rust-lang / rust-lang/rust

[ICE]: `discr subgoal`

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C-bug F-unsafe_binders I-ICE needs-triage T-compiler WG-trait-system-refactor
Dominant language
Rust
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Description

Code
// compiler-flags: -Znext-solver=globally
#![feature(unsafe_binders)]
fn foo<T: std::marker::Copy>(x: unsafe<> T) {
    std::mem::discriminant(&x);
}

fn main() {}
Meta

rustc --version --verbose:

rustc 1.99.0-nightly (3659db0d3 2026-07-05)
binary: rustc
commit-hash: 3659db0d3e2cd634c766fcda79ed118eca31a9fd
commit-date: 2026-07-05
host: x86_64-unknown-linux-gnu
release: 1.99.0-nightly
LLVM version: 22.1.8
Error output
<output>
Backtrace 

warning: the feature `unsafe_binders` is incomplete and may not be safe to use and/or cause compiler crashes
 --> k.rs:1:12
  |
1 | #![feature(unsafe_binders)]
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #130516 <https://github.com/rust-lang/rust/issues/130516> for more information
  = note: `#[warn(incomplete_features)]` on by default


thread 'rustc' (3853805) panicked at /rustc-dev/3659db0d3e2cd634c766fcda79ed118eca31a9fd/compiler/rustc_next_trait_solver/src/solve/normalizes_to.rs:1008:17:
not yet implemented: discr subgoal...
stack backtrace:
   0:     0x7f483ecd3846 - <<std[f3ff1fb6d3edc9aa]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[a41e0ab587117a37]::fmt::Display>::fmt
   1:     0x7f483f40ec9e - core[a41e0ab587117a37]::fmt::write
   2:     0x7f483ece8c2c - <std[f3ff1fb6d3edc9aa]::sys::stdio::unix::Stderr as std[f3ff1fb6d3edc9aa]::io::Write>::write_fmt
   3:     0x7f483eca7caa - std[f3ff1fb6d3edc9aa]::panicking::default_hook::{closure#0}
   4:     0x7f483ecc5f93 - std[f3ff1fb6d3edc9aa]::panicking::default_hook
   5:     0x7f483dcb51d8 - std[f3ff1fb6d3edc9aa]::panicking::update_hook::<alloc[63993826f7b5d124]::boxed::Box<rustc_driver_impl[1d9b408d7a24224d]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f483ecc6432 - std[f3ff1fb6d3edc9aa]::panicking::panic_with_hook
   7:     0x7f483eca7d94 - std[f3ff1fb6d3edc9aa]::panicking::panic_handler::{closure#0}
   8:     0x7f483ec9ea29 - std[f3ff1fb6d3edc9aa]::sys::backtrace::__rust_end_short_backtrace::<std[f3ff1fb6d3edc9aa]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f483eca96cd - __rustc[1b6846d77d192586]::rust_begin_unwind
  10:     0x7f483bd1e9ac - core[a41e0ab587117a37]::panicking::panic_fmt
  11:     0x7f4840a6da18 - <rustc_type_ir[be49fdf947711b1b]::predicate::NormalizesTo<rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt> as rustc_next_trait_solver[29a5c63578321cec]::solve::assembly::GoalKind<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::consider_builtin_discriminant_kind_candidate
  12:     0x7f48400f3a0a - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::assemble_and_evaluate_candidates::<rustc_type_ir[be49fdf947711b1b]::predicate::NormalizesTo<rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>
  13:     0x7f484062e5ec - <rustc_next_trait_solver[29a5c63578321cec]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate> as rustc_type_ir[be49fdf947711b1b]::search_graph::Delegate>::compute_goal::{closure#0}
  14:     0x7f483c6e0843 - <rustc_type_ir[be49fdf947711b1b]::search_graph::SearchGraph<rustc_next_trait_solver[29a5c63578321cec]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate>, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}
  15:     0x7f484017431b - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::evaluate_goal_cold
  16:     0x7f484062e178 - <rustc_next_trait_solver[29a5c63578321cec]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate> as rustc_type_ir[be49fdf947711b1b]::search_graph::Delegate>::compute_goal::{closure#0}
  17:     0x7f483c6e0843 - <rustc_type_ir[be49fdf947711b1b]::search_graph::SearchGraph<rustc_next_trait_solver[29a5c63578321cec]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate>, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}
  18:     0x7f484017431b - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::evaluate_goal_cold
  19:     0x7f48401719f8 - <rustc_next_trait_solver[29a5c63578321cec]::normalize::NormalizationFolder<rustc_infer[83676dc9fff0c021]::infer::InferCtxt, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt, <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::normalize<rustc_middle[67dc40c5dc90d8fe]::ty::predicate::Predicate>::{closure#0}> as rustc_type_ir[be49fdf947711b1b]::fold::FallibleTypeFolder<rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::try_fold_ty::{closure#0}
  20:     0x7f4840170ad8 - <&rustc_middle[67dc40c5dc90d8fe]::ty::list::RawList<(), rustc_middle[67dc40c5dc90d8fe]::ty::generic_args::GenericArg> as rustc_type_ir[be49fdf947711b1b]::fold::TypeFoldable<rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::try_fold_with::<rustc_next_trait_solver[29a5c63578321cec]::normalize::NormalizationFolder<rustc_infer[83676dc9fff0c021]::infer::InferCtxt, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt, <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::normalize<rustc_middle[67dc40c5dc90d8fe]::ty::predicate::Predicate>::{closure#0}>>
  21:     0x7f48400fe454 - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::add_goal
  22:     0x7f48400fbba7 - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::probe_and_evaluate_goal_for_constituent_tys::<<rustc_type_ir[be49fdf947711b1b]::predicate::TraitPredicate<rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt> as rustc_next_trait_solver[29a5c63578321cec]::solve::assembly::GoalKind<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::consider_builtin_sizedness_candidates::{closure#0}>
  23:     0x7f4840a5c12e - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::compute_trait_goal
  24:     0x7f484062d8d3 - <rustc_next_trait_solver[29a5c63578321cec]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate> as rustc_type_ir[be49fdf947711b1b]::search_graph::Delegate>::compute_goal::{closure#0}
  25:     0x7f483c6e0843 - <rustc_type_ir[be49fdf947711b1b]::search_graph::SearchGraph<rustc_next_trait_solver[29a5c63578321cec]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate>, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}
  26:     0x7f484017431b - <rustc_next_trait_solver[29a5c63578321cec]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[2948f6a729fb144b]::solve::delegate::SolverDelegate, rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>>::evaluate_goal_cold
  27:     0x7f4840181799 - <rustc_trait_selection[2948f6a729fb144b]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[2948f6a729fb144b]::traits::FulfillmentError> as rustc_infer[83676dc9fff0c021]::traits::engine::TraitEngine<rustc_trait_selection[2948f6a729fb144b]::traits::FulfillmentError>>::try_evaluate_obligations
  28:     0x7f48401b371d - rustc_hir_typeck[86bf61ef5573921e]::typeck_with_inspect::{closure#0}
  29:     0x7f48401ade00 - rustc_query_impl[44f1d94f3682cc0a]::query_impl::typeck_root::invoke_provider_fn::__rust_begin_short_backtrace
  30:     0x7f483f7f2be9 - rustc_query_impl[44f1d94f3682cc0a]::execution::try_execute_query::<rustc_data_structures[d344ec675b6e4243]::vec_cache::VecCache<rustc_span[e9819c9ffbcf2457]::def_id::LocalDefId, rustc_middle[67dc40c5dc90d8fe]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[67dc40c5dc90d8fe]::dep_graph::graph::DepNodeIndex>, false>
  31:     0x7f483f7f2643 - rustc_query_impl[44f1d94f3682cc0a]::query_impl::typeck_root::execute_query_non_incr::__rust_end_short_backtrace
  32:     0x7f483f7efba3 - <rustc_middle[67dc40c5dc90d8fe]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[3a159b81db3b0a1f]::check_crate::{closure#1}>::{closure#0}
  33:     0x7f483f7ef4e1 - rustc_hir_analysis[3a159b81db3b0a1f]::check_crate
  34:     0x7f483f7f38fa - rustc_interface[96ef288c905db9b6]::passes::analysis
  35:     0x7f484059e247 - rustc_query_impl[44f1d94f3682cc0a]::execution::try_execute_query::<rustc_middle[67dc40c5dc90d8fe]::query::caches::SingleCache<rustc_middle[67dc40c5dc90d8fe]::query::erase::ErasedData<[u8; 0usize]>>, false>
  36:     0x7f484059dea9 - rustc_query_impl[44f1d94f3682cc0a]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  37:     0x7f48405d6140 - rustc_interface[96ef288c905db9b6]::interface::run_compiler::<(), rustc_driver_impl[1d9b408d7a24224d]::run_compiler::{closure#0}>::{closure#1}
  38:     0x7f48405ad6fa - std[f3ff1fb6d3edc9aa]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[96ef288c905db9b6]::util::run_in_thread_with_globals<rustc_interface[96ef288c905db9b6]::util::run_in_thread_pool_with_globals<rustc_interface[96ef288c905db9b6]::interface::run_compiler<(), rustc_driver_impl[1d9b408d7a24224d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  39:     0x7f48405ad4ad - <std[f3ff1fb6d3edc9aa]::thread::lifecycle::spawn_unchecked<rustc_interface[96ef288c905db9b6]::util::run_in_thread_with_globals<rustc_interface[96ef288c905db9b6]::util::run_in_thread_pool_with_globals<rustc_interface[96ef288c905db9b6]::interface::run_compiler<(), rustc_driver_impl[1d9b408d7a24224d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[a41e0ab587117a37]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  40:     0x7f48405b18d0 - <std[f3ff1fb6d3edc9aa]::sys::thread::unix::Thread>::new::thread_start
  41:     0x7f4839e981b9 - <unknown>
  42:     0x7f4839f1d21c - <unknown>
  43:                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: please attach the file at `/tmp/im/j/rustc-ice-2026-07-06T04_54_21-3853795.txt` to your bug report

note: rustc 1.99.0-nightly (3659db0d3 2026-07-05) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z next-solver=globally

query stack during panic:
#0 [typeck_root] type-checking `foo`
#1 [analysis] running analysis passes on crate `k`
end of query stack

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Research direction

Run the supplied Rust reproducer with -Znext-solver=globally and the unsafe_binders feature to confirm the ICE. Start at compiler/rustc_next_trait_solver/src/solve/normalizes_to.rs around consider_builtin_discriminant_kind_candidate, reported near line 1008. Done means the example no longer panics and has regression coverage for this case.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
45/100

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