ICE: When implementing trait with a generic parameter and an associated output type

[japaric]

STR

#![feature(associated_types)]

// This was an ICE (#17388), which got fixed by #18868
trait Trait<T> {
    type Output;

    fn fun() -> <Self as Trait<T>>::Output;
}

// The new ICE gets triggered by this `impl`
impl<T> Trait<T> for () {
    type Output = ();

    fn fun() {}
}

fn main() {}

Output

ice.rs:1:1: 1:1 error: internal compiler error: Type parameter `Output/AssocSpace.1` (Output/AssocSpace/1) out of range when substituting (root type=Output) substs=Substs[types=[[T];[()];[()];[]], regions=[[];[];[];[]]]
ice.rs:1 #![feature(associated_types)]
         ^
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
task 'rustc' panicked at 'Box<Any>', /var/tmp/paludis/build/dev-lang-rust-scm/work/rust-scm/src/libsyntax/diagnostic.rs:121

stack backtrace:
   1:     0x7f72dcabfae0 - rt::backtrace::imp::write::hdd602ae028f48d0dvVs
   2:     0x7f72dcac2b70 - <unknown>
   3:     0x7f72dd263310 - unwind::begin_unwind_inner::hbce8e4e8263dca1ePad
   4:     0x7f72da970ac0 - <unknown>
   5:     0x7f72da970a40 - diagnostic::SpanHandler::span_bug::hbe9748378cce230fGYF
   6:     0x7f72dba52970 - middle::subst::SubstFolder<'a, 'tcx>.TypeFolder<'tcx>::fold_ty::h3e05f8a78cf2b146RLP
   7:     0x7f72dbaf3800 - <unknown>
   8:     0x7f72dbaf33b0 - <unknown>
   9:     0x7f72dbaf2af0 - <unknown>
  10:     0x7f72dbb2c5b0 - <unknown>
  11:     0x7f72dbb2c410 - <unknown>
  12:     0x7f72dbb2bf50 - <unknown>
  13:     0x7f72dbb19410 - middle::ty::Generics<'tcx>::to_bounds::h3795ba6b160f5212yd1
  14:     0x7f72dbbe66b0 - middle::typeck::check::wf::BoundsChecker<'cx, 'tcx>::check_trait_ref::ha7aa8a645e91eafdZ9g
  15:     0x7f72dbbe48c0 - <unknown>
  16:     0x7f72dbbe1ae0 - <unknown>
  17:     0x7f72dbbe6c70 - middle::typeck::check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>.Visitor<'v>::visit_item::ha3e9d13b541ef7c6k8g
  18:     0x7f72dbc3bb50 - middle::typeck::check::check_item_types::h754a0f7a04b7367639h
  19:     0x7f72dbfdf590 - <unknown>
  20:     0x7f72dbfde7a0 - middle::typeck::check_crate::h03aa0a74283c33108PL
  21:     0x7f72dd75bcc0 - driver::driver::phase_3_run_analysis_passes::h13d5815dc0529392D5R
  22:     0x7f72dd750ae0 - driver::driver::compile_input::hce9f8a5af8c23ae8nMR
  23:     0x7f72dd7d51d0 - <unknown>
  24:     0x7f72dd7d50c0 - <unknown>
  25:     0x7f72dd5e2d50 - <unknown>
  26:     0x7f72dd5e2b40 - <unknown>
  27:     0x7f72ddaf4ba0 - <unknown>
  28:     0x7f72dd2b2670 - <unknown>
  29:     0x7f72dd2b2660 - rust_try
  30:     0x7f72dd260c70 - unwind::try::hc967dd74749deb3arZc
  31:     0x7f72dd260b00 - task::Task::run::h236da885853fa0e4h5b
  32:     0x7f72ddaf48e0 - <unknown>
  33:     0x7f72dd262320 - <unknown>
  34:     0x7f72d7d451d0 - start_thread
  35:     0x7f72dcf391b9 - clone
  36:                0x0 - <unknown>

Version

#19113 + #18868 on top of bfaa7bc

cc @nikomatsakis

[tomjakubowski]

On version b825b34 I get this ICE just with (edited with a smaller example):

#![feature(associated_types)]
#![crate_type="lib"]

pub trait Foo<A> {
    type B;

    fn foo(&self) -> bool { false }
}

foo.rs:1:1: 1:1 error: internal compiler error: Type parameter `B/AssocSpace.1` (B/AssocSpace/1) out of range when substituting (root type=B) substs=Substs[types=[[A];[Self];[B];[]], regions=[[];[];[];[]]]
foo.rs:1 #![feature(associated_types)]
         ^
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
task 'rustc' panicked at 'Box<Any>', /home/tom/src/rust/rust/src/libsyntax/diagnostic.rs:121

stack backtrace:
   1:     0x7f42b15e5750 - rt::backtrace::imp::write::hd4dc9c5b7adc70deB9s
   2:     0x7f42b15e88f0 - failure::on_fail::h601ae62da37820fduwt
   3:     0x7f42b1d8b5b0 - unwind::begin_unwind_inner::hd5e2a13fc766a9ednbd
   4:     0x7f42af488b30 - unwind::begin_unwind::h1840779095798302194
   5:     0x7f42af488ab0 - diagnostic::SpanHandler::span_bug::haca8008c8efcaccdl7F
   6:     0x7f42b05766a0 - middle::subst::SubstFolder<'a, 'tcx>.TypeFolder<'tcx>::fold_ty::h6dfb50fd9b2a318dKTP
   7:     0x7f42b0617f80 - middle::ty_fold::VecPerParamSpace<T>.TypeFoldable<'tcx>::fold_with::closure.96163
   8:     0x7f42b0617b30 - middle::subst::VecPerParamSpace<T>::map_enumerated::h1858619917310266163
   9:     0x7f42b0617270 - middle::ty_fold::TypeFolder::fold_substs::h10218276810570421665
  10:     0x7f42b0650d50 - middle::ty_fold::Vec<T>.TypeFoldable<'tcx>::fold_with::closure.98606
  11:     0x7f42b0650bb0 - vec::Vec<T>.FromIterator<T>::from_iter::h15054265504360828229
  12:     0x7f42b06506f0 - middle::ty_fold::ty..ParamBounds<'tcx>.TypeFoldable<'tcx>::fold_with::h5912314470836935956
  13:     0x7f42b063db90 - middle::ty::Generics<'tcx>::to_bounds::hbca748b7f43f8696vo1
  14:     0x7f42b0652470 - middle::ty::construct_parameter_environment::he8cb628e2da26785Gy6
  15:     0x7f42b0651dd0 - middle::ty::ParameterEnvironment<'tcx>::for_item::haae90d8e2fdf61c2ju1
  16:     0x7f42b071ef30 - middle::typeck::check::check_method_body::he4cebab5fe2fb8f8nwi
  17:     0x7f42b07134a0 - middle::typeck::check::check_item::h2db4e12f763145a7vli
  18:     0x7f42b0717350 - middle::typeck::check::check_item_types::h6c8b3f561b623f38x0h
  19:     0x7f42b0b03fa0 - util::common::time::h16216271059762254987
  20:     0x7f42b0b031b0 - middle::typeck::check_crate::hd1db30e85ca4d877jVL
  21:     0x7f42b2298aa0 - driver::driver::phase_3_run_analysis_passes::h27f0c337e17ae602bfS
  22:     0x7f42b228d8c0 - driver::driver::compile_input::h144d59d4a02adda6VVR
  23:     0x7f42b2312840 - driver::run_compiler::h0f9dd69b80cf00c4pUT
  24:     0x7f42b2312730 - driver::run::closure.59734
  25:     0x7f42b211ef60 - task::TaskBuilder<S>::try_future::closure.39040
  26:     0x7f42b211ed50 - task::TaskBuilder<S>::spawn_internal::closure.39011
  27:     0x7f42b2632a40 - task::NativeSpawner.Spawner::spawn::closure.2471
  28:     0x7f42b1dedc60 - rust_try_inner
  29:     0x7f42b1dedc50 - rust_try
  30:     0x7f42b1d88f10 - unwind::try::hbf9691835cc163a4IZc
  31:     0x7f42b1d88da0 - task::Task::run::h309f69a6701379ady5b
  32:     0x7f42b2632780 - task::NativeSpawner.Spawner::spawn::closure.2397
  33:     0x7f42b1d8a5c0 - thread::thread_start::h721d15c10ff33d0aEqc
  34:     0x7f42ac7f9250 - start_thread
  35:     0x7f42b1a613b9 - clone
  36:                0x0 - <unknown>