[ICE]: region parameter .. out of range when instantiating

[matthiaskrgr]

auto-reduced (treereduce-rust):

//@compile-flags: -Znext-solver=globally
trait FinalSelfReturn {
    final fn self_return(&self) -> impl Sized {}
}
fn main() {
    let obj_return: &dyn FinalSelfReturn;
    obj_return.self_return();
}

original:

#![feature(final_associated_functions)]
trait FinalSelfReturn {
    final fn self_return(&self) -> impl Sized {}
}
fn main() {
    let obj_return: &dyn FinalSelfReturn;
    obj_return.self_return();
}

Version information

rustc 1.99.0-nightly (71c64160b 2026-07-09)
binary: rustc
commit-hash: 71c64160bd0f471bffdbdf7061fd62bab053d5b4
commit-date: 2026-07-09
host: x86_64-unknown-linux-gnu
release: 1.99.0-nightly
LLVM version: 22.1.8

Possibly related line of code:

rust/compiler/rustc_type_ir/src/binder.rs

Lines 887 to 899 in 71c6416

	)
	}
	#[cold]
	#[inline(never)]
	fn region_param_out_of_range(&self, ebr: I::EarlyParamRegion, r: I::Region) -> ! {
	panic!(
	"region parameter `{:?}` ({:?}/{}) out of range when instantiating args={:?}",
	ebr,
	r,
	ebr.index(),
	self.args,
	)

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Znext-solver=globally

Program output

error[E0658]: `final` on trait functions is experimental
 --> /tmp/icemaker_global_tempdir.r4Wz6AyZx5S3/rustc_testrunner_tmpdir_reporting.UZbl8yLdq2B5/mvce.rs:2:5
  |
2 |     final fn self_return(&self) -> impl Sized {}
  |     ^^^^^
  |
  = note: see issue #131179 <https://github.com/rust-lang/rust/issues/131179> for more information
  = help: add `#![feature(final_associated_functions)]` to the crate attributes to enable
  = note: this compiler was built on 2026-07-09; consider upgrading it if it is out of date


thread 'rustc' (765789) panicked at /rustc-dev/71c64160bd0f471bffdbdf7061fd62bab053d5b4/compiler/rustc_type_ir/src/binder.rs:893:9:
region parameter `'_/#1` ('_/#1/1) out of range when instantiating args=[dyn [Binder { value: Trait(FinalSelfReturn), bound_vars: [] }] + '!0]
stack backtrace:
   0:     0x7fd7438e4b06 - <<std[17923d02bb28d89c]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[bf6eba7c7efba28b]::fmt::Display>::fmt
   1:     0x7fd74400eede - core[bf6eba7c7efba28b]::fmt::write
   2:     0x7fd7438f9eec - <std[17923d02bb28d89c]::sys::stdio::unix::Stderr as std[17923d02bb28d89c]::io::Write>::write_fmt
   3:     0x7fd7438b8e0a - std[17923d02bb28d89c]::panicking::default_hook::{closure#0}
   4:     0x7fd7438d71c3 - std[17923d02bb28d89c]::panicking::default_hook
   5:     0x7fd7428bf148 - std[17923d02bb28d89c]::panicking::update_hook::<alloc[57d3a8d7fe6e581c]::boxed::Box<rustc_driver_impl[b4f847f556f8ec97]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fd7438d7662 - std[17923d02bb28d89c]::panicking::panic_with_hook
   7:     0x7fd7438b8ec2 - std[17923d02bb28d89c]::panicking::panic_handler::{closure#0}
   8:     0x7fd7438ad3a9 - std[17923d02bb28d89c]::sys::backtrace::__rust_end_short_backtrace::<std[17923d02bb28d89c]::panicking::panic_handler::{closure#0}, !>
   9:     0x7fd7438ba82d - __rustc[74db064d05eb3a7]::rust_begin_unwind
  10:     0x7fd740a1910c - core[bf6eba7c7efba28b]::panicking::panic_fmt
  11:     0x7fd742ea26d5 - <rustc_type_ir[7c6e04240091539c]::binder::ArgFolder<rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::region_param_out_of_range
  12:     0x7fd74404e373 - <rustc_type_ir[7c6e04240091539c]::binder::ArgFolder<rustc_middle[15e230250490b43e]::ty::context::TyCtxt> as rustc_type_ir[7c6e04240091539c]::fold::TypeFolder<rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::fold_ty
  13:     0x7fd744047903 - <rustc_middle[15e230250490b43e]::ty::predicate::Clause as rustc_type_ir[7c6e04240091539c]::fold::TypeFoldable<rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::fold_with::<rustc_type_ir[7c6e04240091539c]::binder::ArgFolder<rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>
  14:     0x7fd744d78ef0 - rustc_next_trait_solver[e63ddd75daf7c8da]::solve::assembly::structural_traits::predicates_for_object_candidate::<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>
  15:     0x7fd744d78950 - <rustc_type_ir[7c6e04240091539c]::predicate::TraitPredicate<rustc_middle[15e230250490b43e]::ty::context::TyCtxt> as rustc_next_trait_solver[e63ddd75daf7c8da]::solve::assembly::GoalKind<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::match_assumption::<<rustc_type_ir[7c6e04240091539c]::predicate::TraitPredicate<rustc_middle[15e230250490b43e]::ty::context::TyCtxt> as rustc_next_trait_solver[e63ddd75daf7c8da]::solve::assembly::GoalKind<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::probe_and_consider_object_bound_candidate::{closure#0}>
  16:     0x7fd744d7c8cc - <rustc_type_ir[7c6e04240091539c]::predicate::TraitPredicate<rustc_middle[15e230250490b43e]::ty::context::TyCtxt> as rustc_next_trait_solver[e63ddd75daf7c8da]::solve::assembly::GoalKind<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::probe_and_match_goal_against_assumption::<<rustc_type_ir[7c6e04240091539c]::predicate::TraitPredicate<rustc_middle[15e230250490b43e]::ty::context::TyCtxt> as rustc_next_trait_solver[e63ddd75daf7c8da]::solve::assembly::GoalKind<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::probe_and_consider_object_bound_candidate::{closure#0}>
  17:     0x7fd74554c115 - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::compute_trait_goal
  18:     0x7fd7451b9216 - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate> as rustc_type_ir[7c6e04240091539c]::search_graph::Delegate>::compute_goal::{closure#0}
  19:     0x7fd741254b13 - <rustc_type_ir[7c6e04240091539c]::search_graph::SearchGraph<rustc_next_trait_solver[e63ddd75daf7c8da]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate>, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}
  20:     0x7fd744d33e5b - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::evaluate_goal_cold
  21:     0x7fd744207d72 - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::evaluate_added_goals_step
  22:     0x7fd744d84f03 - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::evaluate_added_goals_and_make_canonical_response::{closure#0}
  23:     0x7fd7451b98d0 - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate> as rustc_type_ir[7c6e04240091539c]::search_graph::Delegate>::compute_goal::{closure#0}
  24:     0x7fd741254b13 - <rustc_type_ir[7c6e04240091539c]::search_graph::SearchGraph<rustc_next_trait_solver[e63ddd75daf7c8da]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate>, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}
  25:     0x7fd744d33e5b - <rustc_next_trait_solver[e63ddd75daf7c8da]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate, rustc_middle[15e230250490b43e]::ty::context::TyCtxt>>::evaluate_goal_cold
  26:     0x7fd744d33220 - <rustc_trait_selection[244cc590383734dc]::solve::delegate::SolverDelegate as rustc_next_trait_solver[e63ddd75daf7c8da]::solve::eval_ctxt::SolverDelegateEvalExt>::evaluate_root_goal
  27:     0x7fd74421018b - <rustc_trait_selection[244cc590383734dc]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[244cc590383734dc]::traits::FulfillmentError> as rustc_infer[6562bab0b11b09a7]::traits::engine::TraitEngine<rustc_trait_selection[244cc590383734dc]::traits::FulfillmentError>>::try_evaluate_obligations
  28:     0x7fd744416468 - <core[bf6eba7c7efba28b]::iter::adapters::filter::Filter<core[bf6eba7c7efba28b]::iter::adapters::map::Map<core[bf6eba7c7efba28b]::iter::adapters::filter::Filter<core[bf6eba7c7efba28b]::slice::iter::Iter<rustc_hir_typeck[a102fae51bb8b632]::method::probe::Candidate>, <rustc_hir_typeck[a102fae51bb8b632]::method::probe::ProbeContext>::consider_candidates::{closure#0}>, <rustc_hir_typeck[a102fae51bb8b632]::method::probe::ProbeContext>::consider_candidates::{closure#1}>, <rustc_hir_typeck[a102fae51bb8b632]::method::probe::ProbeContext>::consider_candidates::{closure#2}> as core[bf6eba7c7efba28b]::iter::traits::iterator::Iterator>::next
  29:     0x7fd74440cb0b - <rustc_hir_typeck[a102fae51bb8b632]::method::probe::ProbeContext>::pick_all_method
  30:     0x7fd74502b972 - <rustc_hir_typeck[a102fae51bb8b632]::fn_ctxt::FnCtxt>::lookup_probe
  31:     0x7fd7442c4aba - <rustc_hir_typeck[a102fae51bb8b632]::fn_ctxt::FnCtxt>::check_expr_method_call
  32:     0x7fd7442df900 - <rustc_hir_typeck[a102fae51bb8b632]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  33:     0x7fd7442b6433 - <rustc_hir_typeck[a102fae51bb8b632]::fn_ctxt::FnCtxt>::check_expr_block
  34:     0x7fd7442df92d - <rustc_hir_typeck[a102fae51bb8b632]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  35:     0x7fd74429688c - rustc_hir_typeck[a102fae51bb8b632]::check::check_fn
  36:     0x7fd744e81201 - rustc_hir_typeck[a102fae51bb8b632]::typeck_with_inspect::{closure#0}
  37:     0x7fd744e7fc00 - rustc_query_impl[d58a7b813a5b7f55]::query_impl::typeck_root::invoke_provider_fn::__rust_begin_short_backtrace
  38:     0x7fd7443f81a9 - rustc_query_impl[d58a7b813a5b7f55]::execution::try_execute_query::<rustc_data_structures[fd85311d7f0af68d]::vec_cache::VecCache<rustc_span[c5a5c3dd8ccfd604]::def_id::LocalDefId, rustc_middle[15e230250490b43e]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[15e230250490b43e]::dep_graph::graph::DepNodeIndex>, false>
  39:     0x7fd7443f7c03 - rustc_query_impl[d58a7b813a5b7f55]::query_impl::typeck_root::execute_query_non_incr::__rust_end_short_backtrace
  40:     0x7fd7443f5173 - <rustc_middle[15e230250490b43e]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[b04cde925e264121]::check_crate::{closure#1}>::{closure#0}
  41:     0x7fd7443f4ab1 - rustc_hir_analysis[b04cde925e264121]::check_crate
  42:     0x7fd7443f8eba - rustc_interface[e6f7a441c6fe091c]::passes::analysis
  43:     0x7fd745108387 - rustc_query_impl[d58a7b813a5b7f55]::execution::try_execute_query::<rustc_middle[15e230250490b43e]::query::caches::SingleCache<rustc_middle[15e230250490b43e]::query::erase::ErasedData<[u8; 0usize]>>, false>
  44:     0x7fd745108069 - rustc_query_impl[d58a7b813a5b7f55]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  45:     0x7fd745144140 - rustc_interface[e6f7a441c6fe091c]::interface::run_compiler::<(), rustc_driver_impl[b4f847f556f8ec97]::run_compiler::{closure#0}>::{closure#1}
  46:     0x7fd74511ccfa - std[17923d02bb28d89c]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e6f7a441c6fe091c]::util::run_in_thread_with_globals<rustc_interface[e6f7a441c6fe091c]::util::run_in_thread_pool_with_globals<rustc_interface[e6f7a441c6fe091c]::interface::run_compiler<(), rustc_driver_impl[b4f847f556f8ec97]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  47:     0x7fd74511caad - <std[17923d02bb28d89c]::thread::lifecycle::spawn_unchecked<rustc_interface[e6f7a441c6fe091c]::util::run_in_thread_with_globals<rustc_interface[e6f7a441c6fe091c]::util::run_in_thread_pool_with_globals<rustc_interface[e6f7a441c6fe091c]::interface::run_compiler<(), rustc_driver_impl[b4f847f556f8ec97]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[bf6eba7c7efba28b]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  48:     0x7fd745112e90 - <std[17923d02bb28d89c]::sys::thread::unix::Thread>::new::thread_start
  49:     0x7fd73ea981b9 - <unknown>
  50:     0x7fd73eb1d21c - <unknown>
  51:                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 1.99.0-nightly (71c64160b 2026-07-09) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z next-solver=globally -Z dump-mir-dir=dir

query stack during panic:
#0 [typeck_root] type-checking `main`
#1 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0658`.

@rustbot label +F-final_associated_functions +WG-trait-system-refactor

[matthiaskrgr]

old solver on

#![feature(final_associated_functions)]
trait FinalSelfReturn {
    final fn self_return(&self) -> impl Sized {}
}
fn main() {
    let obj_return: &dyn FinalSelfReturn;
    obj_return.self_return();
}

error[E0038]: the trait `FinalSelfReturn` is not dyn compatible
 --> code.rs:7:16
  |
7 |     obj_return.self_return();
  |                ^^^^^^^^^^^ `FinalSelfReturn` is not dyn compatible
  |
  = note: for a trait to be dyn compatible it needs to allow building a vtable
          for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

since #151783 🤷