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ICE cannot find `!BoundConst { var: 1 }` in param-env: ParamEnv { }

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C-bug F-with_negative_coherence I-ICE S-bug-has-test S-has-mcve T-compiler
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Rust
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Description

auto-reduced (treereduce-rust):

#![feature(with_negative_coherence)]
trait ExampleTrait {
    type AssociatedType;
}

impl<T, const N: usize> ExampleTrait for [T; N]
{
    
}

pub struct Happy<T> {
    ,
}

impl<T> ExampleTrait for Happy<T>

{
    
}




impl<T, const MYSIZE: usize> ExampleTrait for Happy<T>
where
    [T; MYSIZE]: ,
    <[T; MYSIZE] as T>::AssociatedType: Clone,
    [T; N]: , // 💣
    <[T; MYSIZE] as ExampleTrait>::AssociatedType: Clone,
{
    
}

original:

trait ExampleTrait {
    type AssociatedType;
}

impl<T, const N: usize> ExampleTrait for [T; N]
{
    type AssociatedType = T;
}

pub struct Happy<T> {
    arr: [Happy; MYSIZE],
}

impl<T> ExampleTrait for Happy<T>
where
    [T; 10]: ExampleTrait,
    <[T; 10] as ExampleTrait>::AssociatedType: Clone,
    [T; 10]: ExampleTrait,
    <[T; 10] as ExampleTrait>::AssociatedType: Clone,
{
    type AssociatedType = T;
}

pub const MYSIZE: usize = 10;
pub struct Sad<T> {
    arr: [T; MYSIZE],
}

impl<T, const MYSIZE: usize> ExampleTrait for Happy<T>
where
    [T; MYSIZE]: ExampleTrait,
    <[T; MYSIZE] as T>::AssociatedType: Clone,
    [T; N]: ExampleTrait, // 💣
    <[T; MYSIZE] as ExampleTrait>::AssociatedType: Clone,
{
    type AssociatedType = T;
}

Version information

rustc 1.93.0-nightly (c90bcb957 2025-11-06)
binary: rustc
commit-hash: c90bcb9571b7aab0d8beaa2ce8a998ffaf079d38
commit-date: 2025-11-06
host: x86_64-unknown-linux-gnu
release: 1.93.0-nightly
LLVM version: 21.1.3

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zcrate-attr=feature(with_negative_coherence)

Program output 

error: expected identifier, found `,`
  --> /tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs:11:5
   |
10 | pub struct Happy<T> {
   |            ----- while parsing this struct
11 |     ,
   |     ^ expected identifier

error[E0404]: expected trait, found type parameter `T`
  --> /tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs:26:21
   |
23 | impl<T, const MYSIZE: usize> ExampleTrait for Happy<T>
   |      - found this type parameter
...
26 |     <[T; MYSIZE] as T>::AssociatedType: Clone,
   |                     ^ not a trait

error[E0425]: cannot find value `N` in this scope
  --> /tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs:27:9
   |
27 |     [T; N]: , // 💣
   |         ^ not found in this scope

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs:31:2
   |
31 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs`


thread 'rustc' (1257200) panicked at /rustc-dev/c90bcb9571b7aab0d8beaa2ce8a998ffaf079d38/compiler/rustc_type_ir/src/inherent.rs:580:13:
cannot find `!BoundConst { var: 1 }` in param-env: ParamEnv {
    caller_bounds: [
        Binder { value: TraitPredicate(<!0 as std::marker::Sized>, polarity:Positive), bound_vars: [] },
    ],
}
stack backtrace:
   0:     0x7f8944a5f223 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hde21067283f7e82e
   1:     0x7f8945201afc - core::fmt::write::h24186904251c31cb
   2:     0x7f8944a13d93 - std::io::Write::write_fmt::h3ab9f1f4d8d19b72
   3:     0x7f8944a253a2 - std::sys::backtrace::BacktraceLock::print::he038489aba5894a6
   4:     0x7f8944a2b3f9 - std::panicking::default_hook::{{closure}}::h80a26d916c49679b
   5:     0x7f8944a2af23 - std::panicking::default_hook::he2e9efee79b3dce9
   6:     0x7f8943a20c91 - std[e95ebcffb71a5621]::panicking::update_hook::<alloc[6ba2be5df7d20276]::boxed::Box<rustc_driver_impl[8bc3447375e6b2d8]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7f8944a2b81f - std::panicking::panic_with_hook::hf5648b7cec6bc73e
   8:     0x7f8944a2b5da - std::panicking::panic_handler::{{closure}}::h1b2ed3864ba94359
   9:     0x7f8944a254e9 - std::sys::backtrace::__rust_end_short_backtrace::hd0186b2b27f5aaa7
  10:     0x7f8944a060dd - __rustc[f7dae8b92efe1d7a]::rust_begin_unwind
  11:     0x7f8941a72000 - core::panicking::panic_fmt::hb5d6b83773432920
  12:     0x7f8945dab661 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate> as rustc_type_ir[5e1db4e3d840b3d9]::search_graph::Delegate>::compute_goal::{closure#0}
  13:     0x7f8945dc1257 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::evaluate_goal_raw
  14:     0x7f8945db13bc - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::try_evaluate_added_goals
  15:     0x7f8945f58750 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::evaluate_added_goals_and_make_canonical_response
  16:     0x7f8945da60fb - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::assemble_impl_candidates::<rustc_type_ir[5e1db4e3d840b3d9]::predicate::TraitPredicate<rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::{closure#0}
  17:     0x7f8945da17e6 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::compute_trait_goal
  18:     0x7f8945daadff - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate> as rustc_type_ir[5e1db4e3d840b3d9]::search_graph::Delegate>::compute_goal::{closure#0}
  19:     0x7f8945dc1257 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::evaluate_goal_raw
  20:     0x7f8945db176d - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::try_evaluate_added_goals
  21:     0x7f8945daa4f1 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate> as rustc_type_ir[5e1db4e3d840b3d9]::search_graph::Delegate>::compute_goal::{closure#0}
  22:     0x7f8945dc1257 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::evaluate_goal_raw
  23:     0x7f8945db13bc - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::try_evaluate_added_goals
  24:     0x7f8945da2b7c - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::compute_trait_goal
  25:     0x7f8945daa04b - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate> as rustc_type_ir[5e1db4e3d840b3d9]::search_graph::Delegate>::compute_goal::{closure#0}
  26:     0x7f8945dc1257 - <rustc_next_trait_solver[80d5b8e7e915485e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[47719877e32dbd7c]::solve::delegate::SolverDelegate, rustc_middle[9ce76f953d15e2f6]::ty::context::TyCtxt>>::evaluate_goal_raw
  27:     0x7f8945db69c3 - <rustc_trait_selection[47719877e32dbd7c]::solve::fulfill::FulfillmentCtxt<rustc_infer[35191db886fd87e]::traits::engine::ScrubbedTraitError> as rustc_infer[35191db886fd87e]::traits::engine::TraitEngine<rustc_infer[35191db886fd87e]::traits::engine::ScrubbedTraitError>>::evaluate_obligations_error_on_ambiguity
  28:     0x7f8944883e1e - rustc_trait_selection[47719877e32dbd7c]::traits::coherence::impl_intersection_has_negative_obligation
  29:     0x7f8945dbeb0c - rustc_trait_selection[47719877e32dbd7c]::traits::coherence::overlap
  30:     0x7f8941f51e62 - <rustc_middle[9ce76f953d15e2f6]::traits::specialization_graph::Children as rustc_trait_selection[47719877e32dbd7c]::traits::specialize::specialization_graph::ChildrenExt>::insert
  31:     0x7f8945306e88 - <rustc_middle[9ce76f953d15e2f6]::traits::specialization_graph::Graph as rustc_trait_selection[47719877e32dbd7c]::traits::specialize::specialization_graph::GraphExt>::insert
  32:     0x7f8945308368 - rustc_trait_selection[47719877e32dbd7c]::traits::specialize::specialization_graph_provider
  33:     0x7f8945307d8d - rustc_query_impl[8ae232d5147ca84e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8ae232d5147ca84e]::query_impl::specialization_graph_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 8usize]>>
  34:     0x7f894521c806 - rustc_query_system[41b9c06994168e52]::query::plumbing::try_execute_query::<rustc_query_impl[8ae232d5147ca84e]::DynamicConfig<rustc_query_system[41b9c06994168e52]::query::caches::DefIdCache<rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[8ae232d5147ca84e]::plumbing::QueryCtxt, false>
  35:     0x7f89459d1337 - rustc_query_impl[8ae232d5147ca84e]::query_impl::specialization_graph_of::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f89459d1690 - rustc_hir_analysis[5cd9912eb92b8e51]::coherence::coherent_trait
  37:     0x7f89459d135f - rustc_query_impl[8ae232d5147ca84e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8ae232d5147ca84e]::query_impl::coherent_trait::dynamic_query::{closure#2}::{closure#0}, rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 1usize]>>
  38:     0x7f8945a3c523 - rustc_query_system[41b9c06994168e52]::query::plumbing::try_execute_query::<rustc_query_impl[8ae232d5147ca84e]::DynamicConfig<rustc_query_system[41b9c06994168e52]::query::caches::DefIdCache<rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[8ae232d5147ca84e]::plumbing::QueryCtxt, false>
  39:     0x7f8945a3b5a4 - rustc_query_impl[8ae232d5147ca84e]::query_impl::coherent_trait::get_query_non_incr::__rust_end_short_backtrace
  40:     0x7f89459de2fb - rustc_hir_analysis[5cd9912eb92b8e51]::check::check::check_item_type
  41:     0x7f89459db39c - rustc_hir_analysis[5cd9912eb92b8e51]::check::wfcheck::check_well_formed
  42:     0x7f89459db375 - rustc_query_impl[8ae232d5147ca84e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8ae232d5147ca84e]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 1usize]>>
  43:     0x7f89459dabec - rustc_query_system[41b9c06994168e52]::query::plumbing::try_execute_query::<rustc_query_impl[8ae232d5147ca84e]::DynamicConfig<rustc_data_structures[de67cf687b97999a]::vec_cache::VecCache<rustc_span[28eed06c8d001cb1]::def_id::LocalDefId, rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[41b9c06994168e52]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[8ae232d5147ca84e]::plumbing::QueryCtxt, false>
  44:     0x7f89459da702 - rustc_query_impl[8ae232d5147ca84e]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  45:     0x7f89459d7c70 - rustc_hir_analysis[5cd9912eb92b8e51]::check::wfcheck::check_type_wf
  46:     0x7f89459d7b5d - rustc_query_impl[8ae232d5147ca84e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8ae232d5147ca84e]::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 1usize]>>
  47:     0x7f8946296948 - rustc_query_system[41b9c06994168e52]::query::plumbing::try_execute_query::<rustc_query_impl[8ae232d5147ca84e]::DynamicConfig<rustc_query_system[41b9c06994168e52]::query::caches::SingleCache<rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[8ae232d5147ca84e]::plumbing::QueryCtxt, false>
  48:     0x7f894629670e - rustc_query_impl[8ae232d5147ca84e]::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
  49:     0x7f894553acba - rustc_hir_analysis[5cd9912eb92b8e51]::check_crate
  50:     0x7f8945521ab0 - rustc_interface[d5ff205a9ab97820]::passes::analysis
  51:     0x7f8945521773 - rustc_query_impl[8ae232d5147ca84e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8ae232d5147ca84e]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 0usize]>>
  52:     0x7f894629d360 - rustc_query_system[41b9c06994168e52]::query::plumbing::try_execute_query::<rustc_query_impl[8ae232d5147ca84e]::DynamicConfig<rustc_query_system[41b9c06994168e52]::query::caches::SingleCache<rustc_middle[9ce76f953d15e2f6]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[8ae232d5147ca84e]::plumbing::QueryCtxt, false>
  53:     0x7f894629cfb6 - rustc_query_impl[8ae232d5147ca84e]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  54:     0x7f894655a00a - <rustc_interface[d5ff205a9ab97820]::passes::create_and_enter_global_ctxt<core[a4c7c2348b0f0abe]::option::Option<rustc_interface[d5ff205a9ab97820]::queries::Linker>, rustc_driver_impl[8bc3447375e6b2d8]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[a4c7c2348b0f0abe]::ops::function::FnOnce<(&rustc_session[84c9ddeb8f325268]::session::Session, rustc_middle[9ce76f953d15e2f6]::ty::context::CurrentGcx, alloc[6ba2be5df7d20276]::sync::Arc<rustc_data_structures[de67cf687b97999a]::jobserver::Proxy>, &std[e95ebcffb71a5621]::sync::once_lock::OnceLock<rustc_middle[9ce76f953d15e2f6]::ty::context::GlobalCtxt>, &rustc_data_structures[de67cf687b97999a]::sync::worker_local::WorkerLocal<rustc_middle[9ce76f953d15e2f6]::arena::Arena>, &rustc_data_structures[de67cf687b97999a]::sync::worker_local::WorkerLocal<rustc_hir[1534e3459f232f80]::Arena>, rustc_driver_impl[8bc3447375e6b2d8]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  55:     0x7f89463fbfe9 - rustc_interface[d5ff205a9ab97820]::interface::run_compiler::<(), rustc_driver_impl[8bc3447375e6b2d8]::run_compiler::{closure#0}>::{closure#1}
  56:     0x7f8946090e3c - std[e95ebcffb71a5621]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[d5ff205a9ab97820]::util::run_in_thread_with_globals<rustc_interface[d5ff205a9ab97820]::util::run_in_thread_pool_with_globals<rustc_interface[d5ff205a9ab97820]::interface::run_compiler<(), rustc_driver_impl[8bc3447375e6b2d8]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  57:     0x7f8946090b20 - <<std[e95ebcffb71a5621]::thread::Builder>::spawn_unchecked_<rustc_interface[d5ff205a9ab97820]::util::run_in_thread_with_globals<rustc_interface[d5ff205a9ab97820]::util::run_in_thread_pool_with_globals<rustc_interface[d5ff205a9ab97820]::interface::run_compiler<(), rustc_driver_impl[8bc3447375e6b2d8]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[a4c7c2348b0f0abe]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  58:     0x7f8946095daf - std::sys::thread::unix::Thread::new::thread_start::hb3dc6483caa1b987
  59:     0x7f893fa969cb - <unknown>
  60:     0x7f893fb1aa0c - <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 1.93.0-nightly (c90bcb957 2025-11-06) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z crate-attr=feature(with_negative_coherence) -Z dump-mir-dir=dir

query stack during panic:
#0 [specialization_graph_of] building specialization graph of trait `ExampleTrait`
#1 [coherent_trait] coherence checking all impls of trait `ExampleTrait`
#2 [check_well_formed] checking that `<impl at /tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs:5:1: 5:48>` is well-formed
#3 [check_type_wf] checking that types are well-formed
#4 [analysis] running analysis passes on crate `mvce`
end of query stack
error[E0392]: type parameter `T` is never used
  --> /tmp/icemaker_global_tempdir.zD8pQUt7PVI8/rustc_testrunner_tmpdir_reporting.UI4hL7vNdrSM/mvce.rs:10:18
   |
10 | pub struct Happy<T> {
   |                  ^ unused type parameter
   |
   = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
   = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead

error: aborting due to 5 previous errors

Some errors have detailed explanations: E0392, E0404, E0425, E0601.
For more information about an error, try `rustc --explain E0392`.

@rustbot label +F-with_negative_coherence

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the reduced reproducer with the reported rustc command and confirm the ICE. Then read compiler/rustc_type_ir/src/inherent.rs around line 580 and trace the reported rustc_next_trait_solver, coherence overlap, and specialization_graph entries. Done means the reproducer no longer panics and produces an appropriate compiler result.

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
Quiet
Clarity
Mostly clear
Newbie friendliness
35/100

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