 - rust_try
  20:        0x1014800e6 - thunk::F.Invoke<A, R>::invoke::h18183949975069308340
  21:        0x104a6c544 - sys::thread::thread_start::h0fb21aaa7cc37e0dDfw
  22:     0x7fff8dd8c2fc - _pthread_body
  23:     0x7fff8dd8c279 - _pthread_body

rustc 0.13.0-nightly (7608dbad6 2014-12-31 10:06:21 -0800)

[sfackler]

cc @nikomatsakis @nick29581

[japaric]

This has already been fixed in #20374

[nikomatsakis]

Good to have a test though. As I recall we didn't make one.