ICE: `unexpected type encountered in variance inference: _`

[matthiaskrgr]

Code

pub trait Iter {
    type Item<'a> where Self: 'a;

    fn next<'a>(&'a mut self) -> Option<Windows<T>>;

    fn for_each<F>(&'a mut self, mut f: F)
        where Self: Sized, F: for<'a> FnMut(Self::Windows<'a>)
    {
      todo!()
    }
}

pub struct Windows<T> {}

impl<T> Windows<'a> {
    type Item<'a> where T: 'a = &'a mut [T];

    fn next<'a>(&'a mut self) -> Option<Self::Item<'a>> {
        todo!();
    }
}

impl<T> Iter for Windows<T> {

    fn T<'a>(&'for_each mut self) -> Option<Self::Item<'a>> {
        todo!();
    }
}

Meta

rustc --version --verbose:

rustc 1.70.0-nightly (7b4f48927 2023-03-12)
binary: rustc
commit-hash: 7b4f48927dce585f747a58083b45ab62b9d73a53
commit-date: 2023-03-12
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 15.0.7

Error output

error[E0261]: use of undeclared lifetime name `'a`
 --> 48.rs:6:21
  |
6 |     fn for_each<F>(&'a mut self, mut f: F)
  |                     ^^ undeclared lifetime
  |
help: consider introducing lifetime `'a` here
  |
6 |     fn for_each<'a, F>(&'a mut self, mut f: F)
  |                 +++
help: consider introducing lifetime `'a` here
  |
1 | pub trait Iter<'a> {
  |               ++++

error[E0261]: use of undeclared lifetime name `'a`
  --> 48.rs:15:17
   |
15 | impl<T> Windows<'a> {
   |      -          ^^ undeclared lifetime
   |      |
   |      help: consider introducing lifetime `'a` here: `'a,`

error[E0407]: method `T` is not a member of trait `Iter`
  --> 48.rs:25:5
   |
25 | /     fn T<'a>(&'for_each mut self) -> Option<Self::Item<'a>> {
26 | |         todo!();
27 | |     }
   | |_____^ not a member of trait `Iter`

error[E0261]: use of undeclared lifetime name `'for_each`
  --> 48.rs:25:15
   |
25 |     fn T<'a>(&'for_each mut self) -> Option<Self::Item<'a>> {
   |               ^^^^^^^^^ undeclared lifetime
   |
help: consider introducing lifetime `'for_each` here
   |
25 |     fn T<'for_each, 'a>(&'for_each mut self) -> Option<Self::Item<'a>> {
   |          ++++++++++
help: consider introducing lifetime `'for_each` here
   |
23 | impl<'for_each, T> Iter for Windows<T> {
   |      ++++++++++

error[E0412]: cannot find type `T` in this scope
 --> 48.rs:4:49
  |
4 |     fn next<'a>(&'a mut self) -> Option<Windows<T>>;
  |                                                 ^ not found in this scope

warning: where clause not allowed here
  --> 48.rs:16:19
   |
16 |     type Item<'a> where T: 'a = &'a mut [T];
   |                   ^^^^^^^^^^^
   |
   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
   = note: `#[warn(deprecated_where_clause_location)]` on by default
help: move it to the end of the type declaration
   |
16 -     type Item<'a> where T: 'a = &'a mut [T];
16 +     type Item<'a>  = &'a mut [T] where T: 'a;
   |

error[E0601]: `main` function not found in crate `48`
  --> 48.rs:28:2
   |
28 | }
   |  ^ consider adding a `main` function to `48.rs`

error[E0107]: struct takes 0 lifetime arguments but 1 lifetime argument was supplied
  --> 48.rs:15:9
   |
15 | impl<T> Windows<'a> {
   |         ^^^^^^^---- help: remove these generics
   |         |
   |         expected 0 lifetime arguments
   |
note: struct defined here, with 0 lifetime parameters
  --> 48.rs:13:12
   |
13 | pub struct Windows<T> {}
   |            ^^^^^^^

error[E0107]: struct takes 1 generic argument but 0 generic arguments were supplied
  --> 48.rs:15:9
   |
15 | impl<T> Windows<'a> {
   |         ^^^^^^^ expected 1 generic argument
   |
note: struct defined here, with 1 generic parameter: `T`
  --> 48.rs:13:12
   |
13 | pub struct Windows<T> {}
   |            ^^^^^^^ -
help: add missing generic argument
   |
15 | impl<T> Windows<'a, T> {
   |                   +++

error[E0220]: associated type `Windows` not found for `Self`
 --> 48.rs:7:51
  |
7 |         where Self: Sized, F: for<'a> FnMut(Self::Windows<'a>)
  |                                                   ^^^^^^^ associated type `Windows` not found

error[E0658]: inherent associated types are unstable
  --> 48.rs:16:5
   |
16 |     type Item<'a> where T: 'a = &'a mut [T];
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #8995 <https://github.com/rust-lang/rust/issues/8995> for more information
   = help: add `#![feature(inherent_associated_types)]` to the crate attributes to enable

Backtrace

error: internal compiler error: compiler/rustc_hir_analysis/src/variance/constraints.rs:301:17: unexpected type encountered in variance inference: _

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/compiler/rustc_errors/src/lib.rs:1644:9
stack backtrace:
   0:     0x7f8c0716651a - std::backtrace_rs::backtrace::libunwind::trace::hf7d75cca16fd1b61
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f8c0716651a - std::backtrace_rs::backtrace::trace_unsynchronized::hf5ec95734aab509d
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f8c0716651a - std::sys_common::backtrace::_print_fmt::he95113413355c8cd
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f8c0716651a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h072d12f2e69ca92b
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f8c071c9c5e - core::fmt::write::h1d23f16415e96af2
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/core/src/fmt/mod.rs:1232:17
   5:     0x7f8c07159275 - std::io::Write::write_fmt::hcf1e413fde4ffcd5
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/io/mod.rs:1684:15
   6:     0x7f8c071662e5 - std::sys_common::backtrace::_print::h6b2b14bedd5177e7
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f8c071662e5 - std::sys_common::backtrace::print::h09ccebfbcd382e89
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f8c0716905f - std::panicking::default_hook::{{closure}}::h4ee055db778febc2
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/panicking.rs:271:22
   9:     0x7f8c07168d9b - std::panicking::default_hook::ha74f60e3a15d95fb
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/panicking.rs:290:9
  10:     0x7f8c0a497085 - rustc_driver_impl[d355a67661263e47]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f8c0716989d - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h7f34603beb945e8f
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/alloc/src/boxed.rs:2002:9
  12:     0x7f8c0716989d - std::panicking::rust_panic_with_hook::h4b5d379936d4932f
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/panicking.rs:696:13
  13:     0x7f8c0aa02371 - std[e52d7c968ed01318]::panicking::begin_panic::<rustc_errors[45159b7f7e36021d]::ExplicitBug>::{closure#0}
  14:     0x7f8c0a9fdaa6 - std[e52d7c968ed01318]::sys_common::backtrace::__rust_end_short_backtrace::<std[e52d7c968ed01318]::panicking::begin_panic<rustc_errors[45159b7f7e36021d]::ExplicitBug>::{closure#0}, !>
  15:     0x7f8c0aa86046 - std[e52d7c968ed01318]::panicking::begin_panic::<rustc_errors[45159b7f7e36021d]::ExplicitBug>
  16:     0x7f8c0aa51e06 - std[e52d7c968ed01318]::panic::panic_any::<rustc_errors[45159b7f7e36021d]::ExplicitBug>
  17:     0x7f8c0aa4d966 - <rustc_errors[45159b7f7e36021d]::HandlerInner>::bug::<&alloc[fc860cae0dfa1ab1]::string::String>
  18:     0x7f8c0aa4d630 - <rustc_errors[45159b7f7e36021d]::Handler>::bug::<&alloc[fc860cae0dfa1ab1]::string::String>
  19:     0x7f8c0aa39a9b - rustc_middle[a96ac5d591578447]::util::bug::opt_span_bug_fmt::<rustc_span[f8bdfaef83e46314]::span_encoding::Span>::{closure#0}
  20:     0x7f8c0aa384fa - rustc_middle[a96ac5d591578447]::ty::context::tls::with_opt::<rustc_middle[a96ac5d591578447]::util::bug::opt_span_bug_fmt<rustc_span[f8bdfaef83e46314]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7f8c0aa384c6 - rustc_middle[a96ac5d591578447]::ty::context::tls::with_context_opt::<rustc_middle[a96ac5d591578447]::ty::context::tls::with_opt<rustc_middle[a96ac5d591578447]::util::bug::opt_span_bug_fmt<rustc_span[f8bdfaef83e46314]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7f8c0aa399e6 - rustc_middle[a96ac5d591578447]::util::bug::opt_span_bug_fmt::<rustc_span[f8bdfaef83e46314]::span_encoding::Span>
  23:     0x7f8c08ab44b3 - rustc_middle[a96ac5d591578447]::util::bug::bug_fmt
  24:     0x7f8c08c3e6bd - <rustc_hir_analysis[357075c2c3fc2a7b]::variance::constraints::ConstraintContext>::add_constraints_from_ty
  25:     0x7f8c08c3dc69 - <rustc_hir_analysis[357075c2c3fc2a7b]::variance::constraints::ConstraintContext>::add_constraints_from_ty
  26:     0x7f8c08c3d247 - <rustc_hir_analysis[357075c2c3fc2a7b]::variance::constraints::ConstraintContext>::build_constraints_for_item
  27:     0x7f8c08c3cc9a - rustc_hir_analysis[357075c2c3fc2a7b]::variance::constraints::add_constraints_from_crate
  28:     0x7f8c08c3c123 - rustc_hir_analysis[357075c2c3fc2a7b]::variance::crate_variances
  29:     0x7f8c09cbe53b - rustc_query_system[704b80a7bc44cd49]::query::plumbing::try_execute_query::<rustc_query_impl[217bee59c5548bf5]::queries::crate_variances, rustc_query_impl[217bee59c5548bf5]::plumbing::QueryCtxt>
  30:     0x7f8c09cbe210 - <rustc_query_impl[217bee59c5548bf5]::Queries as rustc_middle[a96ac5d591578447]::ty::query::QueryEngine>::crate_variances
  31:     0x7f8c0945afcc - rustc_hir_analysis[357075c2c3fc2a7b]::variance::variances_of
  32:     0x7f8c09458cc8 - rustc_query_system[704b80a7bc44cd49]::query::plumbing::try_execute_query::<rustc_query_impl[217bee59c5548bf5]::queries::variances_of, rustc_query_impl[217bee59c5548bf5]::plumbing::QueryCtxt>
  33:     0x7f8c094588bd - <rustc_query_impl[217bee59c5548bf5]::Queries as rustc_middle[a96ac5d591578447]::ty::query::QueryEngine>::variances_of
  34:     0x7f8c0850e26c - rustc_middle[a96ac5d591578447]::ty::relate::super_relate_tys::<rustc_infer[8071ebb96624e335]::infer::sub::Sub>
  35:     0x7f8c0850a261 - <rustc_infer[8071ebb96624e335]::infer::sub::Sub as rustc_middle[a96ac5d591578447]::ty::relate::TypeRelation>::tys
  36:     0x7f8c099e52a3 - <rustc_infer[8071ebb96624e335]::infer::InferCtxt>::commit_if_ok::<rustc_infer[8071ebb96624e335]::infer::InferOk<()>, rustc_middle[a96ac5d591578447]::ty::error::TypeError, <rustc_infer[8071ebb96624e335]::infer::at::Trace>::sub<rustc_middle[a96ac5d591578447]::ty::Ty>::{closure#0}>
  37:     0x7f8c099e50d7 - <rustc_trait_selection[8ee7c2d509810bbf]::traits::engine::ObligationCtxt>::sup::<rustc_middle[a96ac5d591578447]::ty::Ty>
  38:     0x7f8c0a5c340a - <rustc_infer[8071ebb96624e335]::infer::InferCtxt>::probe::<core[125d846441ac421f]::option::Option<(rustc_span[f8bdfaef83e46314]::def_id::DefId, rustc_span[f8bdfaef83e46314]::def_id::DefId, &rustc_middle[a96ac5d591578447]::ty::list::List<rustc_middle[a96ac5d591578447]::ty::subst::GenericArg>)>, <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::lookup_inherent_assoc_ty::{closure#1}::{closure#0}>
  39:     0x7f8c0a5bfba6 - <&mut <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::lookup_inherent_assoc_ty::{closure#1} as core[125d846441ac421f]::ops::function::FnMut<(&(rustc_span[f8bdfaef83e46314]::def_id::DefId, (rustc_span[f8bdfaef83e46314]::def_id::DefId, rustc_span[f8bdfaef83e46314]::def_id::DefId)),)>>::call_mut
  40:     0x7f8c0a605bee - <alloc[fc860cae0dfa1ab1]::vec::Vec<(rustc_span[f8bdfaef83e46314]::def_id::DefId, rustc_span[f8bdfaef83e46314]::def_id::DefId, &rustc_middle[a96ac5d591578447]::ty::list::List<rustc_middle[a96ac5d591578447]::ty::subst::GenericArg>)> as alloc[fc860cae0dfa1ab1]::vec::spec_from_iter::SpecFromIter<(rustc_span[f8bdfaef83e46314]::def_id::DefId, rustc_span[f8bdfaef83e46314]::def_id::DefId, &rustc_middle[a96ac5d591578447]::ty::list::List<rustc_middle[a96ac5d591578447]::ty::subst::GenericArg>), core[125d846441ac421f]::iter::adapters::filter_map::FilterMap<core[125d846441ac421f]::slice::iter::Iter<(rustc_span[f8bdfaef83e46314]::def_id::DefId, (rustc_span[f8bdfaef83e46314]::def_id::DefId, rustc_span[f8bdfaef83e46314]::def_id::DefId))>, <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::lookup_inherent_assoc_ty::{closure#1}>>>::from_iter
  41:     0x7f8c09312a66 - <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::associated_path_to_ty::{closure#0}
  42:     0x7f8c092f75a6 - <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  43:     0x7f8c092fb21c - <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::res_to_ty
  44:     0x7f8c092f725e - <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  45:     0x7f8c09390a3b - <dyn rustc_hir_analysis[357075c2c3fc2a7b]::astconv::AstConv>::ty_of_fn::{closure#0}
  46:     0x7f8c09402d35 - rustc_hir_analysis[357075c2c3fc2a7b]::collect::fn_sig
  47:     0x7f8c09401140 - rustc_query_system[704b80a7bc44cd49]::query::plumbing::try_execute_query::<rustc_query_impl[217bee59c5548bf5]::queries::fn_sig, rustc_query_impl[217bee59c5548bf5]::plumbing::QueryCtxt>
  48:     0x7f8c08c805a1 - <rustc_hir_analysis[357075c2c3fc2a7b]::collect::CollectItemTypesVisitor as rustc_hir[4aa57babd8685147]::intravisit::Visitor>::visit_impl_item
  49:     0x7f8c08c7aa41 - <rustc_middle[a96ac5d591578447]::hir::map::Map>::visit_item_likes_in_module::<rustc_hir_analysis[357075c2c3fc2a7b]::collect::CollectItemTypesVisitor>
  50:     0x7f8c08c7a84c - rustc_hir_analysis[357075c2c3fc2a7b]::collect::collect_mod_item_types
  51:     0x7f8c09ac706e - rustc_query_system[704b80a7bc44cd49]::query::plumbing::try_execute_query::<rustc_query_impl[217bee59c5548bf5]::queries::collect_mod_item_types, rustc_query_impl[217bee59c5548bf5]::plumbing::QueryCtxt>
  52:     0x7f8c09ac6bf3 - <rustc_query_impl[217bee59c5548bf5]::Queries as rustc_middle[a96ac5d591578447]::ty::query::QueryEngine>::collect_mod_item_types
  53:     0x7f8c087b0363 - <rustc_session[7e23441c2db8ce4a]::session::Session>::track_errors::<rustc_hir_analysis[357075c2c3fc2a7b]::check_crate::{closure#0}, ()>
  54:     0x7f8c087acce2 - rustc_hir_analysis[357075c2c3fc2a7b]::check_crate
  55:     0x7f8c087a2d12 - rustc_interface[6bf42eb308c32713]::passes::analysis
  56:     0x7f8c09cab71c - rustc_query_system[704b80a7bc44cd49]::query::plumbing::try_execute_query::<rustc_query_impl[217bee59c5548bf5]::queries::analysis, rustc_query_impl[217bee59c5548bf5]::plumbing::QueryCtxt>
  57:     0x7f8c09cab410 - <rustc_query_impl[217bee59c5548bf5]::Queries as rustc_middle[a96ac5d591578447]::ty::query::QueryEngine>::analysis
  58:     0x7f8c09ad02f9 - <rustc_middle[a96ac5d591578447]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[d355a67661263e47]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>>
  59:     0x7f8c096c8498 - rustc_span[f8bdfaef83e46314]::with_source_map::<core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>, rustc_interface[6bf42eb308c32713]::interface::run_compiler<core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>, rustc_driver_impl[d355a67661263e47]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  60:     0x7f8c096bf70c - std[e52d7c968ed01318]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[6bf42eb308c32713]::util::run_in_thread_pool_with_globals<rustc_interface[6bf42eb308c32713]::interface::run_compiler<core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>, rustc_driver_impl[d355a67661263e47]::run_compiler::{closure#1}>::{closure#0}, core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>>
  61:     0x7f8c096bf13a - <<std[e52d7c968ed01318]::thread::Builder>::spawn_unchecked_<rustc_interface[6bf42eb308c32713]::util::run_in_thread_pool_with_globals<rustc_interface[6bf42eb308c32713]::interface::run_compiler<core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>, rustc_driver_impl[d355a67661263e47]::run_compiler::{closure#1}>::{closure#0}, core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[125d846441ac421f]::result::Result<(), rustc_span[f8bdfaef83e46314]::ErrorGuaranteed>>::{closure#1} as core[125d846441ac421f]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  62:     0x7f8c07173793 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hc0a50816e1eb2bba
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/alloc/src/boxed.rs:1988:9
  63:     0x7f8c07173793 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb2f83fc2049033c3
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/alloc/src/boxed.rs:1988:9
  64:     0x7f8c07173793 - std::sys::unix::thread::Thread::new::thread_start::hce5861512f8bf7ea
                               at /rustc/7b4f48927dce585f747a58083b45ab62b9d73a53/library/std/src/sys/unix/thread.rs:108:17
  65:     0x7f8c06f05bb5 - <unknown>
  66:     0x7f8c06f87d90 - <unknown>
  67:                0x0 - <unknown>

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 1.70.0-nightly (7b4f48927 2023-03-12) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [crate_variances] computing the variances for items in this crate
#1 [variances_of] computing the variances of `Windows`
#2 [fn_sig] computing function signature of `<impl at 48.rs:23:1: 23:28>::T`
#3 [collect_mod_item_types] collecting item types in top-level module
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 11 previous errors; 1 warning emitted

Some errors have detailed explanations: E0107, E0220, E0261, E0407, E0412, E0601, E0658.
For more information about an error, try `rustc --explain E0107`.

[langston-barrett]

Minimized with treereduce:

struct Windows<T> {}

impl<T> Windows {
    type Item = &[T];

    fn next() -> Option<Self::Item> {}
}

impl<T> Windows<T> {
    fn T() -> Option<Self::Item> {}
}

@rustbot label +S-bug-has-mcve

[matthiaskrgr]

searched toolchains 7aa413d through 5243ea5

---

Regression in 7b55296

---

[bwmf2]

Alternative:

#![allow(incomplete_features)]
#![feature(inherent_associated_types)]

struct Windows<T> {}

impl<T> Windows<()> {
    type Item = T;

    fn next() -> Self::Item {}
}

impl<T> Windows<T> {
    fn gates() -> Self::Item {}
}

Would the error change if the compiler is built with debug = true?

[JohnTitor]

Triage: This is no longer ICE since today's nightly, I assume #109410 fixed it. Marking as E-needs-test just in case regression tests there didn't cover this case.
@rustbot labels: +E-needs-test