rust-lang / rust-lang/rust

ICE: cannot find `N/#0` in param-env

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C-bug F-adt_const_params F-generic_const_parameter_types I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

It is very similar to #143117, but it seems to manifest differently. I'm not sure if this is the same issue.

Code
#![feature(adt_const_params, generic_const_parameter_types)]
#![expect(incomplete_features)]
#[derive(PartialEq)]
struct Inner<const N: usize>([u8; N]);
struct Outer<const N: usize, const M: Inner<N>>(Inner<N>);

fn main() {}
Meta

rustc --version --verbose:

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
Program Output 

error: internal compiler error: /rustc-dev/b68e16cfc0e9f8b29c9ec41bfa6ab0a637eff19c/compiler/rustc_middle/src/ty/sty.rs:374:13: cannot find `N/#0` in param-env: ParamEnv {
                                    caller_bounds: [],
                                }


thread 'rustc' (3) panicked at /rustc-dev/b68e16cfc0e9f8b29c9ec41bfa6ab0a637eff19c/compiler/rustc_middle/src/ty/sty.rs:374:13:
Box<dyn Any>
stack backtrace:
   0:     0x7f6762a40763 - <<std[dc78c416db172f4a]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[ae121572cd1b547a]::fmt::Display>::fmt
   1:     0x7f676300e308 - core[ae121572cd1b547a]::fmt::write
   2:     0x7f6762a57156 - <std[dc78c416db172f4a]::sys::stdio::unix::Stderr as std[dc78c416db172f4a]::io::Write>::write_fmt
   3:     0x7f6762a167d8 - std[dc78c416db172f4a]::panicking::default_hook::{closure#0}
   4:     0x7f6762a33e93 - std[dc78c416db172f4a]::panicking::default_hook
   5:     0x7f6761a17aba - std[dc78c416db172f4a]::panicking::update_hook::<alloc[abf3b1e21d0b7705]::boxed::Box<rustc_driver_impl[f421dd94c081429e]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f6762a34172 - std[dc78c416db172f4a]::panicking::panic_with_hook
   7:     0x7f6761a54e91 - std[dc78c416db172f4a]::panicking::begin_panic::<rustc_errors[7f188bff54032bff]::ExplicitBug>::{closure#0}
   8:     0x7f6761a454f6 - std[dc78c416db172f4a]::sys::backtrace::__rust_end_short_backtrace::<std[dc78c416db172f4a]::panicking::begin_panic<rustc_errors[7f188bff54032bff]::ExplicitBug>::{closure#0}, !>
   9:     0x7f6761a4512f - std[dc78c416db172f4a]::panicking::begin_panic::<rustc_errors[7f188bff54032bff]::ExplicitBug>
  10:     0x7f6761a72b91 - <rustc_errors[7f188bff54032bff]::diagnostic::BugAbort as rustc_errors[7f188bff54032bff]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7f6762023e69 - rustc_middle[dceae28993ab1a32]::util::bug::opt_span_bug_fmt::<rustc_span[bdd546435e4bce71]::span_encoding::Span>::{closure#0}
  12:     0x7f6762023ff2 - rustc_middle[dceae28993ab1a32]::ty::context::tls::with_opt::<rustc_middle[dceae28993ab1a32]::util::bug::opt_span_bug_fmt<rustc_span[bdd546435e4bce71]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7f676201561b - rustc_middle[dceae28993ab1a32]::ty::context::tls::with_context_opt::<rustc_middle[dceae28993ab1a32]::ty::context::tls::with_opt<rustc_middle[dceae28993ab1a32]::util::bug::opt_span_bug_fmt<rustc_span[bdd546435e4bce71]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7f675f9cfe04 - rustc_middle[dceae28993ab1a32]::util::bug::bug_fmt
  15:     0x7f676377fc50 - <rustc_trait_selection[677722ff3ec175c6]::traits::fulfill::FulfillProcessor as rustc_data_structures[94c88a1c28c3c4cc]::obligation_forest::ObligationProcessor>::process_obligation
  16:     0x7f67630046e4 - <rustc_data_structures[94c88a1c28c3c4cc]::obligation_forest::ObligationForest<rustc_trait_selection[677722ff3ec175c6]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[677722ff3ec175c6]::traits::fulfill::FulfillProcessor>
  17:     0x7f6763002bdf - <rustc_trait_selection[677722ff3ec175c6]::traits::fulfill::FulfillmentContext<rustc_infer[306238161a7f0bc9]::traits::engine::ScrubbedTraitError> as rustc_infer[306238161a7f0bc9]::traits::engine::TraitEngine<rustc_infer[306238161a7f0bc9]::traits::engine::ScrubbedTraitError>>::evaluate_obligations_error_on_ambiguity
  18:     0x7f67645c98b5 - rustc_ty_utils[a0c51cdc47e3de8]::structural_match::has_structural_eq_impl
  19:     0x7f67645c942b - rustc_query_impl[94cb984c31ae0c8e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[94cb984c31ae0c8e]::query_impl::has_structural_eq_impl::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 1usize]>>
  20:     0x7f67645c8efa - rustc_query_system[6a3016a52e4c2c98]::query::plumbing::try_execute_query::<rustc_query_impl[94cb984c31ae0c8e]::DynamicConfig<rustc_query_system[6a3016a52e4c2c98]::query::caches::DefaultCache<rustc_middle[dceae28993ab1a32]::ty::Ty, rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[94cb984c31ae0c8e]::plumbing::QueryCtxt, false>
  21:     0x7f67645c8c52 - rustc_query_impl[94cb984c31ae0c8e]::query_impl::has_structural_eq_impl::get_query_non_incr::__rust_end_short_backtrace
  22:     0x7f67628102df - <rustc_trait_selection[677722ff3ec175c6]::error_reporting::TypeErrCtxt>::report_selection_error
  23:     0x7f676134520e - <rustc_trait_selection[677722ff3ec175c6]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  24:     0x7f67636dfe17 - rustc_hir_analysis[4469fe91bd5f7a5]::check::wfcheck::check_well_formed
  25:     0x7f67636df7d7 - rustc_query_impl[94cb984c31ae0c8e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[94cb984c31ae0c8e]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 1usize]>>
  26:     0x7f67636df04d - rustc_query_system[6a3016a52e4c2c98]::query::plumbing::try_execute_query::<rustc_query_impl[94cb984c31ae0c8e]::DynamicConfig<rustc_data_structures[94c88a1c28c3c4cc]::vec_cache::VecCache<rustc_span[bdd546435e4bce71]::def_id::LocalDefId, rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[6a3016a52e4c2c98]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[94cb984c31ae0c8e]::plumbing::QueryCtxt, false>
  27:     0x7f67636deb56 - rustc_query_impl[94cb984c31ae0c8e]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7f67636dc2f0 - rustc_hir_analysis[4469fe91bd5f7a5]::check::wfcheck::check_type_wf
  29:     0x7f67636dc1dd - rustc_query_impl[94cb984c31ae0c8e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[94cb984c31ae0c8e]::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 1usize]>>
  30:     0x7f6764162848 - rustc_query_system[6a3016a52e4c2c98]::query::plumbing::try_execute_query::<rustc_query_impl[94cb984c31ae0c8e]::DynamicConfig<rustc_query_system[6a3016a52e4c2c98]::query::caches::SingleCache<rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[94cb984c31ae0c8e]::plumbing::QueryCtxt, false>
  31:     0x7f676416260e - rustc_query_impl[94cb984c31ae0c8e]::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
  32:     0x7f6763aec356 - rustc_hir_analysis[4469fe91bd5f7a5]::check_crate
  33:     0x7f676322519b - rustc_interface[fa71a63d738bff6a]::passes::analysis
  34:     0x7f6763224de7 - rustc_query_impl[94cb984c31ae0c8e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[94cb984c31ae0c8e]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 0usize]>>
  35:     0x7f6764164026 - rustc_query_system[6a3016a52e4c2c98]::query::plumbing::try_execute_query::<rustc_query_impl[94cb984c31ae0c8e]::DynamicConfig<rustc_query_system[6a3016a52e4c2c98]::query::caches::SingleCache<rustc_middle[dceae28993ab1a32]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[94cb984c31ae0c8e]::plumbing::QueryCtxt, false>
  36:     0x7f6764163d88 - rustc_query_impl[94cb984c31ae0c8e]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  37:     0x7f6764336254 - <rustc_interface[fa71a63d738bff6a]::passes::create_and_enter_global_ctxt<core[ae121572cd1b547a]::option::Option<rustc_interface[fa71a63d738bff6a]::queries::Linker>, rustc_driver_impl[f421dd94c081429e]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[ae121572cd1b547a]::ops::function::FnOnce<(&rustc_session[300e9a40ce91b12d]::session::Session, rustc_middle[dceae28993ab1a32]::ty::context::CurrentGcx, alloc[abf3b1e21d0b7705]::sync::Arc<rustc_data_structures[94c88a1c28c3c4cc]::jobserver::Proxy>, &std[dc78c416db172f4a]::sync::once_lock::OnceLock<rustc_middle[dceae28993ab1a32]::ty::context::GlobalCtxt>, &rustc_data_structures[94c88a1c28c3c4cc]::sync::worker_local::WorkerLocal<rustc_middle[dceae28993ab1a32]::arena::Arena>, &rustc_data_structures[94c88a1c28c3c4cc]::sync::worker_local::WorkerLocal<rustc_hir[8ab5b6b069b3d6b7]::Arena>, rustc_driver_impl[f421dd94c081429e]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  38:     0x7f67641ce118 - rustc_interface[fa71a63d738bff6a]::interface::run_compiler::<(), rustc_driver_impl[f421dd94c081429e]::run_compiler::{closure#0}>::{closure#1}
  39:     0x7f676404ec0e - std[dc78c416db172f4a]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[fa71a63d738bff6a]::util::run_in_thread_with_globals<rustc_interface[fa71a63d738bff6a]::util::run_in_thread_pool_with_globals<rustc_interface[fa71a63d738bff6a]::interface::run_compiler<(), rustc_driver_impl[f421dd94c081429e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  40:     0x7f676404e9e0 - <std[dc78c416db172f4a]::thread::lifecycle::spawn_unchecked<rustc_interface[fa71a63d738bff6a]::util::run_in_thread_with_globals<rustc_interface[fa71a63d738bff6a]::util::run_in_thread_pool_with_globals<rustc_interface[fa71a63d738bff6a]::interface::run_compiler<(), rustc_driver_impl[f421dd94c081429e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[ae121572cd1b547a]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x7f67640542b8 - <std[dc78c416db172f4a]::sys::thread::unix::Thread>::new::thread_start
  42:     0x7f675da94ac3 - <unknown>
  43:     0x7f675db268c0 - <unknown>
  44:                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 `/app/rustc-ice-2026-01-14T11_34_15-1.txt` to your bug report

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

note: compiler flags: -C debuginfo=2 --crate-type bin -C linker=/opt/compiler-explorer/gcc-15.2.0/bin/gcc

query stack during panic:
#0 [has_structural_eq_impl] computing whether `Inner<N>` implements `StructuralPartialEq`
#1 [check_well_formed] checking that `Outer` is well-formed
#2 [check_type_wf] checking that types are well-formed
#3 [analysis] running analysis passes on crate `example`
end of query stack
error: aborting due to 1 previous error

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Research direction

Reproduce the minimal example with the reported nightly compiler, then start at compiler/rustc_middle/src/ty/sty.rs:374 and follow the has_structural_eq_impl and check_well_formed query stack shown in the report. Done means the example no longer triggers an internal compiler error and the behavior is covered by an appropriate compiler regression test.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
30/100

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