ICE: unexpected borrowck region with `type_alias_impl_trait` with lifetime

[SparkyPotato]

Code

#![feature(type_alias_impl_trait)]

struct call_me;

type ReturnType<'a> = impl std::future::Future<Output = u32> + 'a;
type FnType = impl Fn(&u32) -> ReturnType;

impl std::ops::Deref for call_me {
    type Target = FnType;
    
    fn deref(&self) -> &Self::Target {
        fn inner(val: &u32) -> ReturnType {
            async move {
                *val * 2
            }
        }
    
        &inner
    }
}

Explicitly giving lifetimes to FnType with for<'a> FnOnce(&'a u32) -> ReturnType<'a> and doing the same on inner does not fix the ICE either.

Meta

Version rustc 1.70.0-nightly (8a73f50d8 2023-03-11)

Error output

error: internal compiler error: compiler/rustc_middle/src/ty/opaque_types.rs:121:17: unexpected region kind in opaque type: RePlaceholder(Placeholder { universe: U3, name: BrNamed(DefId(0:15 ~ playground[419e]::FnType::{opaque#0}::'_), '_) })

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/compiler/rustc_errors/src/lib.rs:1644:9
stack backtrace:
   0:     0x7f461097651a - std::backtrace_rs::backtrace::libunwind::trace::h8e11308176f74878
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f461097651a - std::backtrace_rs::backtrace::trace_unsynchronized::h08cc8e766dddc25f
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f461097651a - std::sys_common::backtrace::_print_fmt::h99c527e41798f0e9
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f461097651a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h79914c19e70ec78b
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f46109d9c5e - core::fmt::write::h667853c5e38f13ec
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/core/src/fmt/mod.rs:1232:17
   5:     0x7f4610969275 - std::io::Write::write_fmt::hba0992fb471f923a
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/io/mod.rs:1684:15
   6:     0x7f46109762e5 - std::sys_common::backtrace::_print::h215545a75453f830
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f46109762e5 - std::sys_common::backtrace::print::hff9ee2dce3d2dcea
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f461097905f - std::panicking::default_hook::{{closure}}::h8fb87de14fa60e54
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/panicking.rs:271:22
   9:     0x7f4610978d9b - std::panicking::default_hook::h319d8219a84d729a
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/panicking.rs:290:9
  10:     0x7f4613c990d5 - <rustc_driver_impl[de28347a8abf8356]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[d9ef29759c2251a8]::ops::function::FnOnce<(&core[d9ef29759c2251a8]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f461097989d - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hf7dd68431c765c20
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/alloc/src/boxed.rs:2002:9
  12:     0x7f461097989d - std::panicking::rust_panic_with_hook::h65b020dd76c4cd89
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/panicking.rs:696:13
  13:     0x7f4614204031 - std[bc2958bd9c820bb9]::panicking::begin_panic::<rustc_errors[24bb4dbb092f22f2]::ExplicitBug>::{closure#0}
  14:     0x7f46141ff766 - std[bc2958bd9c820bb9]::sys_common::backtrace::__rust_end_short_backtrace::<std[bc2958bd9c820bb9]::panicking::begin_panic<rustc_errors[24bb4dbb092f22f2]::ExplicitBug>::{closure#0}, !>
  15:     0x7f4614286ae6 - std[bc2958bd9c820bb9]::panicking::begin_panic::<rustc_errors[24bb4dbb092f22f2]::ExplicitBug>
  16:     0x7f4614252bd6 - std[bc2958bd9c820bb9]::panic::panic_any::<rustc_errors[24bb4dbb092f22f2]::ExplicitBug>
  17:     0x7f461424f456 - <rustc_errors[24bb4dbb092f22f2]::HandlerInner>::bug::<&alloc[66b6468aa09e7a1]::string::String>
  18:     0x7f461424f120 - <rustc_errors[24bb4dbb092f22f2]::Handler>::bug::<&alloc[66b6468aa09e7a1]::string::String>
  19:     0x7f461423b58b - rustc_middle[c2bebf1196c36ca]::util::bug::opt_span_bug_fmt::<rustc_span[67f48ae15a2a1ace]::span_encoding::Span>::{closure#0}
  20:     0x7f4614239fea - rustc_middle[c2bebf1196c36ca]::ty::context::tls::with_opt::<rustc_middle[c2bebf1196c36ca]::util::bug::opt_span_bug_fmt<rustc_span[67f48ae15a2a1ace]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7f4614239fb6 - rustc_middle[c2bebf1196c36ca]::ty::context::tls::with_context_opt::<rustc_middle[c2bebf1196c36ca]::ty::context::tls::with_opt<rustc_middle[c2bebf1196c36ca]::util::bug::opt_span_bug_fmt<rustc_span[67f48ae15a2a1ace]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7f461423b4d6 - rustc_middle[c2bebf1196c36ca]::util::bug::opt_span_bug_fmt::<rustc_span[67f48ae15a2a1ace]::span_encoding::Span>
  23:     0x7f4612243563 - rustc_middle[c2bebf1196c36ca]::util::bug::bug_fmt
  24:     0x7f4613287af6 - <rustc_middle[c2bebf1196c36ca]::ty::opaque_types::ReverseMapper as rustc_type_ir[99c45160e9dcd5d5]::fold::TypeFolder<rustc_middle[c2bebf1196c36ca]::ty::context::TyCtxt>>::fold_region
  25:     0x7f46131d26ff - <&rustc_middle[c2bebf1196c36ca]::ty::list::List<rustc_middle[c2bebf1196c36ca]::ty::subst::GenericArg> as rustc_type_ir[99c45160e9dcd5d5]::fold::TypeFoldable<rustc_middle[c2bebf1196c36ca]::ty::context::TyCtxt>>::try_fold_with::<rustc_middle[c2bebf1196c36ca]::ty::opaque_types::ReverseMapper>
  26:     0x7f46131d2359 - <rustc_middle[c2bebf1196c36ca]::ty::Ty as rustc_type_ir[99c45160e9dcd5d5]::fold::TypeSuperFoldable<rustc_middle[c2bebf1196c36ca]::ty::context::TyCtxt>>::super_fold_with::<rustc_middle[c2bebf1196c36ca]::ty::opaque_types::ReverseMapper>
  27:     0x7f46134a2d2c - <rustc_infer[d6af38f28f637c8d]::infer::InferCtxt as rustc_borrowck[b0ecc8244f8d9953]::region_infer::opaque_types::InferCtxtExt>::infer_opaque_definition_from_instantiation
  28:     0x7f4612689f8a - <rustc_borrowck[b0ecc8244f8d9953]::region_infer::RegionInferenceContext>::infer_opaque_types
  29:     0x7f4612682dba - rustc_borrowck[b0ecc8244f8d9953]::nll::compute_regions
  30:     0x7f4612652473 - rustc_borrowck[b0ecc8244f8d9953]::do_mir_borrowck
  31:     0x7f461264fb11 - <rustc_borrowck[b0ecc8244f8d9953]::provide::{closure#0} as core[d9ef29759c2251a8]::ops::function::FnOnce<(rustc_middle[c2bebf1196c36ca]::ty::context::TyCtxt, rustc_span[67f48ae15a2a1ace]::def_id::LocalDefId)>>::call_once
  32:     0x7f461264dc5d - rustc_query_system[bb54613dbf60299b]::query::plumbing::try_execute_query::<rustc_query_impl[6873813250a98cc1]::queries::mir_borrowck, rustc_query_impl[6873813250a98cc1]::plumbing::QueryCtxt>
  33:     0x7f461264d90a - <rustc_query_impl[6873813250a98cc1]::Queries as rustc_middle[c2bebf1196c36ca]::ty::query::QueryEngine>::mir_borrowck
  34:     0x7f4613e1d2c9 - <rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>::check
  35:     0x7f4613e1a7b2 - <rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator as rustc_hir[3dffec1ee7877645]::intravisit::Visitor>::visit_nested_impl_item
  36:     0x7f4613df5bb6 - rustc_hir[3dffec1ee7877645]::intravisit::walk_item::<rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>
  37:     0x7f4613e1a6dd - <rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator as rustc_hir[3dffec1ee7877645]::intravisit::Visitor>::visit_nested_item
  38:     0x7f4613df3d78 - rustc_hir[3dffec1ee7877645]::intravisit::walk_mod::<rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::find_opaque_ty_constraints_for_tait::ConstraintLocator>
  39:     0x7f4613e1ca21 - rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::find_opaque_ty_constraints_for_tait
  40:     0x7f461318ada6 - rustc_hir_analysis[d31dbb230cf00630]::collect::type_of::type_of
  41:     0x7f461259ef80 - rustc_query_system[bb54613dbf60299b]::query::plumbing::try_execute_query::<rustc_query_impl[6873813250a98cc1]::queries::type_of, rustc_query_impl[6873813250a98cc1]::plumbing::QueryCtxt>
  42:     0x7f461259d90c - <rustc_query_impl[6873813250a98cc1]::Queries as rustc_middle[c2bebf1196c36ca]::ty::query::QueryEngine>::type_of
  43:     0x7f46127fb145 - rustc_hir_analysis[d31dbb230cf00630]::check::check::check_mod_item_types
  44:     0x7f46132c7ec5 - rustc_query_system[bb54613dbf60299b]::query::plumbing::try_execute_query::<rustc_query_impl[6873813250a98cc1]::queries::check_mod_item_types, rustc_query_impl[6873813250a98cc1]::plumbing::QueryCtxt>
  45:     0x7f46132c7a4a - <rustc_query_impl[6873813250a98cc1]::Queries as rustc_middle[c2bebf1196c36ca]::ty::query::QueryEngine>::check_mod_item_types
  46:     0x7f461202881d - <rustc_middle[c2bebf1196c36ca]::hir::map::Map>::for_each_module::<rustc_hir_analysis[d31dbb230cf00630]::check_crate::{closure#6}::{closure#0}>
  47:     0x7f4612025d98 - rustc_hir_analysis[d31dbb230cf00630]::check_crate
  48:     0x7f461201bcf2 - rustc_interface[50a97a4d78cc75fe]::passes::analysis
  49:     0x7f46134a6f7d - rustc_query_system[bb54613dbf60299b]::query::plumbing::try_execute_query::<rustc_query_impl[6873813250a98cc1]::queries::analysis, rustc_query_impl[6873813250a98cc1]::plumbing::QueryCtxt>
  50:     0x7f46134a6c7f - <rustc_query_impl[6873813250a98cc1]::Queries as rustc_middle[c2bebf1196c36ca]::ty::query::QueryEngine>::analysis
  51:     0x7f46132bc7b6 - <rustc_middle[c2bebf1196c36ca]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[de28347a8abf8356]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>>
  52:     0x7f4612ec9a28 - rustc_span[67f48ae15a2a1ace]::with_source_map::<core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>, rustc_interface[50a97a4d78cc75fe]::interface::run_compiler<core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>, rustc_driver_impl[de28347a8abf8356]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  53:     0x7f4612ec0bac - std[bc2958bd9c820bb9]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[50a97a4d78cc75fe]::util::run_in_thread_pool_with_globals<rustc_interface[50a97a4d78cc75fe]::interface::run_compiler<core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>, rustc_driver_impl[de28347a8abf8356]::run_compiler::{closure#1}>::{closure#0}, core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>>
  54:     0x7f4612ec05da - <<std[bc2958bd9c820bb9]::thread::Builder>::spawn_unchecked_<rustc_interface[50a97a4d78cc75fe]::util::run_in_thread_pool_with_globals<rustc_interface[50a97a4d78cc75fe]::interface::run_compiler<core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>, rustc_driver_impl[de28347a8abf8356]::run_compiler::{closure#1}>::{closure#0}, core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[d9ef29759c2251a8]::result::Result<(), rustc_span[67f48ae15a2a1ace]::ErrorGuaranteed>>::{closure#1} as core[d9ef29759c2251a8]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  55:     0x7f4610983793 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h2be05930b084af35
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/alloc/src/boxed.rs:1988:9
  56:     0x7f4610983793 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h2e27f2bce1de28fe
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/alloc/src/boxed.rs:1988:9
  57:     0x7f4610983793 - std::sys::unix::thread::Thread::new::thread_start::hce13d4cabe284bf1
                               at /rustc/8a73f50d875840b8077b8ec080fa41881d7ce40d/library/std/src/sys/unix/thread.rs:108:17
  58:     0x7f4610848609 - start_thread
  59:     0x7f461076b133 - clone
  60:                0x0 - <unknown>

[langston-barrett]

@rustbot label +S-bug-has-mcve

[JohnTitor]

Triage: Fixed on the latest nightly, @rustbot labels: +E-needs-test