error: internal compiler error: /checkout/src/librustc/traits/specialize/mod.rs:200: failed to fully normalize <T as Trait<<T as std::iter::Iterator>::Item>>: [FulfillmentError(Obligation(predicate=Binder(TraitPredicate(<T as std::iter::Iterator>)),depth=0),Unimplemented)]

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.23.0-nightly (d762b1d6c 2017-11-04) running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:507:8
stack backtrace:
   0:     0x7fe36602e293 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h9316e6e56004646e
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x7fe366028930 - std::sys_common::backtrace::_print::ha472dcdfa7e3c384
                               at /checkout/src/libstd/sys_common/backtrace.rs:69
   2:     0x7fe36603b5c3 - std::panicking::default_hook::{{closure}}::hab30477517dca11c
                               at /checkout/src/libstd/sys_common/backtrace.rs:58
                               at /checkout/src/libstd/panicking.rs:381
   3:     0x7fe36603b2cd - std::panicking::default_hook::h2a1263edd32fd359
                               at /checkout/src/libstd/panicking.rs:391
   4:     0x7fe36603ba57 - std::panicking::rust_panic_with_hook::ha2112ac7fb330638
                               at /checkout/src/libstd/panicking.rs:577
   5:     0x7fe360c62df7 - std::panicking::begin_panic::hd822aaea2afbdfce
   6:     0x7fe360c7ad01 - rustc_errors::Handler::bug::h1ca171d19938b211
   7:     0x7fe362529ec1 - <std::thread::local::LocalKey<T>>::with::h3f974c8827c95afa
   8:     0x7fe36264d64a - rustc::ty::context::tls::with_opt::h292546ff7edb4d9b
   9:     0x7fe36234c947 - _ZN5rustc7session16opt_span_bug_fmt17h2cde4bbcd3eb8418E.llvm.734E3576
  10:     0x7fe36234c876 - rustc::session::bug_fmt::hffe7f42f13804985
  11:     0x7fe362534a01 - <std::thread::local::LocalKey<T>>::with::he407a4b4ab685ebb
  12:     0x7fe3621c086e - rustc::ty::context::GlobalCtxt::enter_local::h1df032e44e354763
  13:     0x7fe362202e22 - rustc::traits::specialize::specializes::hacfaae44490dcfa2
  14:     0x7fe3626ce359 - rustc::ty::maps::<impl rustc::ty::maps::queries::specializes<'tcx>>::compute_result::h10acbaa712730f30
  15:     0x7fe3624e89b8 - _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17h3e6ba0f04c8cb055E.llvm.C02F9D52
  16:     0x7fe36225d703 - rustc_errors::Handler::track_diagnostics::h71d7340683aa76ff
  17:     0x7fe362179c19 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h06f592214b3f84bb
  18:     0x7fe3626ce3da - _ZN5rustc2ty4maps71_$LT$impl$u20$rustc..ty..maps..queries..specializes$LT$$u27$tcx$GT$$GT$5force17h6864c12eac3cae57E.llvm.13B8F6F0
  19:     0x7fe3626ce9f7 - rustc::ty::maps::<impl rustc::ty::maps::queries::specializes<'tcx>>::try_get::h951fc273275b6802
  20:     0x7fe3622c049e - rustc::ty::maps::TyCtxtAt::specializes::hc43c94fa0fae8954
  21:     0x7fe362536803 - <std::thread::local::LocalKey<T>>::with::heab42bce13f0d3f2
  22:     0x7fe3621c1126 - rustc::ty::context::GlobalCtxt::enter_local::hb5d81b72b8df2044
  23:     0x7fe36235a98d - rustc::traits::specialize::specialization_graph::Graph::insert::hacc9941f6d9b8539
  24:     0x7fe362203f8e - rustc::traits::specialize::specialization_graph_provider::h59a89b46aae590ca
  25:     0x7fe3626bdedf - rustc::ty::maps::<impl rustc::ty::maps::queries::specialization_graph_of<'tcx>>::compute_result::h23185e6c9f3483f3
  26:     0x7fe3624df0d8 - _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17h0efc48a93e7aaebfE.llvm.C02F9D52
  27:     0x7fe36226f859 - rustc_errors::Handler::track_diagnostics::hcc102a9323f0fb95
  28:     0x7fe3621afcb9 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::he4a8687bfebf9a2d
  29:     0x7fe3626bdf73 - rustc::ty::maps::<impl rustc::ty::maps::queries::specialization_graph_of<'tcx>>::force::he57f3bbf5ce29db5
  30:     0x7fe3626be56b - rustc::ty::maps::<impl rustc::ty::maps::queries::specialization_graph_of<'tcx>>::try_get::h0eda24b64c3ab6c7
  31:     0x7fe3622bf6b4 - rustc::ty::maps::TyCtxtAt::specialization_graph_of::he10ae5ce6326cba7
  32:     0x7fe3621c95b3 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::specialization_graph_of::h1fe72663071e7287
  33:     0x7fe364e6bf0c - _ZN12rustc_typeck9coherence14coherent_trait17h734d42f090782304E.llvm.F2765429
  34:     0x7fe3626a0d23 - rustc::ty::maps::<impl rustc::ty::maps::queries::coherent_trait<'tcx>>::compute_result::h73bf4cea46b01c7b
  35:     0x7fe3624e4962 - _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17h2b588360176db9f5E.llvm.C02F9D52
  36:     0x7fe3622553e1 - rustc_errors::Handler::track_diagnostics::h4c1b0e2727a15f6d
  37:     0x7fe3621804c9 - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h20cbeccfef5cd016
  38:     0x7fe3626a0dad - _ZN5rustc2ty4maps74_$LT$impl$u20$rustc..ty..maps..queries..coherent_trait$LT$$u27$tcx$GT$$GT$5force17h378078d7918abe1eE.llvm.13B8F6F0
  39:     0x7fe3626a135d - rustc::ty::maps::<impl rustc::ty::maps::queries::coherent_trait<'tcx>>::try_get::h86bd8d1ce30fce6b
  40:     0x7fe3622bdbb5 - rustc::ty::maps::TyCtxtAt::coherent_trait::hf3cec33d13bac354
  41:     0x7fe3621c8f17 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::coherent_trait::h2a827aff38028239
  42:     0x7fe364e6c7ca - rustc_typeck::coherence::check_coherence::h701a3cfca70e13d1
  43:     0x7fe364eeaeaf - rustc::session::Session::track_errors::hdba8a7f4ad04c402
  44:     0x7fe364f18504 - rustc_typeck::check_crate::h12c7468bcbd5df3b
  45:     0x7fe366455bd8 - <std::thread::local::LocalKey<T>>::with::h930c5aa9ddf86954
  46:     0x7fe36645375c - <std::thread::local::LocalKey<T>>::with::h417ca3b967071686
  47:     0x7fe3663b2931 - rustc::ty::context::TyCtxt::create_and_enter::hc4a7e27debe8252c
  48:     0x7fe3663fea6d - rustc_driver::driver::compile_input::h0f42c21704e17873
  49:     0x7fe366447952 - rustc_driver::run_compiler::h935c8516b4969338
  50:     0x7fe3663d6172 - _ZN3std10sys_common9backtrace28__rust_begin_short_backtrace17h6fc8f1e76a5d872cE.llvm.9ED25DE2
  51:     0x7fe366084bbe - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:99
  52:     0x7fe3663f1b52 - _ZN50_$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$8call_box17h8c9da67e9b2cc9d7E.llvm.9ED25DE2
  53:     0x7fe36603a49b - std::sys::imp::thread::Thread::new::thread_start::h8d440fcc9149eb0b
                               at /checkout/src/liballoc/boxed.rs:772
                               at /checkout/src/libstd/sys_common/thread.rs:24
                               at /checkout/src/libstd/sys/unix/thread.rs:90
  54:     0x7fe3603d0089 - start_thread
  55:     0x7fe365cfe24e - __clone
  56:                0x0 - <unknown>