rust-lang / rust-lang/rust

[ICE]: `layout_of: unexpected const: ?0c`

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

Code
// -Znext-solver=globally
#![feature(transmutability)]
use std::mem::TransmuteFrom;
fn array_like<T, E, const N: usize>()
where
    [E; N]: TransmuteFrom<T>,
{
}

fn main() {
    struct Struct;
    array_like::<Struct, u8, ()>;
}
Meta

rustc --version --verbose:

rustc 1.95.0-nightly (c7f5f3e0d 2026-02-07)
binary: rustc
commit-hash: c7f5f3e0d5defe632d44743cbaed56272e2b67f0
commit-date: 2026-02-07
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 22.1.0
Error output

rustc a.rs -Znext-solver=globally

<output>
Backtrace 

error[E0747]: type provided when a constant was expected
  --> a.rs:11:30
   |
11 |     array_like::<Struct, u8, ()>;
   |                              ^^

error: internal compiler error: /rustc-dev/c7f5f3e0d5defe632d44743cbaed56272e2b67f0/compiler/rustc_ty_utils/src/layout.rs:173:13: layout_of: unexpected const: ?0c


thread 'rustc' (3869519) panicked at /rustc-dev/c7f5f3e0d5defe632d44743cbaed56272e2b67f0/compiler/rustc_ty_utils/src/layout.rs:173:13:
Box<dyn Any>
stack backtrace:
   0:     0x7f25161e5a6b - <<std[12e671b2ab06fb6e]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[81298f05583b4988]::fmt::Display>::fmt
   1:     0x7f251680f048 - core[81298f05583b4988]::fmt::write
   2:     0x7f25161fcd56 - <std[12e671b2ab06fb6e]::sys::stdio::unix::Stderr as std[12e671b2ab06fb6e]::io::Write>::write_fmt
   3:     0x7f25161bba88 - std[12e671b2ab06fb6e]::panicking::default_hook::{closure#0}
   4:     0x7f25161d8e63 - std[12e671b2ab06fb6e]::panicking::default_hook
   5:     0x7f25151bc5f7 - std[12e671b2ab06fb6e]::panicking::update_hook::<alloc[acd192c11bf9e878]::boxed::Box<rustc_driver_impl[73ec0cfeb46ae4b6]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f25161d9142 - std[12e671b2ab06fb6e]::panicking::panic_with_hook
   7:     0x7f25151f0a51 - std[12e671b2ab06fb6e]::panicking::begin_panic::<rustc_errors[1a3e1ed3e530bdbd]::ExplicitBug>::{closure#0}
   8:     0x7f25151e94a6 - std[12e671b2ab06fb6e]::sys::backtrace::__rust_end_short_backtrace::<std[12e671b2ab06fb6e]::panicking::begin_panic<rustc_errors[1a3e1ed3e530bdbd]::ExplicitBug>::{closure#0}, !>
   9:     0x7f25151e6bb8 - std[12e671b2ab06fb6e]::panicking::begin_panic::<rustc_errors[1a3e1ed3e530bdbd]::ExplicitBug>
  10:     0x7f25151fc1d1 - <rustc_errors[1a3e1ed3e530bdbd]::diagnostic::BugAbort as rustc_errors[1a3e1ed3e530bdbd]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7f25157accc9 - rustc_middle[572c70537083e946]::util::bug::opt_span_bug_fmt::<rustc_span[8ab66f3eafd11b9d]::span_encoding::Span>::{closure#0}
  12:     0x7f25157ace52 - rustc_middle[572c70537083e946]::ty::context::tls::with_opt::<rustc_middle[572c70537083e946]::util::bug::opt_span_bug_fmt<rustc_span[8ab66f3eafd11b9d]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7f251579dfab - rustc_middle[572c70537083e946]::ty::context::tls::with_context_opt::<rustc_middle[572c70537083e946]::ty::context::tls::with_opt<rustc_middle[572c70537083e946]::util::bug::opt_span_bug_fmt<rustc_span[8ab66f3eafd11b9d]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7f2512cf72d4 - rustc_middle[572c70537083e946]::util::bug::bug_fmt
  15:     0x7f25184d8ef5 - rustc_ty_utils[35e41edb7db416b4]::layout::extract_const_value.cold
  16:     0x7f25171bd8bf - rustc_ty_utils[35e41edb7db416b4]::layout::layout_of_uncached
  17:     0x7f25171b4149 - rustc_ty_utils[35e41edb7db416b4]::layout::layout_of
  18:     0x7f25171b40a7 - rustc_query_impl[25c8ab03434e8ec6]::query_impl::layout_of::compute_fn::__rust_begin_short_backtrace
  19:     0x7f25171b3134 - rustc_query_system[5619a4a14f53d2]::query::plumbing::try_execute_query::<rustc_query_impl[25c8ab03434e8ec6]::SemiDynamicQueryDispatcher<rustc_query_system[5619a4a14f53d2]::query::caches::DefaultCache<rustc_middle[572c70537083e946]::ty::PseudoCanonicalInput<rustc_middle[572c70537083e946]::ty::Ty>, rustc_middle[572c70537083e946]::query::erase::ErasedData<[u8; 16usize]>>, {rustc_query_impl[25c8ab03434e8ec6]::QueryFlags { is_anon: false, is_depth_limit: true, is_feedable: false }}>, false>
  20:     0x7f25171b2d74 - rustc_query_impl[25c8ab03434e8ec6]::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
  21:     0x7f2516106e4f - rustc_transmute[c78959dded7601a6]::layout::rustc::layout_of
  22:     0x7f2516104ed2 - <rustc_transmute[c78959dded7601a6]::layout::tree::Tree<rustc_transmute[c78959dded7601a6]::layout::rustc::Def, rustc_middle[572c70537083e946]::ty::region::Region, rustc_middle[572c70537083e946]::ty::Ty>>::from_ty
  23:     0x7f25160fe904 - <rustc_transmute[c78959dded7601a6]::rustc::TransmuteTypeEnv>::is_transmutable
  24:     0x7f2516031bd5 - <rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate as rustc_next_trait_solver[b3345a89d684dc63]::delegate::SolverDelegate>::is_transmutable
  25:     0x7f2515510ea4 - <rustc_type_ir[41dc425a4a83a9d6]::predicate::TraitPredicate<rustc_middle[572c70537083e946]::ty::context::TyCtxt> as rustc_next_trait_solver[b3345a89d684dc63]::solve::assembly::GoalKind<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate, rustc_middle[572c70537083e946]::ty::context::TyCtxt>>::consider_builtin_transmute_candidate
  26:     0x7f2517720e2f - <rustc_next_trait_solver[b3345a89d684dc63]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate, rustc_middle[572c70537083e946]::ty::context::TyCtxt>>::assemble_builtin_impl_candidates::<rustc_type_ir[41dc425a4a83a9d6]::predicate::TraitPredicate<rustc_middle[572c70537083e946]::ty::context::TyCtxt>>
  27:     0x7f2517740c50 - <rustc_next_trait_solver[b3345a89d684dc63]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate, rustc_middle[572c70537083e946]::ty::context::TyCtxt>>::assemble_and_evaluate_candidates::<rustc_type_ir[41dc425a4a83a9d6]::predicate::TraitPredicate<rustc_middle[572c70537083e946]::ty::context::TyCtxt>>
  28:     0x7f2517758169 - <rustc_next_trait_solver[b3345a89d684dc63]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate, rustc_middle[572c70537083e946]::ty::context::TyCtxt>>::compute_trait_goal
  29:     0x7f2517753956 - <rustc_next_trait_solver[b3345a89d684dc63]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate> as rustc_type_ir[41dc425a4a83a9d6]::search_graph::Delegate>::compute_goal::{closure#0}
  30:     0x7f25177529cd - <rustc_type_ir[41dc425a4a83a9d6]::search_graph::SearchGraph<rustc_next_trait_solver[b3345a89d684dc63]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate>, rustc_middle[572c70537083e946]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}::{closure#2}
  31:     0x7f25174824ab - <rustc_next_trait_solver[b3345a89d684dc63]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[447f93b904961586]::solve::delegate::SolverDelegate, rustc_middle[572c70537083e946]::ty::context::TyCtxt>>::evaluate_goal_raw
  32:     0x7f2517302e33 - <rustc_trait_selection[447f93b904961586]::solve::fulfill::FulfillmentCtxt<rustc_trait_selection[447f93b904961586]::traits::FulfillmentError> as rustc_infer[db6aea443443cbd5]::traits::engine::TraitEngine<rustc_trait_selection[447f93b904961586]::traits::FulfillmentError>>::try_evaluate_obligations
  33:     0x7f2516d16917 - <rustc_hir_typeck[f21717366f0acd5]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  34:     0x7f2516d1b030 - <rustc_hir_typeck[f21717366f0acd5]::fn_ctxt::FnCtxt>::check_expr_block
  35:     0x7f2516d15dc4 - <rustc_hir_typeck[f21717366f0acd5]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  36:     0x7f2516d597fd - rustc_hir_typeck[f21717366f0acd5]::check::check_fn
  37:     0x7f25174cb33e - rustc_hir_typeck[f21717366f0acd5]::typeck_with_inspect::{closure#0}
  38:     0x7f25174c9d70 - rustc_query_impl[25c8ab03434e8ec6]::query_impl::typeck::compute_fn::__rust_begin_short_backtrace
  39:     0x7f25174c0e76 - rustc_query_system[5619a4a14f53d2]::query::plumbing::try_execute_query::<rustc_query_impl[25c8ab03434e8ec6]::SemiDynamicQueryDispatcher<rustc_data_structures[8538babf9bd6a81d]::vec_cache::VecCache<rustc_span[8ab66f3eafd11b9d]::def_id::LocalDefId, rustc_middle[572c70537083e946]::query::erase::ErasedData<[u8; 8usize]>, rustc_query_system[5619a4a14f53d2]::dep_graph::graph::DepNodeIndex>, {rustc_query_impl[25c8ab03434e8ec6]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}>, false>
  40:     0x7f25174c0a49 - rustc_query_impl[25c8ab03434e8ec6]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  41:     0x7f25174b86a0 - <rustc_middle[572c70537083e946]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[e2937b89f0871be1]::check_crate::{closure#2}>::{closure#0}
  42:     0x7f25174b80c0 - rustc_hir_analysis[e2937b89f0871be1]::check_crate
  43:     0x7f25174bc09b - rustc_interface[5e14f3d1b07b7995]::passes::analysis
  44:     0x7f2517a6b448 - rustc_query_system[5619a4a14f53d2]::query::plumbing::try_execute_query::<rustc_query_impl[25c8ab03434e8ec6]::SemiDynamicQueryDispatcher<rustc_query_system[5619a4a14f53d2]::query::caches::SingleCache<rustc_middle[572c70537083e946]::query::erase::ErasedData<[u8; 0usize]>>, {rustc_query_impl[25c8ab03434e8ec6]::QueryFlags { is_anon: false, is_depth_limit: false, is_feedable: false }}>, false>
  45:     0x7f2517a6b18a - rustc_query_impl[25c8ab03434e8ec6]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  46:     0x7f2517ba8ce7 - <rustc_interface[5e14f3d1b07b7995]::passes::create_and_enter_global_ctxt<core[81298f05583b4988]::option::Option<rustc_interface[5e14f3d1b07b7995]::queries::Linker>, rustc_driver_impl[73ec0cfeb46ae4b6]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[81298f05583b4988]::ops::function::FnOnce<(&rustc_session[9ad62f87fcf6845b]::session::Session, rustc_middle[572c70537083e946]::ty::context::CurrentGcx, alloc[acd192c11bf9e878]::sync::Arc<rustc_data_structures[8538babf9bd6a81d]::jobserver::Proxy>, &std[12e671b2ab06fb6e]::sync::once_lock::OnceLock<rustc_middle[572c70537083e946]::ty::context::GlobalCtxt>, &rustc_data_structures[8538babf9bd6a81d]::sync::worker_local::WorkerLocal<rustc_middle[572c70537083e946]::arena::Arena>, &rustc_data_structures[8538babf9bd6a81d]::sync::worker_local::WorkerLocal<rustc_hir[6d1544d29c786899]::Arena>, rustc_driver_impl[73ec0cfeb46ae4b6]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  47:     0x7f25179fdfa8 - rustc_interface[5e14f3d1b07b7995]::interface::run_compiler::<(), rustc_driver_impl[73ec0cfeb46ae4b6]::run_compiler::{closure#0}>::{closure#1}
  48:     0x7f2517a555fe - std[12e671b2ab06fb6e]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5e14f3d1b07b7995]::util::run_in_thread_with_globals<rustc_interface[5e14f3d1b07b7995]::util::run_in_thread_pool_with_globals<rustc_interface[5e14f3d1b07b7995]::interface::run_compiler<(), rustc_driver_impl[73ec0cfeb46ae4b6]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  49:     0x7f2517a55b20 - <std[12e671b2ab06fb6e]::thread::lifecycle::spawn_unchecked<rustc_interface[5e14f3d1b07b7995]::util::run_in_thread_with_globals<rustc_interface[5e14f3d1b07b7995]::util::run_in_thread_pool_with_globals<rustc_interface[5e14f3d1b07b7995]::interface::run_compiler<(), rustc_driver_impl[73ec0cfeb46ae4b6]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[81298f05583b4988]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  50:     0x7f2517a569ac - <std[12e671b2ab06fb6e]::sys::thread::unix::Thread>::new::thread_start
  51:     0x7f251129698b - <unknown>
  52:     0x7f251131a9cc - <unknown>
  53:                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: please make sure that you have updated to the latest nightly

note: please attach the file at `/tmp/im/4/rustc-ice-2026-02-08T11_41_06-3869501.txt` to your bug report

note: rustc 1.95.0-nightly (c7f5f3e0d 2026-02-07) running on x86_64-unknown-linux-gnu

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

query stack during panic:
panicked at /rustc-dev/c7f5f3e0d5defe632d44743cbaed56272e2b67f0/compiler/rustc_type_ir/src/const_kind.rs:124:17:

thread panicked while processing panic. aborting.
[1]    3869501 IOT instruction  rustc a.rs -Znext-solver=globally

Contributor guide

Open the contributing guide

First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the issue with the provided a.rs example using rustc a.rs -Znext-solver=globally. Start at rustc_ty_utils/src/layout.rs:173 and follow the layout_of and rustc_transmute stack entries shown in the backtrace. Done means this example no longer triggers the internal compiler error.

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
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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