ICE: valtrees: 'called `Result::unwrap()` on an `Err` value: ReferencesError(ErrorGuaranteed(()))'

[matthiaskrgr]

snippet:

#![feature(generic_const_exprs)]
#![feature(min_generic_const_args)]

fn pass_enum<const N : usize, const M : usize = const {N}> {
  pass_enum::<{None}>
}

Version information

rustc 1.94.0-nightly (08f833aa1 2026-01-11)
binary: rustc
commit-hash: 08f833aa179952037d5d0c5d949d4c3ec18ec212
commit-date: 2026-01-11
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8

Possibly related line of code:

rust/compiler/rustc_const_eval/src/const_eval/valtrees.rs

Lines 292 to 304 in 08f833a

	imm,
	tcx.layout_of(typing_env.as_query_input(cv.ty)).unwrap(),
	);
	op_to_const(&ecx, &imm.into(), /* for diagnostics */ false)
	}
	ty::Tuple(_) | ty::Array(_, _) | ty::Adt(..) => {
	let layout = tcx.layout_of(typing_env.as_query_input(cv.ty)).unwrap();
	if layout.is_zst() {
	// Fast path to avoid some allocations.
	return mir::ConstValue::ZeroSized;
	}
	if layout.backend_repr.is_scalar()
	&& (matches!(cv.ty.kind(), ty::Tuple(_))

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error: missing parameters for function definition
 --> /tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/mvce.rs:4:59
  |
4 | fn pass_enum<const N : usize, const M : usize = const {N}> {
  |                                                           ^
  |
help: add a parameter list
  |
4 | fn pass_enum<const N : usize, const M : usize = const {N}>() {
  |                                                           ++

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/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

warning: the feature `min_generic_const_args` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/mvce.rs:2:12
  |
2 | #![feature(min_generic_const_args)]
  |            ^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #132980 <https://github.com/rust-lang/rust/issues/132980> for more information

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/mvce.rs:6:2
  |
6 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/mvce.rs`

error: defaults for generic parameters are not allowed here
 --> /tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/mvce.rs:4:31
  |
4 | fn pass_enum<const N : usize, const M : usize = const {N}> {
  |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0107]: missing generics for enum `Option`
   --> /tmp/icemaker_global_tempdir.5bj3Sy84Vvk6/rustc_testrunner_tmpdir_reporting.4zX0bTSOQEzX/mvce.rs:5:16
    |
  5 |   pass_enum::<{None}>
    |                ^^^^ expected 1 generic argument
    |
note: enum defined here, with 1 generic parameter: `T`
   --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/option.rs:600:10
    |
600 | pub enum Option<T> {
    |          ^^^^^^ -
help: add missing generic argument
    |
  5 |   pass_enum::<{None<T>}>
    |                    +++


thread 'rustc' (4047645) panicked at /rustc-dev/08f833aa179952037d5d0c5d949d4c3ec18ec212/compiler/rustc_const_eval/src/const_eval/valtrees.rs:298:74:
called `Result::unwrap()` on an `Err` value: ReferencesError(ErrorGuaranteed(()))
stack backtrace:
   0:     0x7f5d4923fb73 - <<std[4ef27b15e8c8b39f]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[9b0602b26cbac703]::fmt::Display>::fmt
   1:     0x7f5d4980e308 - core[9b0602b26cbac703]::fmt::write
   2:     0x7f5d49255df6 - <std[4ef27b15e8c8b39f]::sys::stdio::unix::Stderr as std[4ef27b15e8c8b39f]::io::Write>::write_fmt
   3:     0x7f5d49215d48 - std[4ef27b15e8c8b39f]::panicking::default_hook::{closure#0}
   4:     0x7f5d49233403 - std[4ef27b15e8c8b39f]::panicking::default_hook
   5:     0x7f5d48216c4a - std[4ef27b15e8c8b39f]::panicking::update_hook::<alloc[be64b5636c6ea185]::boxed::Box<rustc_driver_impl[cb5a0d29d79f9b0b]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f5d492336e2 - std[4ef27b15e8c8b39f]::panicking::panic_with_hook
   7:     0x7f5d49215e08 - std[4ef27b15e8c8b39f]::panicking::panic_handler::{closure#0}
   8:     0x7f5d4920a2b9 - std[4ef27b15e8c8b39f]::sys::backtrace::__rust_end_short_backtrace::<std[4ef27b15e8c8b39f]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f5d492178dd - __rustc[4141da0a4ce75b43]::rust_begin_unwind
  10:     0x7f5d465f905c - core[9b0602b26cbac703]::panicking::panic_fmt
  11:     0x7f5d45ad3e82 - core[9b0602b26cbac703]::result::unwrap_failed
  12:     0x7f5d4a8643b4 - rustc_const_eval[a6a538f77ed30324]::const_eval::valtrees::valtree_to_const_value
  13:     0x7f5d4a863b2b - <rustc_const_eval[a6a538f77ed30324]::provide::{closure#1} as core[9b0602b26cbac703]::ops::function::FnOnce<(rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt, rustc_middle[927fbe768a54bf94]::ty::consts::valtree::Value)>>::call_once
  14:     0x7f5d4a863ad6 - rustc_query_impl[5c216bf84e04a0c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5c216bf84e04a0c]::query_impl::valtree_to_const_val::dynamic_query::{closure#2}::{closure#0}, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 24usize]>>
  15:     0x7f5d4a863a9f - <rustc_query_impl[5c216bf84e04a0c]::query_impl::valtree_to_const_val::dynamic_query::{closure#2} as core[9b0602b26cbac703]::ops::function::FnOnce<(rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt, rustc_middle[927fbe768a54bf94]::ty::consts::valtree::Value)>>::call_once
  16:     0x7f5d4a8630cc - rustc_query_system[d2dd35691c1a46d5]::query::plumbing::try_execute_query::<rustc_query_impl[5c216bf84e04a0c]::DynamicConfig<rustc_query_system[d2dd35691c1a46d5]::query::caches::DefaultCache<rustc_middle[927fbe768a54bf94]::ty::consts::valtree::Value, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[5c216bf84e04a0c]::plumbing::QueryCtxt, false>
  17:     0x7f5d4a862df5 - rustc_query_impl[5c216bf84e04a0c]::query_impl::valtree_to_const_val::get_query_non_incr::__rust_end_short_backtrace
  18:     0x7f5d4a88259a - <rustc_middle[927fbe768a54bf94]::mir::consts::Const>::eval
  19:     0x7f5d4a885984 - rustc_const_eval[a6a538f77ed30324]::const_eval::eval_queries::eval_to_allocation_raw_provider
  20:     0x7f5d4a884a46 - rustc_query_impl[5c216bf84e04a0c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5c216bf84e04a0c]::query_impl::eval_to_allocation_raw::dynamic_query::{closure#2}::{closure#0}, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 24usize]>>
  21:     0x7f5d4a88419f - rustc_query_system[d2dd35691c1a46d5]::query::plumbing::try_execute_query::<rustc_query_impl[5c216bf84e04a0c]::DynamicConfig<rustc_query_system[d2dd35691c1a46d5]::query::caches::DefaultCache<rustc_middle[927fbe768a54bf94]::ty::PseudoCanonicalInput<rustc_middle[927fbe768a54bf94]::mir::interpret::GlobalId>, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[5c216bf84e04a0c]::plumbing::QueryCtxt, false>
  22:     0x7f5d4a883d49 - rustc_query_impl[5c216bf84e04a0c]::query_impl::eval_to_allocation_raw::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7f5d4a869345 - rustc_const_eval[a6a538f77ed30324]::const_eval::valtrees::eval_to_valtree
  24:     0x7f5d4a8690f6 - <rustc_const_eval[a6a538f77ed30324]::provide::{closure#0} as core[9b0602b26cbac703]::ops::function::FnOnce<(rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt, rustc_middle[927fbe768a54bf94]::ty::PseudoCanonicalInput<rustc_middle[927fbe768a54bf94]::mir::interpret::GlobalId>)>>::call_once
  25:     0x7f5d4a8690c0 - rustc_query_impl[5c216bf84e04a0c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5c216bf84e04a0c]::query_impl::eval_to_valtree::dynamic_query::{closure#2}::{closure#0}, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 16usize]>>
  26:     0x7f5d4a86907b - <rustc_query_impl[5c216bf84e04a0c]::query_impl::eval_to_valtree::dynamic_query::{closure#2} as core[9b0602b26cbac703]::ops::function::FnOnce<(rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt, rustc_middle[927fbe768a54bf94]::ty::PseudoCanonicalInput<rustc_middle[927fbe768a54bf94]::mir::interpret::GlobalId>)>>::call_once
  27:     0x7f5d4a261408 - rustc_query_system[d2dd35691c1a46d5]::query::plumbing::try_execute_query::<rustc_query_impl[5c216bf84e04a0c]::DynamicConfig<rustc_query_system[d2dd35691c1a46d5]::query::caches::DefaultCache<rustc_middle[927fbe768a54bf94]::ty::PseudoCanonicalInput<rustc_middle[927fbe768a54bf94]::mir::interpret::GlobalId>, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[5c216bf84e04a0c]::plumbing::QueryCtxt, false>
  28:     0x7f5d4a261030 - rustc_query_impl[5c216bf84e04a0c]::query_impl::eval_to_valtree::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f5d4689b50a - <rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>::const_eval_resolve_for_typeck
  30:     0x7f5d499e4b56 - rustc_trait_selection[3fae8a94a2769d0d]::traits::try_evaluate_const
  31:     0x7f5d499d90fe - <rustc_trait_selection[3fae8a94a2769d0d]::traits::query::normalize::QueryNormalizer as rustc_type_ir[125e7728d77fb71d]::fold::FallibleTypeFolder<rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>>::try_fold_const
  32:     0x7f5d499d6108 - <rustc_traits[d83a550a31027e56]::normalize_erasing_regions::provide::{closure#0} as core[9b0602b26cbac703]::ops::function::FnOnce<(rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt, rustc_middle[927fbe768a54bf94]::ty::PseudoCanonicalInput<rustc_middle[927fbe768a54bf94]::ty::generic_args::GenericArg>)>>::call_once
  33:     0x7f5d499d54e0 - rustc_query_impl[5c216bf84e04a0c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5c216bf84e04a0c]::query_impl::try_normalize_generic_arg_after_erasing_regions::dynamic_query::{closure#2}::{closure#0}, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 8usize]>>
  34:     0x7f5d499d470d - rustc_query_system[d2dd35691c1a46d5]::query::plumbing::try_execute_query::<rustc_query_impl[5c216bf84e04a0c]::DynamicConfig<rustc_query_system[d2dd35691c1a46d5]::query::caches::DefaultCache<rustc_middle[927fbe768a54bf94]::ty::PseudoCanonicalInput<rustc_middle[927fbe768a54bf94]::ty::generic_args::GenericArg>, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[5c216bf84e04a0c]::plumbing::QueryCtxt, false>
  35:     0x7f5d499d43d8 - rustc_query_impl[5c216bf84e04a0c]::query_impl::try_normalize_generic_arg_after_erasing_regions::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f5d4aa748c8 - <rustc_middle[927fbe768a54bf94]::ty::normalize_erasing_regions::TryNormalizeAfterErasingRegionsFolder as rustc_type_ir[125e7728d77fb71d]::fold::FallibleTypeFolder<rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>>::try_fold_const
  37:     0x7f5d47a722dc - <rustc_hir_typeck[6bc7108e6ab36b3f]::writeback::EagerlyNormalizeConsts as rustc_type_ir[125e7728d77fb71d]::fold::TypeFolder<rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>>::fold_const
  38:     0x7f5d484d014f - <rustc_middle[927fbe768a54bf94]::ty::generic_args::GenericArg as rustc_type_ir[125e7728d77fb71d]::fold::TypeFoldable<rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>>::fold_with::<rustc_hir_typeck[6bc7108e6ab36b3f]::writeback::EagerlyNormalizeConsts>
  39:     0x7f5d484d2f76 - <&rustc_middle[927fbe768a54bf94]::ty::list::RawList<(), rustc_middle[927fbe768a54bf94]::ty::generic_args::GenericArg> as rustc_type_ir[125e7728d77fb71d]::fold::TypeFoldable<rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>>::fold_with::<rustc_hir_typeck[6bc7108e6ab36b3f]::writeback::EagerlyNormalizeConsts>
  40:     0x7f5d478ad7c6 - <rustc_middle[927fbe768a54bf94]::ty::Ty as rustc_type_ir[125e7728d77fb71d]::fold::TypeSuperFoldable<rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>>::super_fold_with::<rustc_hir_typeck[6bc7108e6ab36b3f]::writeback::EagerlyNormalizeConsts>
  41:     0x7f5d49bee7bf - <rustc_hir_typeck[6bc7108e6ab36b3f]::writeback::WritebackCx>::visit_node_id
  42:     0x7f5d4a52126a - <rustc_hir_typeck[6bc7108e6ab36b3f]::writeback::WritebackCx as rustc_hir[7fe254796a2591e6]::intravisit::Visitor>::visit_expr
  43:     0x7f5d4a526f65 - <rustc_hir_typeck[6bc7108e6ab36b3f]::fn_ctxt::FnCtxt>::resolve_type_vars_in_body
  44:     0x7f5d4a53d006 - rustc_hir_typeck[6bc7108e6ab36b3f]::typeck_with_inspect::{closure#0}
  45:     0x7f5d4a539674 - rustc_query_impl[5c216bf84e04a0c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5c216bf84e04a0c]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 8usize]>>
  46:     0x7f5d49a29a77 - rustc_query_system[d2dd35691c1a46d5]::query::plumbing::try_execute_query::<rustc_query_impl[5c216bf84e04a0c]::DynamicConfig<rustc_data_structures[e0806a14897e55a9]::vec_cache::VecCache<rustc_span[581a14f343ce28cf]::def_id::LocalDefId, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[d2dd35691c1a46d5]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[5c216bf84e04a0c]::plumbing::QueryCtxt, false>
  47:     0x7f5d49a29349 - rustc_query_impl[5c216bf84e04a0c]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  48:     0x7f5d4a271bf3 - <rustc_middle[927fbe768a54bf94]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[5c94152ec3a3a6a4]::check_crate::{closure#2}>::{closure#0}
  49:     0x7f5d4a271604 - rustc_hir_analysis[5c94152ec3a3a6a4]::check_crate
  50:     0x7f5d49a23bdb - rustc_interface[7ff7c1edf762f4c3]::passes::analysis
  51:     0x7f5d49a23827 - rustc_query_impl[5c216bf84e04a0c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5c216bf84e04a0c]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 0usize]>>
  52:     0x7f5d4a98cca6 - rustc_query_system[d2dd35691c1a46d5]::query::plumbing::try_execute_query::<rustc_query_impl[5c216bf84e04a0c]::DynamicConfig<rustc_query_system[d2dd35691c1a46d5]::query::caches::SingleCache<rustc_middle[927fbe768a54bf94]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[5c216bf84e04a0c]::plumbing::QueryCtxt, false>
  53:     0x7f5d4a98c876 - rustc_query_impl[5c216bf84e04a0c]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  54:     0x7f5d4ab52314 - <rustc_interface[7ff7c1edf762f4c3]::passes::create_and_enter_global_ctxt<core[9b0602b26cbac703]::option::Option<rustc_interface[7ff7c1edf762f4c3]::queries::Linker>, rustc_driver_impl[cb5a0d29d79f9b0b]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[9b0602b26cbac703]::ops::function::FnOnce<(&rustc_session[91ba16556b88832]::session::Session, rustc_middle[927fbe768a54bf94]::ty::context::CurrentGcx, alloc[be64b5636c6ea185]::sync::Arc<rustc_data_structures[e0806a14897e55a9]::jobserver::Proxy>, &std[4ef27b15e8c8b39f]::sync::once_lock::OnceLock<rustc_middle[927fbe768a54bf94]::ty::context::GlobalCtxt>, &rustc_data_structures[e0806a14897e55a9]::sync::worker_local::WorkerLocal<rustc_middle[927fbe768a54bf94]::arena::Arena>, &rustc_data_structures[e0806a14897e55a9]::sync::worker_local::WorkerLocal<rustc_hir[7fe254796a2591e6]::Arena>, rustc_driver_impl[cb5a0d29d79f9b0b]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  55:     0x7f5d4aa01918 - rustc_interface[7ff7c1edf762f4c3]::interface::run_compiler::<(), rustc_driver_impl[cb5a0d29d79f9b0b]::run_compiler::{closure#0}>::{closure#1}
  56:     0x7f5d4a90a88e - std[4ef27b15e8c8b39f]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[7ff7c1edf762f4c3]::util::run_in_thread_with_globals<rustc_interface[7ff7c1edf762f4c3]::util::run_in_thread_pool_with_globals<rustc_interface[7ff7c1edf762f4c3]::interface::run_compiler<(), rustc_driver_impl[cb5a0d29d79f9b0b]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  57:     0x7f5d4a90a660 - <std[4ef27b15e8c8b39f]::thread::lifecycle::spawn_unchecked<rustc_interface[7ff7c1edf762f4c3]::util::run_in_thread_with_globals<rustc_interface[7ff7c1edf762f4c3]::util::run_in_thread_pool_with_globals<rustc_interface[7ff7c1edf762f4c3]::interface::run_compiler<(), rustc_driver_impl[cb5a0d29d79f9b0b]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[9b0602b26cbac703]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  58:     0x7f5d4a90cd38 - <std[4ef27b15e8c8b39f]::sys::thread::unix::Thread>::new::thread_start
  59:     0x7f5d4429698b - <unknown>
  60:     0x7f5d4431a9cc - <unknown>
  61:                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 1.94.0-nightly (08f833aa1 2026-01-11) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [valtree_to_const_val] converting type-level constant value to MIR constant value
#1 [eval_to_allocation_raw] const-evaluating + checking `pass_enum::{constant#0}`
#2 [eval_to_valtree] evaluating type-level constant
#3 [try_normalize_generic_arg_after_erasing_regions] normalizing `const {N}`
#4 [typeck] type-checking `pass_enum`
#5 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 4 previous errors; 2 warnings emitted

Some errors have detailed explanations: E0107, E0601.
For more information about an error, try `rustc --explain E0107`.

@rustbot label +F-generic_const_exprs +F-min_generic_const_args

[Delta17920]

@rustbot claim