GAT ICE, without using the GAT feature

[remexre]

Building the ecs crate (libs/ecs) of 3fab9cb3890cff565d4dbedd9b320d6b49dd4d48 of https://github.com/remexre/ia gets the following ICE:

$ rustc --version
rustc 1.34.0 (91856ed52 2019-04-10)

$ cargo check
    Checking ecs v0.1.0 (/home/nathan/Projects/ia/libs/ecs)
error[E0658]: generic associated types are unstable (see issue #44265)
  --> libs/ecs/src/component_store.rs:81:5
   |
81 |     type Out<'a>;
   |     ^^^^^^^^^^^^^

error[E0658]: generic associated types are unstable (see issue #44265)
  --> libs/ecs/src/component_store.rs:85:5
   |
85 |     type Out<'a> = HCons<&'a H, T>;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0658]: generic associated types are unstable (see issue #44265)
  --> libs/ecs/src/component_store.rs:89:5
   |
89 |     type Out<'a> = Hlist![Entity];
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: src/librustc/ty/subst.rs:426: Region parameter out of range when substituting in region 'a (root type=Some
(frunk_core::hlist::HCons<&'a H, T>)) (index=2)

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:558:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::span_bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::span_bug_fmt
  14: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_region
  15: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  16: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  17: <smallvec::SmallVec<A> as core::iter::traits::collect::FromIterator<<A as smallvec::Array>::Item>>::from_iter
  18: rustc::ty::fold::TypeFoldable::fold_with
  19: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  20: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  21: rustc::traits::project::opt_normalize_projection_type
  22: rustc::traits::project::normalize_projection_type
  23: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  24: <smallvec::SmallVec<A> as core::iter::traits::collect::FromIterator<<A as smallvec::Array>::Item>>::from_iter
  25: rustc::ty::fold::TypeFoldable::fold_with
  26: rustc::ty::fold::TypeFoldable::fold_with
  27: rustc::ty::fold::TypeFoldable::fold_with
  28: rustc::traits::project::normalize
  29: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
  30: <core::iter::adapters::flatten::FlatMap<I, U, F> as core::iter::traits::iterator::Iterator>::next
  31: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  32: rustc::ty::wf::trait_obligations
  33: rustc::ty::context::GlobalCtxt::enter_local
  34: rustc_typeck::check::wfcheck::check_item_well_formed
  35: rustc::ty::query::__query_compute::check_item_well_formed
  36: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>:
:compute
  37: rustc::dep_graph::graph::DepGraph::with_task_impl
  38: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  39: rustc::hir::Crate::visit_all_item_likes
  40: rustc::util::common::time
  41: rustc_typeck::check_crate
  42: <std::thread::local::LocalKey<T>>::with
  43: rustc::ty::context::TyCtxt::create_and_enter
  44: rustc_driver::driver::compile_input
  45: rustc_driver::run_compiler_with_pool
  46: <scoped_tls::ScopedKey<T>>::set
  47: rustc_driver::run_compiler
  48: syntax::with_globals
  49: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:87
  50: <F as alloc::boxed::FnBox<A>>::call_box
  51: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/91856ed52c58aa5ba66a015354d1cc69e9779bdf/src/liballoc/boxed.rs:759
             at src/libstd/sys_common/thread.rs:14
             at src/libstd/sys/unix/thread.rs:81
  52: <unknown>
             at /usr/src/debug/sys-libs/glibc-2.28-r6/glibc-2.28/nptl/pthread_create.c:486
  53: clone
             at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
query stack during panic:
#0 [check_item_well_formed] processing `<frunk_core::hlist::HCons<H, T> as component_store::IterComponents>`
end of query stack
error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0658`.

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 1.34.0 (91856ed52 2019-04-10) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `ecs`.

To learn more, run the command again with --verbose.

[hellow554]

Reduced Example:

trait Foo {}
struct Bar<H>(std::marker::PhantomData<H>);

pub trait Baz {
    type Out<'a>;
}

impl<H: Foo> Baz for Bar<H> {
    type Out<'a> = Bar<&'a H>;
}

[hellow554]

Bug was introduced between 68fe518...b92552d

Bisecting shows bug was introduced in b92552d

CC #57272 ping @petrochenkov

[petrochenkov]

#57272 rather uncovered the issue than introduced it.

Semi-implemented features should issue errors rather than ICEs regardless of presence or absence of #![feature(...)].

[hellow554]

rather uncovered the issue than introduced

True.. sorry for that :|

Yep, that's right. Even nightly-2018-01-01 panicks with the same ICE. So this was there forever.

[jonas-schievink]

Small reproduction from #60477:

pub trait Foo<T> {
    type Iter<'a>: Iterator<Item=&'a T>;
}

yields:

error[E0658]: generic associated types are unstable (see issue #44265)
 --> src/lib.rs:2:5
  |
2 |     type Iter<'a>: Iterator<Item=&'a T>;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: src/librustc/ty/subst.rs:426: Region parameter out of range when substituting in region 'a (root type=Some(&'a T)) (index=2)

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:558:9
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
error: aborting due to 2 previous errors

[jonas-schievink]

This issue is also a duplicate of #58694, so closing in favor of that