ICE `const array must have an array type`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(min_generic_const_args)]

trait Trait<const N: usize> {}

fn foo<T>()
where
    T: Trait<{ [] }>,
{
}

fn main() {}

original:

//@ check-pass

#![feature(min_generic_const_args)]
#![expect(incomplete_features)]

trait Trait<const N: usize> {}

fn foo<T>()
where
    T: Trait<{ [] }>
{}

fn main() {}

Version information

rustc 1.94.0-nightly (aefa10405 2026-01-12)
binary: rustc
commit-hash: aefa10405d7b67b3780027484cb02c85d3a3bf36
commit-date: 2026-01-12
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 `min_generic_const_args` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.XoItPpf41vJQ/rustc_testrunner_tmpdir_reporting.YhURTGNvE5dq/mvce.rs:1:12
  |
1 | #![feature(min_generic_const_args)]
  |            ^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #132980 <https://github.com/rust-lang/rust/issues/132980> for more information
  = note: `#[warn(incomplete_features)]` on by default

warning: trait `Trait` is never used
 --> /tmp/icemaker_global_tempdir.XoItPpf41vJQ/rustc_testrunner_tmpdir_reporting.YhURTGNvE5dq/mvce.rs:3:7
  |
3 | trait Trait<const N: usize> {}
  |       ^^^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: function `foo` is never used
 --> /tmp/icemaker_global_tempdir.XoItPpf41vJQ/rustc_testrunner_tmpdir_reporting.YhURTGNvE5dq/mvce.rs:5:4
  |
5 | fn foo<T>()
  |    ^^^

warning: 3 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: const array must have an array type
 --> /tmp/icemaker_global_tempdir.XoItPpf41vJQ/rustc_testrunner_tmpdir_reporting.YhURTGNvE5dq/mvce.rs:7:16
  |
7 |     T: Trait<{ [] }>,
  |                ^^
  |
note: delayed at /rustc-dev/aefa10405d7b67b3780027484cb02c85d3a3bf36/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs:2418:20
         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: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_const_arg
         5: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_generic_args_of_path::{closure#0}
         6: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_poly_trait_ref
         7: rustc_hir_analysis::collect::predicates_of::gather_explicit_predicates_of::{closure#0}
         8: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::explicit_predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
         9: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        10: rustc_query_impl::query_impl::explicit_predicates_of::get_query_non_incr::__rust_end_short_backtrace
        11: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
        12: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        13: rustc_query_impl::query_impl::predicates_of::get_query_non_incr::__rust_end_short_backtrace
        14: rustc_hir_analysis::check::check::check_item_type
        15: rustc_hir_analysis::check::wfcheck::check_well_formed
        16: 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]>>
        17: 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>
        18: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
        19: rustc_hir_analysis::check::wfcheck::check_type_wf
        20: 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]>>
        21: 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>
        22: rustc_query_impl::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
        23: rustc_hir_analysis::check_crate
        24: rustc_interface::passes::analysis
        25: 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]>>
        26: 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>
        27: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        28: <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}
        29: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        30: 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}, ()>
        31: <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}
        32: <std::sys::thread::unix::Thread>::new::thread_start
        33: <unknown>
        34: <unknown>
      
 --> /tmp/icemaker_global_tempdir.XoItPpf41vJQ/rustc_testrunner_tmpdir_reporting.YhURTGNvE5dq/mvce.rs:7:16
  |
7 |     T: Trait<{ [] }>,
  |                ^^

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 (aefa10405 2026-01-12) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

@rustbot label +F-min_generic_const_args