[ICE]: `var types encountered in structurally_relate_consts: ?1c ?1c`

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.yqoNYHxs2mJh/rustc_testrunner_tmpdir_reporting.QC5ogv3zZwCi/mvce.rs:1:12
  |
1 | #![feature(generic_const_exprs)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
  = note: `#[warn(incomplete_features)]` on by default


thread 'rustc' (2051033) panicked at /rustc-dev/42d7d5292025a31aaf02100ae5bd664aca66bbbb/compiler/rustc_type_ir/src/relate.rs:582:13:
var types encountered in structurally_relate_consts: ?1c ?1c
stack backtrace:
   0:     0x7f9bf84dc009 - <<std[f97f41f4b941f83d]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[d89867bba8befc45]::fmt::Display>::fmt
   1:     0x7f9bf8c0ec1e - core[d89867bba8befc45]::fmt::write
   2:     0x7f9bf84f2436 - <std[f97f41f4b941f83d]::sys::stdio::unix::Stderr as std[f97f41f4b941f83d]::io::Write>::write_fmt
   3:     0x7f9bf84b12fe - std[f97f41f4b941f83d]::panicking::default_hook::{closure#0}
   4:     0x7f9bf84cecf3 - std[f97f41f4b941f83d]::panicking::default_hook
   5:     0x7f9bf72a978c - std[f97f41f4b941f83d]::panicking::update_hook::<alloc[4ab400356fefd9c6]::boxed::Box<rustc_driver_impl[94c2fdbf68adad86]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f9bf84cefd2 - std[f97f41f4b941f83d]::panicking::panic_with_hook
   7:     0x7f9bf84b13c2 - std[f97f41f4b941f83d]::panicking::panic_handler::{closure#0}
   8:     0x7f9bf84a80c9 - std[f97f41f4b941f83d]::sys::backtrace::__rust_end_short_backtrace::<std[f97f41f4b941f83d]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f9bf84b2e2d - __rustc[f60fb9840241c8c6]::rust_begin_unwind
  10:     0x7f9bf4f1f28c - core[d89867bba8befc45]::panicking::panic_fmt
  11:     0x7f9bfa86a2d2 - rustc_type_ir[e57b036b72c98f5]::relate::structurally_relate_consts::<rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt, rustc_type_ir[e57b036b72c98f5]::relate::solver_relating::SolverRelating<rustc_infer[222dbbcac456ce28]::infer::InferCtxt, rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt>>.cold
  12:     0x7f9bf9370882 - rustc_type_ir[e57b036b72c98f5]::relate::combine::super_combine_consts::<rustc_infer[222dbbcac456ce28]::infer::InferCtxt, rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt, rustc_type_ir[e57b036b72c98f5]::relate::solver_relating::SolverRelating<rustc_infer[222dbbcac456ce28]::infer::InferCtxt, rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt>>
  13:     0x7f9bf936d3f9 - rustc_next_trait_solver[cdf54091203d2f39]::canonical::unify_query_var_values::<rustc_trait_selection[a78496944b282a58]::solve::delegate::SolverDelegate, rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt>
  14:     0x7f9bf9e7e500 - rustc_next_trait_solver[cdf54091203d2f39]::canonical::instantiate_canonical_state::<rustc_trait_selection[a78496944b282a58]::solve::delegate::SolverDelegate, rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt, ()>
  15:     0x7f9bf9e7f018 - <rustc_trait_selection[a78496944b282a58]::solve::inspect::analyse::InspectCandidate>::instantiate_nested_goals
  16:     0x7f9bf9e83270 - <rustc_trait_selection[a78496944b282a58]::solve::fulfill::derive_errors::BestObligation as rustc_trait_selection[a78496944b282a58]::solve::inspect::analyse::ProofTreeVisitor>::visit_goal
  17:     0x7f9bf9e82ef4 - <rustc_infer[222dbbcac456ce28]::infer::InferCtxt as rustc_trait_selection[a78496944b282a58]::solve::inspect::analyse::InferCtxtProofTreeExt>::visit_proof_tree_at_depth::<rustc_trait_selection[a78496944b282a58]::solve::fulfill::derive_errors::BestObligation>
  18:     0x7f9bf97ba738 - rustc_trait_selection[a78496944b282a58]::solve::fulfill::derive_errors::find_best_leaf_obligation
  19:     0x7f9bf97ba0ec - <rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError as rustc_infer[222dbbcac456ce28]::traits::engine::FromSolverError<rustc_trait_selection[a78496944b282a58]::solve::fulfill::NextSolverError>>::from_solver_error
  20:     0x7f9bf972ce82 - <core[d89867bba8befc45]::iter::adapters::map::Map<core[d89867bba8befc45]::iter::adapters::chain::Chain<core[d89867bba8befc45]::iter::adapters::map::Map<thin_vec[e9bb81cf893152c1]::Drain<(rustc_infer[222dbbcac456ce28]::traits::Obligation<rustc_middle[7183fb41e9311d8f]::ty::predicate::Predicate>, core[d89867bba8befc45]::option::Option<rustc_next_trait_solver[cdf54091203d2f39]::solve::GoalStalledOn<rustc_middle[7183fb41e9311d8f]::ty::context::TyCtxt>>)>, <rustc_trait_selection[a78496944b282a58]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError> as rustc_infer[222dbbcac456ce28]::traits::engine::TraitEngine<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError>>::collect_remaining_errors::{closure#0}>, core[d89867bba8befc45]::iter::adapters::map::Map<alloc[4ab400356fefd9c6]::vec::drain::Drain<rustc_infer[222dbbcac456ce28]::traits::Obligation<rustc_middle[7183fb41e9311d8f]::ty::predicate::Predicate>>, <rustc_trait_selection[a78496944b282a58]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError> as rustc_infer[222dbbcac456ce28]::traits::engine::TraitEngine<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError>>::collect_remaining_errors::{closure#1}>>, <rustc_trait_selection[a78496944b282a58]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError> as rustc_infer[222dbbcac456ce28]::traits::engine::TraitEngine<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError>>::collect_remaining_errors::{closure#2}> as core[d89867bba8befc45]::iter::traits::iterator::Iterator>::next
  21:     0x7f9bf972cc99 - <rustc_trait_selection[a78496944b282a58]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError> as rustc_infer[222dbbcac456ce28]::traits::engine::TraitEngine<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError>>::collect_remaining_errors
  22:     0x7f9bf968c879 - <rustc_trait_selection[a78496944b282a58]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError> as rustc_infer[222dbbcac456ce28]::traits::engine::TraitEngine<rustc_trait_selection[a78496944b282a58]::traits::FulfillmentError>>::evaluate_obligations_error_on_ambiguity
  23:     0x7f9bf967d88a - rustc_trait_selection[a78496944b282a58]::traits::coherence::overlap
  24:     0x7f9bf4cdb407 - <rustc_middle[7183fb41e9311d8f]::traits::specialization_graph::Children as rustc_trait_selection[a78496944b282a58]::traits::specialize::specialization_graph::ChildrenExt>::insert
  25:     0x7f9bf8c80ef7 - <rustc_middle[7183fb41e9311d8f]::traits::specialization_graph::Graph as rustc_trait_selection[a78496944b282a58]::traits::specialize::specialization_graph::GraphExt>::insert
  26:     0x7f9bf8c822db - rustc_trait_selection[a78496944b282a58]::traits::specialize::specialization_graph_provider
  27:     0x7f9bf8f25c77 - rustc_query_impl[ba2049ed27b9e923]::execution::try_execute_query::<rustc_middle[7183fb41e9311d8f]::query::caches::DefIdCache<rustc_middle[7183fb41e9311d8f]::query::erase::ErasedData<[u8; 8usize]>>, true>
  28:     0x7f9bf9c60f15 - rustc_query_impl[ba2049ed27b9e923]::query_impl::specialization_graph_of::execute_query_incr::__rust_end_short_backtrace
  29:     0x7f9bf8f0d805 - rustc_hir_analysis[771be2d3202827d0]::coherence::coherent_trait
  30:     0x7f9bf8f0d521 - rustc_query_impl[ba2049ed27b9e923]::query_impl::coherent_trait::invoke_provider_fn::__rust_begin_short_backtrace
  31:     0x7f9bf8f35fa2 - rustc_query_impl[ba2049ed27b9e923]::execution::try_execute_query::<rustc_middle[7183fb41e9311d8f]::query::caches::DefIdCache<rustc_middle[7183fb41e9311d8f]::query::erase::ErasedData<[u8; 1usize]>>, true>
  32:     0x7f9bf9809bcd - rustc_query_impl[ba2049ed27b9e923]::query_impl::coherent_trait::execute_query_incr::__rust_end_short_backtrace
  33:     0x7f9bf9a19169 - rustc_hir_analysis[771be2d3202827d0]::check::check::check_item_type
  34:     0x7f9bf9a10cf2 - rustc_hir_analysis[771be2d3202827d0]::check::wfcheck::check_well_formed
  35:     0x7f9bf9a10cd3 - rustc_query_impl[ba2049ed27b9e923]::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
  36:     0x7f9bf8f38d86 - rustc_query_impl[ba2049ed27b9e923]::execution::try_execute_query::<rustc_data_structures[86f60c62854a1a76]::vec_cache::VecCache<rustc_span[9b2c1fda2845f7b9]::def_id::LocalDefId, rustc_middle[7183fb41e9311d8f]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[7183fb41e9311d8f]::dep_graph::graph::DepNodeIndex>, true>
  37:     0x7f9bf8f383d1 - rustc_query_impl[ba2049ed27b9e923]::query_impl::check_well_formed::execute_query_incr::__rust_end_short_backtrace
  38:     0x7f9bf742bc2d - <rustc_middle[7183fb41e9311d8f]::hir::ModuleItems>::par_opaques::<rustc_hir_analysis[771be2d3202827d0]::check::wfcheck::check_type_wf::{closure#5}>::{closure#0}
  39:     0x7f9bf74d1d1b - <rustc_thread_pool[45e85249471ab754]::job::HeapJob<<rustc_thread_pool[45e85249471ab754]::scope::Scope>::spawn<rustc_data_structures[86f60c62854a1a76]::sync::parallel::par_slice<&rustc_hir[2f50cfae1daf0a82]::hir::ImplItemId, rustc_data_structures[86f60c62854a1a76]::sync::parallel::try_par_for_each_in<&[rustc_hir[2f50cfae1daf0a82]::hir::ImplItemId], rustc_span[9b2c1fda2845f7b9]::ErrorGuaranteed, <rustc_middle[7183fb41e9311d8f]::hir::ModuleItems>::par_impl_items<rustc_hir_analysis[771be2d3202827d0]::check::wfcheck::check_type_wf::{closure#1}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}::{closure#0}>::{closure#0}> as rustc_thread_pool[45e85249471ab754]::job::Job>::execute
  40:     0x7f9bf80f64bf - <rustc_thread_pool[45e85249471ab754]::registry::WorkerThread>::wait_or_steal_until_cold
  41:     0x7f9bf80f5062 - <rustc_thread_pool[45e85249471ab754]::registry::ThreadBuilder>::run
  42:     0x7f9bf72a20ec - std[f97f41f4b941f83d]::sys::backtrace::__rust_begin_short_backtrace::<<rustc_thread_pool[45e85249471ab754]::ThreadPoolBuilder>::build_scoped<rustc_interface[dd2c291cbeac3c6e]::util::run_in_thread_pool_with_globals<rustc_interface[dd2c291cbeac3c6e]::interface::run_compiler<(), rustc_driver_impl[94c2fdbf68adad86]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#0}, rustc_interface[dd2c291cbeac3c6e]::util::run_in_thread_pool_with_globals<rustc_interface[dd2c291cbeac3c6e]::interface::run_compiler<(), rustc_driver_impl[94c2fdbf68adad86]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
  43:     0x7f9bf72ab95a - <std[f97f41f4b941f83d]::thread::lifecycle::spawn_unchecked<<rustc_thread_pool[45e85249471ab754]::ThreadPoolBuilder>::build_scoped<rustc_interface[dd2c291cbeac3c6e]::util::run_in_thread_pool_with_globals<rustc_interface[dd2c291cbeac3c6e]::interface::run_compiler<(), rustc_driver_impl[94c2fdbf68adad86]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#0}, rustc_interface[dd2c291cbeac3c6e]::util::run_in_thread_pool_with_globals<rustc_interface[dd2c291cbeac3c6e]::interface::run_compiler<(), rustc_driver_impl[94c2fdbf68adad86]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>::{closure#1} as core[d89867bba8befc45]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  44:     0x7f9bf9ddeb52 - <std[f97f41f4b941f83d]::sys::thread::unix::Thread>::new::thread_start
  45:     0x7f9bf32981b9 - <unknown>
  46:     0x7f9bf331d21c - <unknown>
  47:                0x0 - <unknown>

error: 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: please make sure that you have updated to the latest nightly

note: rustc 1.98.0-nightly (42d7d5292 2026-06-15) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z incremental-verify-ich=yes -C incremental=[REDACTED] -C debuginfo=2 -C link-dead-code=true -Z validate-mir -Z query-dep-graph -Z threads=4

query stack during panic:
#0 [specialization_graph_of] building specialization graph of trait `Foobar`
#1 [coherent_trait] coherence checking all impls of trait `Foobar`
#2 [check_well_formed] checking that `<impl at /tmp/icemaker_global_tempdir.yqoNYHxs2mJh/rustc_testrunner_tmpdir_reporting.QC5ogv3zZwCi/mvce.rs:5:1: 5:55>` is well-formed
#3 [check_type_wf] checking that types are well-formed
#4 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 1 previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0601`.