ICE when computing the size of a specialized associated trait type

[mjbshaw]

The following code creates a trait (creatively named Trait) that has an associated type (creatively named Type). An default implementation of this trait is given for all types, with Type = [u8; 1]. Specializing the trait (for *const T, for example) works, except that doing size_of::<<T as Trait>::Type>() causes an ICE.

(Playground link)

#![feature(specialization)]

pub trait Trait {
  type Type;
}

impl<T: ?Sized> Trait for T {
  default type Type = [u8; 1];
}

impl<T: Trait> Trait for *const T {
  type Type = [u8; std::mem::size_of::<<T as Trait>::Type>()];
}

Expected behavior: I believe this code should compile just fine, with *const T's Trait::Type being equivalent to to T's Trait::Type.

Actual behavior: ICE: error: internal compiler error: librustc/ty/subst.rs:479: Type parameter T/#0 (T/0) out of range when substituting (root type=Some(fn() -> usize {std::mem::size_of::<<T as Trait>::Type>})) substs=[]

Rust version: rustc --version --verbose:

rustc 1.28.0-nightly (cd494c1f0 2018-06-27)
binary: rustc
commit-hash: cd494c1f0915da00a63c03454a96d504afe764ff
commit-date: 2018-06-27
host: x86_64-apple-darwin
release: 1.28.0-nightly
LLVM version: 6.0

Backtrace:

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:499:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::span_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::span_bug_fmt
  14: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  15: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  16: rustc::ty::fold::TypeFoldable::fold_with
  17: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  18: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  19: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  20: rustc::ty::fold::TypeFoldable::fold_with
  21: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  22: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  23: <rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::eval_operand
  24: rustc_mir::interpret::terminator::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::eval_terminator
  25: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::step
  26: rustc_mir::interpret::const_eval::eval_body_using_ecx
  27: rustc_mir::interpret::const_eval::const_eval_provider
  28: rustc::ty::query::__query_compute::const_eval
  29: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::const_eval<'tcx>>::compute
  30: rustc::ty::context::tls::with_context
  31: rustc::dep_graph::graph::DepGraph::with_task_impl
  32: rustc::ty::context::tls::with_related_context
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  34: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  35: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const
  36: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  37: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  38: rustc::traits::project::opt_normalize_projection_type
  39: rustc::traits::project::normalize_projection_type
  40: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  41: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  42: rustc::ty::fold::TypeFoldable::fold_with
  43: rustc::ty::fold::TypeFoldable::fold_with
  44: rustc::ty::fold::TypeFoldable::fold_with
  45: rustc::traits::project::normalize
  46: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  47: <core::iter::FlatMap<I, U, F> as core::iter::iterator::Iterator>::next
  48: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  49: rustc::ty::wf::WfPredicates::normalize
  50: rustc::ty::wf::trait_obligations
  51: rustc::ty::context::tls::with_related_context
  52: rustc::infer::InferCtxtBuilder::enter
  53: rustc_typeck::check::wfcheck::check_item_well_formed
  54: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>::compute
  55: rustc::ty::context::tls::with_context
  56: rustc::dep_graph::graph::DepGraph::with_task_impl
  57: rustc::ty::context::tls::with_related_context
  58: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  59: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  60: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query
  61: rustc::hir::Crate::visit_all_item_likes
  62: rustc::session::Session::track_errors
  63: rustc::util::common::time
  64: rustc_typeck::check_crate
  65: rustc::ty::context::tls::enter_context
  66: <std::thread::local::LocalKey<T>>::with
  67: rustc::ty::context::TyCtxt::create_and_enter
  68: rustc_driver::driver::compile_input
  69: rustc_driver::run_compiler_with_pool
  70: <scoped_tls::ScopedKey<T>>::set
  71: syntax::with_globals
  72: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  73: __rust_maybe_catch_panic
  74: rustc_driver::run
  75: rustc_driver::main
  76: std::rt::lang_start::{{closure}}
  77: std::panicking::try::do_call
  78: __rust_maybe_catch_panic
  79: std::rt::lang_start_internal
  80: main
query stack during panic:
#0 [const_eval] const-evaluating `<*const T as TypeEncoding>::Type::{{constant}}`
#1 [check_item_well_formed] processing `<*const T as TypeEncoding>`
end of query stack

[mjbshaw]

This looks related to #43408 (see in particular MageSlayer's comment).

[JohnTitor]

Triage:
This is no longer ICE with the latest nightly: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=76f84478a83b3a63284a65e0b3580c35