ICE cause by tokio::spawn a async function return future opaque type

[shisoft]

The ICE cause by cargo check, seems happened in multiple locations. One of the cause is when calling tokio::spawn function.

I don't know how to reproduce this problem in minimal example, but the faulty code in my project comes from here
https://github.com/ShisoftResearch/bifrost/blob/f67c57209dd15072a2868f46c1d26cd356caafae/src/raft/mod.rs#L631

Expecting the code to compile or providing reason for the failure. Instead, the compile just crashed.
This problem appears on both MacOS and Linux

Meta

rustc 1.42.0-nightly (5e8897b 2020-01-21)
binary: rustc
commit-hash: 5e8897b
commit-date: 2020-01-21
host: x86_64-unknown-linux-gnu
release: 1.42.0-nightly
LLVM version: 9.0

tokio 0.2.10

Backtrace:

error: internal compiler error: src/librustc/ich/impls_ty.rs:96: StableHasher: unexpected region RePlaceholder(Placeholder { universe: U596, name: BrAnon(3) })

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:882:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1052
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1426
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:204
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:224
  10: rustc_driver::report_ice
  11: <alloc::boxed::Box<F> as core::ops::function::Fn<A>>::call
             at /rustc/5e8897b7b51636f157630e6639b711d698e1d101/src/liballoc/boxed.rs:1029
  12: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}::{{closure}}
             at /rustc/5e8897b7b51636f157630e6639b711d698e1d101/src/libproc_macro/bridge/client.rs:305
  13: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:476
  14: std::panicking::begin_panic
  15: rustc_errors::HandlerInner::bug
  16: rustc_errors::Handler::bug
  17: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  18: rustc::ty::context::tls::with_opt::{{closure}}
  19: rustc::ty::context::tls::with_opt
  20: rustc::util::bug::opt_span_bug_fmt
  21: rustc::util::bug::bug_fmt
  22: rustc::ich::impls_ty::<impl rustc_data_structures::stable_hasher::HashStable<rustc::ich::hcx::StableHashingContext> for rustc::ty::sty::RegionKind>::hash_stable
  23: rustc::ty::sty::_DERIVE_rustc_data_structures_stable_hasher_HashStable_rustc_ich_StableHashingContext_ctx_FOR_TyKind::<impl rustc_data_structures::stable_hasher::HashStable<rustc::ich::hcx::StableHashingContext> for rustc::ty::sty::TyKind>::hash_stable
  24: std::thread::local::LocalKey<T>::with
  25: rustc::ty::sty::_DERIVE_rustc_data_structures_stable_hasher_HashStable_rustc_ich_StableHashingContext_ctx_FOR_TyKind::<impl rustc_data_structures::stable_hasher::HashStable<rustc::ich::hcx::StableHashingContext> for rustc::ty::sty::TyKind>::hash_stable
  26: std::thread::local::LocalKey<T>::with
  27: rustc::mir::interpret::_DERIVE_rustc_data_structures_stable_hasher_HashStable_rustc_ich_StableHashingContext_ctx_FOR_GlobalId::<impl rustc_data_structures::stable_hasher::HashStable<rustc::ich::hcx::StableHashingContext> for rustc::mir::interpret::GlobalId>::hash_stable
  28: <T as rustc::dep_graph::dep_node::DepNodeParams>::to_fingerprint
  29: rustc::dep_graph::dep_node::DepNode::new
  30: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  31: rustc::mir::interpret::queries::<impl rustc::ty::context::TyCtxt>::const_eval_instance
  32: rustc::mir::interpret::queries::<impl rustc::ty::context::TyCtxt>::const_eval_resolve
  33: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_const
  34: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  35: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_ty
  36: rustc::traits::project::normalize_with_depth
  37: rustc::infer::InferCtxt::commit_unconditionally
  38: <core::iter::adapters::flatten::FlatMap<I,U,F> as core::iter::traits::iterator::Iterator>::next
  39: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  40: rustc::traits::select::SelectionContext::collect_predicates_for_types
  41: rustc::traits::select::SelectionContext::confirm_candidate
  42: rustc::traits::select::SelectionContext::select
  43: rustc_data_structures::obligation_forest::ObligationForest<O>::process_obligations
  44: <rustc::traits::fulfill::FulfillmentContext as rustc::traits::engine::TraitEngine>::select_where_possible
  45: rustc_typeck::check::FnCtxt::check_argument_types
  46: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::confirm_builtin_call
  47: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call
  48: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  49: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  50: rustc_typeck::check::FnCtxt::check_decl_initializer
  51: rustc_typeck::check::FnCtxt::check_decl_local
  52: rustc_typeck::check::FnCtxt::check_stmt
  53: rustc_typeck::check::FnCtxt::check_block_with_expected
  54: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  55: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  56: rustc_typeck::check::FnCtxt::check_stmt
  57: rustc_typeck::check::FnCtxt::check_block_with_expected
  58: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  59: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  60: rustc_typeck::check::_match::<impl rustc_typeck::check::FnCtxt>::check_match
  61: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  62: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  63: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  64: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  65: rustc_typeck::check::FnCtxt::check_stmt
  66: rustc_typeck::check::FnCtxt::check_block_with_expected
  67: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  68: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  69: rustc_typeck::check::_match::<impl rustc_typeck::check::FnCtxt>::check_match
  70: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  71: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  72: rustc_typeck::check::FnCtxt::check_block_with_expected
  73: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  74: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  75: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  76: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  77: rustc_typeck::check::FnCtxt::check_block_with_expected
  78: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  79: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  80: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  81: rustc_typeck::check::check_fn
  82: rustc_typeck::check::closure::<impl rustc_typeck::check::FnCtxt>::check_expr_closure
  83: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  84: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  85: rustc_typeck::check::FnCtxt::check_argument_types
  86: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::confirm_builtin_call
  87: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call
  88: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  89: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  90: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  91: rustc_typeck::check::check_fn
  92: rustc::ty::context::tls::with_context::{{closure}}
  93: rustc_typeck::check::typeck_tables_of
  94: rustc::ty::query::__query_compute::typeck_tables_of
  95: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  96: rustc::dep_graph::graph::DepGraph::with_task_impl
  97: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  98: rustc_typeck::collect::type_of
  99: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::type_of>::compute
 100: rustc::dep_graph::graph::DepGraph::with_task_impl
 101: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
 102: rustc::traits::select::SelectionContext::constituent_types_for_ty
 103: rustc::ty::sty::Binder<T>::map_bound
 104: rustc::traits::select::SelectionContext::confirm_candidate
 105: rustc::infer::InferCtxt::probe
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.42.0-nightly (5e8897b7b 2020-01-21) 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

query stack during panic:
#0 [typeck_tables_of] processing `raft::RaftService::send_followers_heartbeat`
#1 [type_of] processing `raft::RaftService::send_followers_heartbeat::{{opaque}}#0`
#2 [evaluate_obligation] evaluating trait selection obligation `for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6, 't7, 't8, 't9, 't10, 't11, 't12, 't13, 't14, 't15, 't16, 't17, 't18, 't19, 't20, 't21, 't22, 't23> {std::sync::Arc<raft::RaftService>, i64, i64, raft::RaftService, std::sync::Arc<raft::RaftService>, &'r utils::rwlock::RwLock<raft::RaftMeta>, utils::rwlock::RwLock<raft::RaftMeta>, utils::rwlock::RwLockWriteGuardFut<'s, raft::RaftMeta>, utils::rwlock::RwLockWriteGuardFut<'t0, raft::RaftMeta>, (), (), utils::rwlock::RwLockWriteGuard<'t1, raft::RaftMeta>, raft::CheckerAction, raft::CheckerAction, &'t2 raft::RaftService, std::sync::Arc<raft::RaftService>, utils::rwlock::RwLockWriteGuard<'t3, raft::RaftMeta>, &'t4 mut utils::rwlock::RwLockWriteGuard<'t5, raft::RaftMeta>, &'t6 mut utils::rwlock::RwLockWriteGuard<'t7, raft::RaftMeta>, std::option::Option<u64>, impl core::future::future::Future, impl core::future::future::Future, (), (), &'t14 raft::RaftService, std::sync::Arc<raft::RaftService>, utils::rwlock::RwLockWriteGuard<'t15, raft::RaftMeta>, &'t16 mut utils::rwlock::RwLockWriteGuard<'t17, raft::RaftMeta>, &'t18 mut utils::rwlock::RwLockWriteGuard<'t19, raft::RaftMeta>, impl core::future::future::Future, impl core::future::future::Future, (), (), i64, i64, bool, bool, i64, u64, std::time::Duration, tokio::time::delay::Delay, tokio::time::delay::Delay, (), ()}: std::marker::Send`
#3 [typeck_tables_of] processing `raft::RaftService::start`
#4 [typeck_tables_of] processing `raft::RaftService::start::{{closure}}#0`
#5 [type_of] processing `raft::RaftService::start::{{closure}}#0`
#6 [collect_mod_item_types] collecting item types in module `raft`
#7 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `bifrost`.

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

[Aaron1011]

Minimized (use rustc -C incremental=1 --edition=2018 to reproduce):

#![feature(const_generics)]

const FOO: usize = 1;

struct Container<T> {
    val: std::marker::PhantomData<T>,
    blah: [(); FOO]
}

async fn dummy() {}

async fn foo() {
    let a: Container<&'static ()>;
    dummy().await;
}

fn is_send<T: Send>(_: T) {}

fn main() {
    is_send(foo());
}

There's a lot going on here:

1. We compute the witness type for foo, erasing &'static to a new ReLateBound
2. We try to evaluate an auto-trait predicate for the opaque return value of foo. This requires us to evaluate Container<T>: Send, with the late-bound region type &_# () substituted in for T.
3. Evaluation succeeds, giving us an auto-impl candidate.
4. In SelectionContext::collect_predicates_for_types, we replace the late-bound region with a placeholder region, and try to normalize the auto-impl candidate.
5. During normalization, we try to const-eval [(); FOO] (a constituent type of Container)
6. Since #![feature(const_generics)] is enabled, we use the proper generic substs for the reference to FOO - namely, we provide T as a subst, since the unevaluated expression might use it.
7. Since T is the placeholder-instantiated type &_# (), we try to const-eval an Instance with a placeholder region in its substs.
8. Incremental compilation is enabled, so we ICE.

EDIT: I may be wrong about where exactly the placeholder region is getting created.

In the original ICE, the #![feature(const_generics)] came from liballoc, and the LeafNode struct takes the place of Container.

[Aaron1011]

This should be fixed by #67717, since canonicalized const-eval queries can handle placeholder regions.

[pnkfelix]

triage: P-high, removing nomination label. Assigning to @Aaron1011