Escaping bound vars in predicate with `associated_type_bounds`

[jackh726]

Code

#![feature(associated_type_bounds)]
trait TraitA<'a> { type AsA; }
trait TraitB<'a, 'b> { type AsB; }
trait TraitC<'a, 'b, 'c> {}
struct X;
impl<'a, 'b, 'c> TraitC<'a, 'b, 'c> for X {}
struct Y;
impl<'a, 'b> TraitB<'a, 'b> for Y { type AsB = X; }
struct Z;
impl<'a> TraitA<'a> for Z { type AsA = Y; }
fn foo<T>() where for<'a> T: TraitA<'a, AsA: for<'b> TraitB<'a, 'b, AsB: for<'c> TraitC<'a, 'b, 'c>>> {}
fn main() {
    foo::<Z>();
}

Meta

rustc 1.52.0-nightly (f98721f88 2021-03-10) running on x86_64-unknown-linux-gnu

Output

error: internal compiler error: compiler/rustc_typeck/src/check/inherited.rs:135:13: escaping bound vars in predicate Obligation(predicate=Binder(TraitPredicate(<<Z as TraitA<'a>>::AsA as TraitB<'a, 'b>>)), depth=0)
  --> src/main.rs:48:5
   |
48 |     foo::<Z>();
   |     ^^^^^^^^

Backtrace

thread 'rustc' panicked at 'Box<Any>', /rustc/f98721f886ab52d32d622ad0a46216ad03f3e525/library/std/src/panic.rs:59:5
stack backtrace:
   0: std::panicking::begin_panic
   1: std::panic::panic_any
   2: rustc_errors::HandlerInner::span_bug
   3: rustc_errors::Handler::span_bug
   4: rustc_middle::ty::context::tls::with_opt
   5: rustc_middle::util::bug::opt_span_bug_fmt
   6: rustc_middle::util::bug::span_bug_fmt
   7: rustc_typeck::check::inherited::Inherited::register_predicate
   8: rustc_typeck::check::fn_ctxt::_impl::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::add_required_obligations
   9: rustc_typeck::check::fn_ctxt::_impl::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::instantiate_value_path
  10: rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_kind
  11: rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation
  12: rustc_typeck::check::callee::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_call
  13: rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_kind
  14: rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation
  15: rustc_typeck::check::fn_ctxt::checks::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_stmt
  16: rustc_typeck::check::fn_ctxt::checks::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_block_with_expected
  17: rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation
  18: rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_return_expr
  19: rustc_typeck::check::check::check_fn
  20: rustc_infer::infer::InferCtxtBuilder::enter
  21: rustc_typeck::check::typeck
  22: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  23: rustc_data_structures::stack::ensure_sufficient_stack
  24: rustc_query_system::query::plumbing::force_query_with_job
  25: rustc_query_system::query::plumbing::get_query_impl
  26: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::typeck
  27: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::par_body_owners
  28: rustc_typeck::check::typeck_item_bodies
  29: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  30: rustc_data_structures::stack::ensure_sufficient_stack
  31: rustc_query_system::query::plumbing::force_query_with_job
  32: rustc_query_system::query::plumbing::get_query_impl
  33: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::typeck_item_bodies
  34: rustc_session::utils::<impl rustc_session::session::Session>::time
  35: rustc_typeck::check_crate
  36: rustc_interface::passes::analysis
  37: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  38: rustc_data_structures::stack::ensure_sufficient_stack
  39: rustc_query_system::query::plumbing::force_query_with_job
  40: rustc_query_system::query::plumbing::get_query_impl
  41: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  42: rustc_interface::passes::QueryContext::enter
  43: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  44: rustc_span::with_source_map
  45: rustc_interface::interface::create_compiler_and_run
  46: rustc_span::with_session_globals
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.52.0-nightly (f98721f88 2021-03-10) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

query stack during panic:
#0 [typeck] type-checking `main`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack

playground

[JohnTitor]

Triage: The ICE has been fixed in the latest nightly, I guess #84377 fixed it? Marking as E-needs-test.

[jackh726]

Oh wooh. Guess #84377 actually did fix things.