ICE with HRTB and lifetime on subtrait

[alecmocatta]

I'm using a lifetime parameter on a trait such that I can constrain Item to for <'a> &'a X. I tried to "encapsulate" the lifetime into a subtrait to avoid other issues and got an ICE on stable, nightly and with/without NLL. I suspect this usage should error but I could be mistaken.

trait Sink {
    type Item;
    fn next(&mut self, Self::Item);
}
trait SinkA<'a>: Sink {}

struct X(u8);

fn abc<I>(mut i: I) where for<'a> I: SinkA<'a, Item=&'a X> {
    let x = X(0);
    i.next(&x);
}

(Playground)

error: internal compiler error: librustc/infer/higher_ranked/mod.rs:160: no representative region for `ReSkolemized(UniverseIndex(1), BrNamed(crate0:DefIndex(1:13), 'a))` in `{ReSkolemized(UniverseIndex(1), BrNamed(crate0:DefIndex(1:13), 'a))}`

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:554:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:515
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::session::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::session::opt_span_bug_fmt
  13: rustc::session::bug_fmt
  14: rustc::infer::higher_ranked::<impl rustc::infer::combine::CombineFields<'a, 'gcx, 'tcx>>::higher_ranked_match::{{closure}}::{{closure}}::{{closure}}
  15: <std::collections::hash::map::HashMap<K, V, S> as core::iter::traits::FromIterator<(K, V)>>::from_iter
  16: rustc::infer::InferCtxt::commit_if_ok
  17: rustc::infer::InferCtxt::match_poly_projection_predicate
  18: rustc::traits::project::confirm_param_env_candidate
  19: rustc::traits::project::opt_normalize_projection_type
  20: rustc::traits::project::normalize_projection_type
  21: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  22: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  23: rustc::ty::fold::TypeFoldable::fold_with
  24: rustc::ty::fold::TypeFoldable::fold_with
  25: rustc::traits::project::normalize
  26: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  27: <core::iter::FlatMap<I, U, F> as core::iter::iterator::Iterator>::next
  28: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  29: rustc::ty::wf::WfPredicates::normalize
  30: rustc::ty::wf::predicate_obligations
  31: rustc_typeck::check::wfcheck::check_where_clauses
  32: rustc_typeck::check::wfcheck::check_fn_or_method
  33: rustc::ty::context::tls::with_related_context
  34: rustc::infer::InferCtxtBuilder::enter
  35: rustc_typeck::check::wfcheck::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::context::tls::with_related_context
  39: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  40: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  41: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query
  42: rustc::hir::Crate::visit_all_item_likes
  43: rustc::session::Session::track_errors
  44: rustc::util::common::time
  45: rustc_typeck::check_crate
  46: rustc::ty::context::tls::enter_context
  47: <std::thread::local::LocalKey<T>>::with
  48: rustc::ty::context::TyCtxt::create_and_enter
  49: rustc_driver::driver::compile_input
  50: rustc_driver::run_compiler_with_pool
  51: <scoped_tls::ScopedKey<T>>::set
  52: syntax::with_globals
  53: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  54: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  55: rustc_driver::run
  56: rustc_driver::main
  57: std::rt::lang_start::{{closure}}
  58: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  59: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  60: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  61: main
  62: __libc_start_main
  63: <unknown>
query stack during panic:
#0 [check_item_well_formed] processing `abc`
end of query stackerror: aborting due to previous error

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

note: rustc 1.28.0 (9634041f0 2018-07-30) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type lib

[earthengine]

Minimum reproducable:

trait MyF<'a>: FnOnce() -> &'a () {}

fn test<F>(_: F) where for<'a> F: MyF<'a, Output=&'a ()> {
}

fn main(){
}

Note: This bug depends on the need to specify an associate type in the super trait, with a lifetime. Then, in the trait bound where clause, specify the associate type explicitly.

[alecmocatta]

To aid searchability here's the slightly different error from latest nightly. The backtrace is largely identical.

error: internal compiler error: librustc/infer/higher_ranked/mod.rs:162: no representative region for `RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:13), 'a) })` in `{RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:13), 'a) })}`

[cyplo]

The minimum reproducable still ICEs on stable - rustc 1.32.0 (9fda7c2 2019-01-16).
Seems fixed on beta (1.33.0-beta.4)

[alecmocatta]

Closing as fixed on beta & nightly. Thanks wonderful member(s) of the rust community that resolved this!