Internal compiler error: Implementation missing trait type parameter panics compiler

[araujol]

When trying to compile the following code snippet from the project rust-efl:

impl<'r, T> Iterator for EinaList<'r, T> {
    fn next(&mut self) -> Option<&'r T> {
        let v = list_data_get(self._eo);
        *self = match list_next(self._eo) {
            None => EinaList { _eo: ptr::null_mut() },
            Some(l) => EinaList { _eo: l }
        };
        return v
    }
}

The compiler throws the following error (backtrace included):

src/eio.rs:27:3: 27:18 warning: `deriving` is deprecated; use `derive`
src/eio.rs:27 #[deriving(Show)]
                ^~~~~~~~~~~~~~~
src/eet.rs:69:3: 69:33 warning: `deriving` is deprecated; use `derive`
src/eet.rs:69 #[deriving(Show, FromPrimitive)]
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/eina.rs:196:1: 207:2 error: internal compiler error: impl `VtableImpl(impl_def_id=DefId { krate: 0, node: 2766 }:eina::EinaList<'r, T>.Iterator, substs=Substs[types=[[_];[];[]], regions=[['_#0r];[];[]]], nested=[[Obligation(predicate=Binder(TraitPredicate(TraitRef(T, core::kinds::Sized))),depth=1)];[];[]])` did not contain projection for `Obligation(predicate=<eina::EinaList<'r, T> as TraitRef(eina::EinaList<'r, T>, core::iter::Iterator)>::Item,depth=0)`
src/eina.rs:196 impl<'r, T> Iterator for EinaList<'r, T> {
src/eina.rs:197 
src/eina.rs:198     fn next(&mut self) -> Option<&'r T> {
src/eina.rs:199         let v = list_data_get(self._eo);
src/eina.rs:200         *self = match list_next(self._eo) {
src/eina.rs:201             None => EinaList { _eo: ptr::null_mut() },
                ...
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 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:123

stack backtrace:
   1: 0x40233e30 - sys::backtrace::write::hd07b456e2fb2edc64it
   2: 0x40258680 - failure::on_fail::hc26c935da551c95azvz
   3: 0x401c0c10 - rt::unwind::begin_unwind_inner::he25945c8d3f9a8c2eaz
   4: 0x43c32c60 - rt::unwind::begin_unwind::h5827585231859819369
   5: 0x43c32bd0 - diagnostic::SpanHandler::span_bug::h9f9dede6a55a96f0DFF
   6: 0x4133ad30 - middle::traits::project::project_type::h2397f2bdf09c070052P
   7: 0x41337e20 - middle::traits::project::opt_normalize_projection_type::h9840021934a72d668UP
   8: 0x41326640 - middle::traits::project::normalize_projection_type::h784de1d4a68f87bfJTP
   9: 0x413391c0 - middle::traits::project::AssociatedTypeNormalizer<'a, 'b, 'tcx>.TypeFolder<'tcx>::fold_ty::h93dc24df4c299e53kSP
  10: 0x4078b870 - middle::ty_fold::Rc<T>.TypeFoldable<'tcx>::fold_with::h14798399643135356730
  11: 0x4078c460 - middle::ty_fold::VecPerParamSpace<T>.TypeFoldable<'tcx>::fold_with::h9678217035264924423
  12: 0x407a85c0 - check::FnCtxt<'a, 'tcx>::instantiate_bounds::h965cba437f15b636Oll
  13: 0x407c1050 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>::check_impl::closure.29994
  14: 0x407bd180 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>::with_fcx::h551410613b5bc2f0Gfi
  15: 0x407c3d40 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>.Visitor<'v>::visit_item::h42e9f9bd2e45c68esoi
  16: 0x407c58c0 - visit::walk_mod::h8273770565610179432
  17: 0x407c3d40 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>.Visitor<'v>::visit_item::h42e9f9bd2e45c68esoi
  18: 0x409cad20 - check_crate::unboxed_closure.40159
  19: 0x409c5560 - check_crate::h1a6ec5dffa2bd3a7jsx
  20: 0x40060dc0 - driver::phase_3_run_analysis_passes::hdf5c0700c25562beTva
  21: 0x4004ee90 - driver::compile_input::hc6337ba6b18bc0dewba
  22: 0x40121170 - thunk::F.Invoke<A, R>::invoke::h8973449830402138319
  23: 0x4011ff80 - rt::unwind::try::try_fn::h4951350354602804749
  24: 0x402c8ba0 - rust_try_inner
  25: 0x402c8b70 - rust_try
  26: 0x401202c0 - thunk::F.Invoke<A, R>::invoke::h9098173034894979218
  27: 0x402455d0 - sys::thread::thread_start::h92aa6f5030fe4b1ca9v
  28: 0x443d1ea0 - start_thread
  29: 0x4063c472 - clone
  30:        0x0 - <unknown>

make: *** [libefl.rlib] Error 101

rustc version:

rustc 0.13.0-nightly (c6c786671 2015-01-04 00:50:59 +0000)
binary: rustc
commit-hash: c6c786671d692d7b13c2e5c68a53001327b4b125
commit-date: 2015-01-04 00:50:59 +0000
host: i686-unknown-linux-gnu
release: 0.13.0-nightly

[japaric]

I think this is a duplicate of #20532. You need to add the output type to your Iterator impl:

impl<'r, T> Iterator for EinaList<'r, T> {
    type Output = &'r T;

    fn next(&mut self) -> Option<&'r T> {
        // ...
    }
}

[araujol]

Thanks!

After checking around some Iterator implementations, the correct type is Item, this actually makes the compiler pass:

type Item = &'r T;

[huonw]

Closing as a dupe of #20347, thanks for filing!