Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/lib.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^

error: internal compiler error: src/librustc/ty/subst.rs:489: Region parameter out of range when substituting in region 'a (root type=Some(&'a str)) (index=0)

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:572:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:478
   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 as rustc::ty::fold::TypeFolder>::fold_region
  15: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  16: <rustc::ty::subst::SubstFolder as rustc::ty::fold::TypeFolder>::fold_ty
  17: rustc::ty::instance::Instance::resolve
  18: <rustc::traits::project::AssociatedTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_const
  19: <smallvec::SmallVec<A> as core::iter::traits::collect::FromIterator<<A as smallvec::Array>::Item>>::from_iter
  20: rustc::ty::fold::TypeFoldable::fold_with
  21: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  22: <rustc::traits::project::AssociatedTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_ty
  23: rustc::traits::project::normalize
  24: rustc_typeck::check::FnCtxt::instantiate_value_path
  25: rustc_typeck::check::FnCtxt::check_expr_kind
  26: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs
  27: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call
  28: rustc_typeck::check::FnCtxt::check_expr_kind
  29: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs
  30: rustc_typeck::check::FnCtxt::check_block_with_expected
  31: rustc_typeck::check::FnCtxt::check_expr_kind
  32: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs
  33: rustc_typeck::check::FnCtxt::check_return_expr
  34: rustc_typeck::check::check_fn
  35: rustc::ty::context::GlobalCtxt::enter_local
  36: rustc_typeck::check::typeck_tables_of
  37: rustc::ty::query::__query_compute::typeck_tables_of
  38: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  39: rustc::dep_graph::graph::DepGraph::with_task_impl
  40: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  41: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  42: rustc_typeck::check::typeck_item_bodies
  43: rustc::ty::query::__query_compute::typeck_item_bodies
  44: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_item_bodies>::compute
  45: rustc::dep_graph::graph::DepGraph::with_task_impl
  46: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  47: rustc::util::common::time
  48: rustc_typeck::check_crate
  49: rustc_interface::passes::analysis
  50: rustc::ty::query::__query_compute::analysis
  51: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute
  52: rustc::dep_graph::graph::DepGraph::with_task_impl
  53: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  54: rustc::ty::context::tls::enter_global
  55: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  56: rustc_interface::passes::create_global_ctxt::{{closure}}
  57: rustc_interface::interface::run_compiler_in_existing_thread_pool
  58: std::thread::local::LocalKey<T>::with
  59: scoped_tls::ScopedKey<T>::set
  60: syntax::with_globals
query stack during panic:
#0 [typeck_tables_of] processing `use_it`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error


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 1.36.0-nightly (a9ec99f42 2019-05-13) running on x86_64-unknown-linux-gnu

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

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

error: Could not compile `playground`.

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