ICE: `entered unreachable code: PointeeSized is removed during lowering` with `-Z next-solver=globally` and recursive associated type bound

[trait-Cong]

I tried this code:
Reduction:

trait PointeeSized {
    type Undefined;
}
struct T;
impl PointeeSized for T
where
    <T as PointeeSized>::Undefined: PointeeSized,
{}
fn main() {}

Release channel	Result
Current Stable	error
Current Nightly (default solver)	error
Current Nightly (+ -Znext-solver=globally)	ICE

Meta

rustc --version --verbose:

rustc 1.95.0-nightly (a293cc4af 2026-01-30)
binary: rustc
commit-hash: a293cc4af8b26701c42738381c0c6f9d2ba881e0
commit-date: 2026-01-30
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 22.1.0

Backtrace

thread 'rustc' panicked at /rustc-dev/a293cc4af8b26701c42738381c0c6f9d2ba881e0/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs:550:21:
internal error: entered unreachable code: `PointeeSized` is removed during lowering
stack backtrace:
   0:     0x7f854c225b2b - <std[b56300d62699629]::backtrace::Backtrace>::create
   1:     0x7f854c225a75 - <std[b56300d62699629]::backtrace::Backtrace>::force_capture
   2:     0x7f854b20e06a - std[b56300d62699629]::panicking::update_hook::<alloc[77e06c05b3e1163]::boxed::Box<rustc_driver_impl[306165e0f22ac3b8]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7f854c238562 - std[b56300d62699629]::panicking::panic_with_hook
   4:     0x7f854c21b05a - std[b56300d62699629]::panicking::panic_handler::{closure#0}
   5:     0x7f854c20f599 - std[b56300d62699629]::sys::backtrace::__rust_end_short_backtrace::<std[b56300d62699629]::panicking::panic_handler::{closure#0}, !>
   6:     0x7f854c21ca8d - __rustc[dff7bba7b93d99f5]::rust_begin_unwind
   7:     0x7f8548ec973c - core[1940e17cfe77f04e]::panicking::panic_fmt
   8:     0x7f854d6bbb0f - <rustc_next_trait_solver[9292fa706aa7673a]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[c7f74c517c76c09d]::solve::delegate::SolverDelegate, rustc_middle[4fbddfd8361bbe31]::ty::context::TyCtxt>>::assemble_builtin_impl_candidates::<rustc_type_ir[d34b452a896e10b7]::predicate::TraitPredicate<rustc_middle[4fbddfd8361bbe31]::ty::context::TyCtxt>>
   9:     0x7f854d6ad8b3 - <rustc_next_trait_solver[9292fa706aa7673a]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[c7f74c517c76c09d]::solve::delegate::SolverDelegate, rustc_middle[4fbddfd8361bbe31]::ty::context::TyCtxt>>::compute_trait_goal
  10:     0x7f854d6a712b - <rustc_next_trait_solver[9292fa706aa7673a]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[c7f74c517c76c09d]::solve::delegate::SolverDelegate> as rustc_type_ir[d34b452a896e10b7]::search_graph::Delegate>::compute_goal::{closure#0}
  11:     0x7f854d3826ee - <rustc_next_trait_solver[9292fa706aa7673a]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[c7f74c517c76c09d]::solve::delegate::SolverDelegate, rustc_middle[4fbddfd8361bbe31]::ty::context::TyCtxt>>::evaluate_goal_raw
  12:     0x7f854d391cbc - <rustc_trait_selection[c7f74c517c76c09d]::solve::fulfill::FulfillmentCtxt<rustc_infer[a2c09121c28d14ae]::traits::engine::ScrubbedTraitError> as rustc_infer[a2c09121c28d14ae]::traits::engine::TraitEngine<rustc_infer[a2c09121c28d14ae]::traits::engine::ScrubbedTraitError>>::evaluate_obligations_error_on_ambiguity
  13:     0x7f854ceb4b4b - <rustc_infer[a2c09121c28d14ae]::infer::InferCtxt as rustc_trait_selection[c7f74c517c76c09d]::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation_no_overflow
  14:     0x7f854bfd2a12 - <core[1940e17cfe77f04e]::iter::adapters::flatten::FlattenCompat<_, _> as core[1940e17cfe77f04e]::iter::traits::iterator::Iterator>::try_fold::flatten::<core[1940e17cfe77f04e]::iter::adapters::copied::Copied<core[1940e17cfe77f04e]::slice::iter::Iter<rustc_span[40d3100df278a6ee]::def_id::DefId>>, (), core[1940e17cfe77f04e]::ops::control_flow::ControlFlow<rustc_span[40d3100df278a6ee]::def_id::DefId>, core[1940e17cfe77f04e]::iter::traits::iterator::Iterator::find::check<rustc_span[40d3100df278a6ee]::def_id::DefId, <rustc_trait_selection[c7f74c517c76c09d]::error_reporting::TypeErrCtxt>::check_same_name_different_path::{closure#1}>::{closure#0}>::{closure#0}
  15:     0x7f854bfd148c - core[1940e17cfe77f04e]::iter::adapters::map::map_try_fold::<rustc_span[40d3100df278a6ee]::def_id::CrateNum, core[1940e17cfe77f04e]::iter::adapters::copied::Copied<core[1940e17cfe77f04e]::slice::iter::Iter<rustc_span[40d3100df278a6ee]::def_id::DefId>>, (), core[1940e17cfe77f04e]::ops::control_flow::ControlFlow<rustc_span[40d3100df278a6ee]::def_id::DefId>, <rustc_middle[4fbddfd8361bbe31]::ty::context::TyCtxt>::all_traits_including_private::{closure#0}, <core[1940e17cfe77f04e]::iter::adapters::flatten::FlattenCompat<_, _>>::iter_try_fold::flatten<core[1940e17cfe77f04e]::iter::adapters::copied::Copied<core[1940e17cfe77f04e]::slice::iter::Iter<rustc_span[40d3100df278a6ee]::def_id::DefId>>, (), core[1940e17cfe77f04e]::ops::control_flow::ControlFlow<rustc_span[40d3100df278a6ee]::def_id::DefId>, <core[1940e17cfe77f04e]::iter::adapters::flatten::FlattenCompat<_, _> as core[1940e17cfe77f04e]::iter::traits::iterator::Iterator>::try_fold::flatten<core[1940e17cfe77f04e]::iter::adapters::copied::Copied<core[1940e17cfe77f04e]::slice::iter::Iter<rustc_span[40d3100df278a6ee]::def_id::DefId>>, (), core[1940e17cfe77f04e]::ops::control_flow::ControlFlow<rustc_span[40d3100df278a6ee]::def_id::DefId>, core[1940e17cfe77f04e]::iter::traits::iterator::Iterator::find::check<rustc_span[40d3100df278a6ee]::def_id::DefId, <rustc_trait_selection[c7f74c517c76c09d]::error_reporting::TypeErrCtxt>::check_same_name_different_path::{closure#1}>::{closure#0}>::{closure#0}>::{closure#0}>::{closure#0}
  16:     0x7f854c0319ff - <rustc_trait_selection[c7f74c517c76c09d]::error_reporting::TypeErrCtxt>::note_different_trait_with_same_name
  17:     0x7f854c013011 - <rustc_trait_selection[c7f74c517c76c09d]::error_reporting::TypeErrCtxt>::report_selection_error
  18:     0x7f854ab238f7 - <rustc_trait_selection[c7f74c517c76c09d]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  19:     0x7f854d14a819 - rustc_hir_analysis[281f645d6dd33d26]::check::wfcheck::check_impl
  20:     0x7f854cf1fd61 - rustc_hir_analysis[281f645d6dd33d26]::check::check::check_item_type
  21:     0x7f854cf1c034 - rustc_hir_analysis[281f645d6dd33d26]::check::wfcheck::check_well_formed
  22:     0x7f854cf1c015 - rustc_query_impl[de8dc5dcbfafa282]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[de8dc5dcbfafa282]::query_impl::check_well_formed::make_query_vtable::{closure#1}::{closure#0}, rustc_middle[4fbddfd8361bbe31]::query::erase::ErasedData<[u8; 1usize]>>
  23:     0x7f854cf1ba33 - rustc_query_system[47e010d69cf1376c]::query::plumbing::try_execute_query::<rustc_query_impl[de8dc5dcbfafa282]::SemiDynamicQueryDispatcher<rustc_data_structures[66bcb0d8d60a0708]::vec_cache::VecCache<rustc_span[40d3100df278a6ee]::def_id::LocalDefId, rustc_middle[4fbddfd8361bbe31]::query::erase::ErasedData<[u8; 1usize]>, rustc_query_system[47e010d69cf1376c]::dep_graph::graph::DepNodeIndex>, false, false, false>, false>
  24:     0x7f854cf1b542 - rustc_query_impl[de8dc5dcbfafa282]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  25:     0x7f854cf18cf0 - rustc_hir_analysis[281f645d6dd33d26]::check::wfcheck::check_type_wf
  26:     0x7f854cf18bdd - rustc_query_impl[de8dc5dcbfafa282]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[de8dc5dcbfafa282]::query_impl::check_type_wf::make_query_vtable::{closure#1}::{closure#0}, rustc_middle[4fbddfd8361bbe31]::query::erase::ErasedData<[u8; 1usize]>>
  27:     0x7f854d96d248 - rustc_query_system[47e010d69cf1376c]::query::plumbing::try_execute_query::<rustc_query_impl[de8dc5dcbfafa282]::SemiDynamicQueryDispatcher<rustc_query_system[47e010d69cf1376c]::query::caches::SingleCache<rustc_middle[4fbddfd8361bbe31]::query::erase::ErasedData<[u8; 1usize]>>, false, false, false>, false>
  28:     0x7f854d96cef6 - rustc_query_impl[de8dc5dcbfafa282]::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f854ce3fb56 - rustc_hir_analysis[281f645d6dd33d26]::check_crate
  30:     0x7f854c92e11b - rustc_interface[c33df4e5b4e639ae]::passes::analysis
  31:     0x7f854c92dd75 - rustc_query_impl[de8dc5dcbfafa282]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[de8dc5dcbfafa282]::query_impl::analysis::make_query_vtable::{closure#1}::{closure#0}, rustc_middle[4fbddfd8361bbe31]::query::erase::ErasedData<[u8; 0usize]>>
  32:     0x7f854d96dfe6 - rustc_query_system[47e010d69cf1376c]::query::plumbing::try_execute_query::<rustc_query_impl[de8dc5dcbfafa282]::SemiDynamicQueryDispatcher<rustc_query_system[47e010d69cf1376c]::query::caches::SingleCache<rustc_middle[4fbddfd8361bbe31]::query::erase::ErasedData<[u8; 0usize]>>, false, false, false>, false>
  33:     0x7f854d96ddce - rustc_query_impl[de8dc5dcbfafa282]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  34:     0x7f854db06b6c - <rustc_interface[c33df4e5b4e639ae]::passes::create_and_enter_global_ctxt<core[1940e17cfe77f04e]::option::Option<rustc_interface[c33df4e5b4e639ae]::queries::Linker>, rustc_driver_impl[306165e0f22ac3b8]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[1940e17cfe77f04e]::ops::function::FnOnce<(&rustc_session[1d337842f56cc0a6]::session::Session, rustc_middle[4fbddfd8361bbe31]::ty::context::CurrentGcx, alloc[77e06c05b3e1163]::sync::Arc<rustc_data_structures[66bcb0d8d60a0708]::jobserver::Proxy>, &std[b56300d62699629]::sync::once_lock::OnceLock<rustc_middle[4fbddfd8361bbe31]::ty::context::GlobalCtxt>, &rustc_data_structures[66bcb0d8d60a0708]::sync::worker_local::WorkerLocal<rustc_middle[4fbddfd8361bbe31]::arena::Arena>, &rustc_data_structures[66bcb0d8d60a0708]::sync::worker_local::WorkerLocal<rustc_hir[5322f89bbdf6d77c]::Arena>, rustc_driver_impl[306165e0f22ac3b8]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  35:     0x7f854d995748 - rustc_interface[c33df4e5b4e639ae]::interface::run_compiler::<(), rustc_driver_impl[306165e0f22ac3b8]::run_compiler::{closure#0}>::{closure#1}
  36:     0x7f854d9d25be - std[b56300d62699629]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[c33df4e5b4e639ae]::util::run_in_thread_with_globals<rustc_interface[c33df4e5b4e639ae]::util::run_in_thread_pool_with_globals<rustc_interface[c33df4e5b4e639ae]::interface::run_compiler<(), rustc_driver_impl[306165e0f22ac3b8]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  37:     0x7f854d9d2ae0 - <std[b56300d62699629]::thread::lifecycle::spawn_unchecked<rustc_interface[c33df4e5b4e639ae]::util::run_in_thread_with_globals<rustc_interface[c33df4e5b4e639ae]::util::run_in_thread_pool_with_globals<rustc_interface[c33df4e5b4e639ae]::interface::run_compiler<(), rustc_driver_impl[306165e0f22ac3b8]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[1940e17cfe77f04e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7f854d9d396c - <std[b56300d62699629]::sys::thread::unix::Thread>::new::thread_start
  39:     0x7f8547294ac3 - start_thread
                               at ./nptl/pthread_create.c:442:8
  40:     0x7f85473268c0 - __GI___clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81:0
  41:                0x0 - <unknown>


rustc version: 1.95.0-nightly (a293cc4af 2026-01-30)
platform: x86_64-unknown-linux-gnu

query stack during panic:
#0 [check_well_formed] checking that `<impl at bug.rs:5:1: 7:50>` is well-formed
#1 [check_type_wf] checking that types are well-formed
#2 [analysis] running analysis passes on crate `bug`
end of query stack

@rustbot label +WG-trait-system-refactor +I-ICE +T-compiler +C-bug

[theemathas]

This code ICEs on 1.93.0 and on nightly, with the default solver. However, it produces a normal compile error on 1.92.0.

Note that it seems to happen only when there's a user-defined trait named PointeeSized.

trait PointeeSized {}

trait Trait {}

impl Trait for i32 where
    i32: PointeeSized
{}

fn main() {}

[theemathas]

Bisection result:

searched nightlies: from nightly-2025-10-24 to nightly-2025-12-05
regressed nightly: nightly-2025-11-13
searched commit range: 25d319a...0186755
regressed commit: 11339a0

bisected with cargo-bisect-rustc v0.6.11

Host triple: aarch64-apple-darwin
Reproduce with:

cargo bisect-rustc --regress=ice --start=1.92.0 --end=1.93.0

---

Regressed in #144674. cc @rperier, @lcnr