ICE: `ty::ConstKind::Error constructed but no error reported`

[matthiaskrgr]

original:

#![feature(
    generic_const_items,
    min_generic_const_args,
    generic_const_parameter_types,
    unsized_const_params
)]
use std::marker::ConstParamTy_;
struct Foo<T> {
    field: T,
}
#[type_const]
const WRAP<T : ConstParamTy_> : T = {
      Foo::<T>{field : 1}
    };
fn main() {}

Version information

rustc 1.94.0-nightly (b68e16cfc 2026-01-11)
binary: rustc
commit-hash: b68e16cfc0e9f8b29c9ec41bfa6ab0a637eff19c
commit-date: 2026-01-11
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8

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

Program output

warning: the feature `generic_const_items` is incomplete and may not be safe to use and/or cause compiler crashes
 --> code.rs:2:5
  |
2 |     generic_const_items,
  |     ^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #113521 <https://github.com/rust-lang/rust/issues/113521> 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
 --> code.rs:3:5
  |
3 |     min_generic_const_args,
  |     ^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #132980 <https://github.com/rust-lang/rust/issues/132980> for more information

warning: the feature `generic_const_parameter_types` is incomplete and may not be safe to use and/or cause compiler crashes
 --> code.rs:4:5
  |
4 |     generic_const_parameter_types,
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #137626 <https://github.com/rust-lang/rust/issues/137626> for more information

warning: the feature `unsized_const_params` is incomplete and may not be safe to use and/or cause compiler crashes
 --> code.rs:5:5
  |
5 |     unsized_const_params
  |     ^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #95174 <https://github.com/rust-lang/rust/issues/95174> for more information

warning: struct `Foo` is never constructed
 --> code.rs:8:8
  |
8 | struct Foo<T> {
  |        ^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: constant `WRAP` is never used
  --> code.rs:12:7
   |
12 | const WRAP<T : ConstParamTy_> : T = {
   |       ^^^^

warning: 6 warnings emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: ty::ConstKind::Error constructed but no error reported
  |
  = note: delayed at /rustc-dev/b68e16cfc0e9f8b29c9ec41bfa6ab0a637eff19c/compiler/rustc_mir_build/src/thir/constant.rs:90:21
             0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
             1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
             2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
             3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, &str>
             4: <rustc_middle::ty::consts::Const>::new_misc_error
             5: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::lit_to_const::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
             6: <rustc_query_impl::query_impl::lit_to_const::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_middle::mir::interpret::LitToConstInput)>>::call_once
             7: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::mir::interpret::LitToConstInput, rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
             8: rustc_query_impl::query_impl::lit_to_const::get_query_non_incr::__rust_end_short_backtrace
             9: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_const_arg
            10: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_const_arg
            11: rustc_hir_analysis::collect::const_of_item
            12: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::const_of_item::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
            13: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            14: rustc_query_impl::query_impl::const_of_item::get_query_non_incr::__rust_end_short_backtrace
            15: rustc_hir_analysis::check::wfcheck::check_type_const
            16: rustc_hir_analysis::check::check::check_item_type
            17: rustc_hir_analysis::check::wfcheck::check_well_formed
            18: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
            19: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            20: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
            21: rustc_hir_analysis::check::wfcheck::check_type_wf
            22: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
            23: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            24: rustc_query_impl::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
            25: rustc_hir_analysis::check_crate
            26: rustc_interface::passes::analysis
            27: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
            28: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            29: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
            30: <rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
            31: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
            32: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
            33: <std::thread::lifecycle::spawn_unchecked<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
            34: <std::sys::thread::unix::Thread>::new::thread_start
            35: <unknown>
            36: <unknown>


error: internal compiler error: failed to report fulfillment errors
  |
  = note: delayed at /rustc-dev/b68e16cfc0e9f8b29c9ec41bfa6ab0a637eff19c/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs:286:47
             0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
             1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
             2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
             3: <rustc_errors::DiagCtxtHandle>::delayed_bug::<&str>
             4: <rustc_trait_selection::error_reporting::TypeErrCtxt>::report_fulfillment_errors
             5: rustc_hir_analysis::check::check::check_item_type
             6: rustc_hir_analysis::check::wfcheck::check_well_formed
             7: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
             8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
             9: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
            10: rustc_hir_analysis::check::wfcheck::check_type_wf
            11: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
            12: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            13: rustc_query_impl::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
            14: rustc_hir_analysis::check_crate
            15: rustc_interface::passes::analysis
            16: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
            17: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            18: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
            19: <rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
            20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
            21: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
            22: <std::thread::lifecycle::spawn_unchecked<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
            23: <std::sys::thread::unix::Thread>::new::thread_start
            24: <unknown>
            25: <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 `/home/matthias/vcs/github/CRED/rustc-ice-2026-01-11T23_33_03-360561.txt` to your bug report

note: rustc 1.94.0-nightly (b68e16cfc 2026-01-11) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[dianne]

Like #151625, I expect this is because <dyn HirTyLowerer>::lower_const_arg_literal doesn't do any error handling. It uses lit_to_const, which returns a const error when the literal doesn't match its expected type, but doesn't report the error itself; it instead creates a delayed bug. Nothing downstream can do much about it either once there's already an error in the const.