Escaping late-bound regions during canonicalization with associated type bounds

[jackh726]

Code

#![feature(associated_type_bounds)]
trait A<'a, 'b> {}
trait B<'a, 'b, 'c> {}
fn err<'u, 'a, F>() where for<'b> F: Iterator<Item: for<'c> B<'a, 'b, 'c> + for<'c> A<'a, 'c>> {}

Meta

rustc 1.51.0-nightly (d98d2f57d 2021-01-18)

Error output

error: internal compiler error: compiler/rustc_infer/src/infer/canonical/canonicalizer.rs:310:21: escaping late-bound region during canonicalization

Backtrace

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::bug
   2: rustc_errors::Handler::bug
   3: rustc_middle::ty::context::tls::with_opt
   4: rustc_middle::util::bug::opt_span_bug_fmt
   5: rustc_middle::util::bug::bug_fmt
   6: <rustc_infer::infer::canonical::canonicalizer::Canonicalizer as rustc_middle::ty::fold::TypeFolder>::fold_region
   7: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend
   8: rustc_middle::ty::fold::TypeFoldable::fold_with
   9: rustc_middle::ty::fold::TypeFoldable::fold_with
  10: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend
  11: rustc_middle::ty::util::fold_list
  12: rustc_infer::infer::canonical::canonicalizer::Canonicalizer::canonicalize
  13: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::outlives_bounds::InferCtxtExt>::implied_outlives_bounds
  14: <rustc_infer::infer::outlives::env::OutlivesEnvironment as rustc_trait_selection::infer::OutlivesEnvironmentExt>::add_implied_bounds
  15: rustc_typeck::check::regionck::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::regionck_item
  16: rustc_infer::infer::InferCtxtBuilder::enter
  17: rustc_typeck::check::wfcheck::check_item_well_formed
  18: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_item_well_formed>::compute
  19: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  20: rustc_data_structures::stack::ensure_sufficient_stack
  21: rustc_query_system::query::plumbing::force_query_with_job
  22: rustc_query_system::query::plumbing::get_query_impl
  23: rustc_query_system::query::plumbing::ensure_query_impl
  24: <rustc_typeck::check::wfcheck::CheckTypeWellFormedVisitor as rustc_hir::itemlikevisit::ParItemLikeVisitor>::visit_item
  25: rustc_data_structures::sync::par_for_each_in
  26: rustc_hir::hir::Crate::par_visit_all_item_likes
  27: rustc_typeck::check_crate
  28: rustc_interface::passes::analysis
  29: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  30: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  31: rustc_data_structures::stack::ensure_sufficient_stack
  32: rustc_query_system::query::plumbing::force_query_with_job
  33: rustc_query_system::query::plumbing::get_query_impl
  34: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  35: rustc_span::with_source_map
  36: rustc_interface::interface::create_compiler_and_run
  37: 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 1.51.0-nightly (d98d2f57d 2021-01-18) 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 [check_item_well_formed] checking that `err` is well-formed
#1 [analysis] running analysis passes on this crate
end of query stack

Playground link: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=1ac61e265f265fb1a096491da37893ff

[jackh726]

@rustbot label: +requires-nightly +F-associated_type_bounds

[JohnTitor]

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