ICE with bound on struct and reference

[japaric]

STR

trait MatrixRow {}

struct Mat;

impl<'a> MatrixRow for &'a Mat {}

// This `MatrixRow` bound is the ICE trigger
struct Rows<M: MatrixRow> {
    mat: M,
}

impl<'a> Iterator<()> for Rows<&'a Mat> {
    fn next(&mut self) -> Option<()> {
        unimplemented!()
    }
}

fn main() {}

Backtrace

ice.rs:12:1: 16:2 error: internal compiler error: cannot relate bound region: ReInfer(0) <= ReEarlyBound(25, TypeSpace, 0, 'a)
ice.rs:12 impl<'a> Iterator<()> for Rows<&'a Mat> {
ice.rs:13     fn next(&mut self) -> Option<()> {
ice.rs:14         unimplemented!()
ice.rs:15     }
ice.rs:16 }
note: the compiler hit an unexpected failure path. 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
task 'rustc' failed at 'Box<Any>', /var/tmp/paludis/build/dev-lang-rust-scm/work/rust-scm/src/libsyntax/ast_util.rs:776

stack backtrace:
   1:     0x7f2d9ea02cf0 - rt::backtrace::imp::write::hd882173939e2d158lxr
   2:     0x7f2d9ea05dc0 - <unknown>
   3:     0x7f2da2f80a10 - unwind::begin_unwind_inner::h65c561bad0624ee8pie
   4:     0x7f2d9f9cb070 - <unknown>
   5:     0x7f2d9f9cafc0 - diagnostic::SpanHandler::span_bug::h5a0ec8db1633e4bejuF
   6:     0x7f2da37acc00 - driver::session::Session::span_bug::h7c5456bc0ef9253dBnB
   7:     0x7f2da3c8d3b0 - middle::typeck::infer::region_inference::RegionVarBindings<'a>::make_subregion::hde6481d2374d6a2d8v6
   8:     0x7f2da3c73580 - middle::typeck::infer::sub::Sub<'f>.Combine::regions::h410a00df0e5f98a9608
   9:     0x7f2da3c738f0 - middle::typeck::infer::sub::Sub<'f>.Combine::contraregions::h9bdb15d93411a604w08
  10:     0x7f2da3c5d2c0 - middle::typeck::infer::sub::Sub<'f>.Combine::tys::h0e415eeee3a782cdw98
  11:     0x7f2da3ccbb50 - <unknown>
  12:     0x7f2da3c5a910 - <unknown>
  13:     0x7f2da3ccb670 - <unknown>
  14:     0x7f2da3ccb630 - <unknown>
  15:     0x7f2da3c5a910 - <unknown>
  16:     0x7f2da3b55f20 - middle::typeck::infer::mk_eqty::hb30f4823806aa03aX2d
  17:     0x7f2da3b50a10 - <unknown>
  18:     0x7f2da3b4d8a0 - <unknown>
  19:     0x7f2da3b13230 - middle::ty::each_bound_trait_and_supertraits::he39981a7fbf91ecexlJ
  20:     0x7f2da3b4d320 - <unknown>
  21:     0x7f2da3b4b160 - <unknown>
  22:     0x7f2da38a82d0 - middle::typeck::check::vtable::check_param_bounds::hff22d8ef20003549TEN
  23:     0x7f2da38a7fe0 - <unknown>
  24:     0x7f2da3b0f3a0 - <unknown>
  25:     0x7f2da388dad0 - middle::ty::maybe_walk_ty::h22eb602ad62e119cFDF
  26:     0x7f2da389ec50 - <unknown>
  27:     0x7f2da38963e0 - <unknown>
  28:     0x7f2da3899eb0 - middle::kind::check_crate::hc3c3f3a11a49b3325mw
  29:     0x7f2da35ce7b0 - <unknown>
  30:     0x7f2da3e98370 - driver::driver::phase_3_run_analysis_passes::h60371fc635fbafd6lPz
  31:     0x7f2da3e934b0 - driver::driver::compile_input::h41b5be77a886d201rBz
  32:     0x7f2da3f409b0 - <unknown>
  33:     0x7f2da3f408c0 - <unknown>
  34:     0x7f2da3f532f0 - <unknown>
  35:     0x7f2da3f530f0 - <unknown>
  36:     0x7f2da32dcbc0 - <unknown>
  37:     0x7f2da2fd1930 - <unknown>
  38:     0x7f2da2fd1920 - rust_try
  39:     0x7f2da2f7e070 - unwind::try::hb59840f49a9c268eF6d
  40:     0x7f2da2f7de10 - task::Task::run::h16546e7aae493143Zcd
  41:     0x7f2da32dc980 - <unknown>
  42:     0x7f2da2f7fc50 - <unknown>
  43:     0x7f2d9dd7d000 - start_thread
  44:     0x7f2da2c4f269 - clone
  45:                0x0 - <unknown>

Version

rustc 0.12.0-pre (1721e8129 2014-08-18 10:11:03 +0000)

cc @pcwalton