ICE with async function: 'leak-check would have us replace ReStatic with BrAnon(1)'

[pcpthm]

I tried this code Playground. I tried to make this code as minimal as possible.

#![feature(async_await, await_macro, futures_api)]

trait MyClosure {
    type Args;
}
impl<R> MyClosure for dyn FnMut() -> R
where R: 'static {
    type Args = ();
}
struct MyStream<C: ?Sized + MyClosure> {
    x: C::Args,
}
// or get_future() -> futures::future::Ready<()> { futures::future::ready(()) }
async fn get_future<C: ?Sized + MyClosure>(_stream: MyStream<C>) {
}
async fn f() {
    let messages: MyStream<FnMut()> = unimplemented!();
    await!(get_future(messages));
}

Result:

thread 'main' panicked at 'leak-check would have us replace ReStatic with BrAnon(1)', librustc/infer/higher_ranked/mod.rs:763:21
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:480
   6: std::panicking::continue_panic_fmt
             at libstd/panicking.rs:390
   7: std::panicking::begin_panic_fmt
             at libstd/panicking.rs:345
   8: rustc::infer::higher_ranked::<impl rustc::infer::InferCtxt<'a, 'gcx, 'tcx>>::plug_leaks::{{closure}}
   9: <rustc::ty::fold::RegionFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_binder
  10: rustc::ty::fold::TypeFoldable::fold_with
  11: <core::iter::Map<I, F> as core::iter::iterator::Iterator>::fold
  12: rustc::ty::fold::TypeFoldable::fold_with
  13: rustc::infer::higher_ranked::<impl rustc::infer::InferCtxt<'a, 'gcx, 'tcx>>::plug_leaks
  14: rustc::infer::InferCtxt::in_snapshot
  15: <core::iter::FlatMap<I, U, F> as core::iter::iterator::Iterator>::next
  16: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  17: rustc::traits::select::SelectionContext::collect_predicates_for_types
  18: rustc::traits::select::SelectionContext::confirm_candidate
  19: rustc::infer::InferCtxt::probe
  20: rustc::traits::select::SelectionContext::evaluate_stack
  21: rustc::dep_graph::graph::DepGraph::with_anon_task
  22: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  23: rustc::infer::InferCtxt::probe
  24: rustc::traits::select::SelectionContext::evaluate_stack
  25: rustc::dep_graph::graph::DepGraph::with_anon_task
  26: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  27: rustc::infer::InferCtxt::probe
  28: rustc::traits::select::SelectionContext::evaluate_stack
  29: rustc::dep_graph::graph::DepGraph::with_anon_task
  30: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  31: rustc::traits::select::SelectionContext::evaluate_obligation_recursively
  32: rustc::ty::context::tls::with_related_context
  33: rustc::infer::InferCtxtBuilder::enter_with_canonical
  34: rustc_traits::evaluate_obligation::evaluate_obligation
  35: rustc::ty::query::__query_compute::evaluate_obligation
  36: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::evaluate_obligation<'tcx>>::compute
  37: rustc::dep_graph::graph::DepGraph::with_task_impl
  38: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  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::traits::query::evaluate_obligation::<impl rustc::infer::InferCtxt<'cx, 'gcx, 'tcx>>::evaluate_obligation
  42: rustc::traits::query::evaluate_obligation::<impl rustc::infer::InferCtxt<'cx, 'gcx, 'tcx>>::evaluate_obligation_no_overflow
  43: rustc::traits::type_known_to_meet_bound
  44: rustc::ty::context::tls::with_related_context
  45: rustc::infer::InferCtxtBuilder::enter
  46: rustc::ty::util::is_freeze_raw
  47: rustc::ty::query::__query_compute::is_freeze_raw
  48: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::is_freeze_raw<'tcx>>::compute
  49: rustc::dep_graph::graph::DepGraph::with_task_impl
  50: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  51: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  52: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  53: rustc::ty::util::<impl rustc::ty::TyS<'tcx>>::is_freeze
  54: rustc_mir::transform::qualify_consts::Qualifier::new
  55: <rustc_mir::transform::qualify_consts::QualifyAndPromoteConstants as rustc_mir::transform::MirPass>::run_pass
  56: rustc_mir::transform::mir_validated::{{closure}}
  57: rustc_mir::transform::mir_validated
  58: rustc::ty::query::__query_compute::mir_validated
  59: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_validated<'tcx>>::compute
  60: rustc::dep_graph::graph::DepGraph::with_task_impl
  61: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  62: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  63: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  64: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_validated
  65: rustc_mir::borrow_check::mir_borrowck
  66: rustc::ty::query::__query_compute::mir_borrowck
  67: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_borrowck<'tcx>>::compute
  68: rustc::dep_graph::graph::DepGraph::with_task_impl
  69: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  70: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  71: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  72: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_borrowck
  73: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::par_body_owners
  74: rustc::util::common::time
  75: rustc::ty::context::tls::enter_context
  76: <std::thread::local::LocalKey<T>>::with
  77: rustc::ty::context::TyCtxt::create_and_enter
  78: rustc_driver::driver::compile_input
  79: rustc_driver::run_compiler_with_pool
  80: rustc_driver::driver::spawn_thread_pool
  81: rustc_driver::run_compiler
  82: <scoped_tls::ScopedKey<T>>::set
  83: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  84: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  85: rustc_driver::run
  86: rustc_driver::main
  87: std::rt::lang_start::{{closure}}
  88: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  89: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  90: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  91: main
  92: __libc_start_main
  93: <unknown>
query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `[static generator@src/lib.rs:16:14: 19:2 for<'r, 's> {MyStream<(dyn std::ops::FnMut() + 'r)>, impl std::future::Future, ()}]: std::marker::Freeze`
#1 [is_freeze_raw] computing whether `[static generator@src/lib.rs:16:14: 19:2 for<'r, 's> {MyStream<(dyn std::ops::FnMut() + 'r)>, impl std::future::Future, ()}]` is freeze
#2 [mir_validated] processing `f::{{closure}}`
#3 [mir_borrowck] processing `f::{{closure}}`
end of query stack

error: internal compiler error: unexpected panic

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 1.31.0-nightly (4bd4e4130 2018-10-25) 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

[pnkfelix]

This ICE no longer occurs on the nightly compiler.

Marking as E-needs-test so that we don't forget to add a regression test for it.