ICE: "Missing value for constant, but no error reported?" with unresolvabe const due to trivial bounds

[FedericoBruzzone]

Code

playground

#![feature(trivial_bounds)]

trait Project {
    const ASSOC: usize;
}

fn foo()
where
    (): Project,
{
    [(); <() as Project>::ASSOC];
}

Rust Version

`rustc +nightly --version --verbose`:
rustc 1.86.0-nightly (99db2737c 2025-01-16)
binary: rustc
commit-hash: 99db2737c91d1e4b36b2ffc17dcda5878bcae625
commit-date: 2025-01-16
host: x86_64-unknown-linux-gnu
release: 1.86.0-nightly
LLVM version: 19.1.7

Current error output

error: internal compiler error: Missing value for constant, but no error reported?
  --> tests/ui/layout/uneval-const-rigid.rs:11:5
   |
11 |     [(); <() as Project>::ASSOC];
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: delayed at compiler/rustc_trait_selection/src/traits/const_evaluatable.rs:132:44 - disabled backtrace
  --> tests/ui/layout/uneval-const-rigid.rs:11:5
   |
11 |     [(); <() as Project>::ASSOC];
   |

Backtrace

error: internal compiler error: Missing value for constant, but no error reported?
  --> tmp.rs:11:5
   |
11 |     [(); <() as Project>::ASSOC];
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: delayed at compiler/rustc_trait_selection/src/traits/const_evaluatable.rs:132:44
         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_trait_selection::traits::const_evaluatable::is_const_evaluatable.cold
         5: <rustc_trait_selection::traits::fulfill::FulfillProcessor as rustc_data_structures::obligation_forest::ObligationProcessor>::process_obligation
         6: <rustc_data_structures::obligation_forest::ObligationForest<rustc_trait_selection::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection::traits::fulfill::FulfillProcessor>
         7: rustc_hir_typeck::typeck_with_fallback::{closure#0}
         8: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
         9: 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; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        10: rustc_query_impl::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
        11: <rustc_middle::hir::map::Map>::par_body_owners::<rustc_hir_analysis::check_crate::{closure#4}>::{closure#0}
        12: rustc_hir_analysis::check_crate
        13: rustc_interface::passes::run_required_analyses
        14: rustc_interface::passes::analysis
        15: 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]>>
        16: 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>
        17: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        18: 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}::{closure#0}
        19: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        20: 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}, ()>
        21: <<std::thread::Builder>::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}
        22: std::sys::pal::unix::thread::Thread::new::thread_start
        23: <unknown>
        24: <unknown>

Anything else?

This error was found during this PR, in the addition of TooGeneric as LayoutError.

Updates on this issue will be added later if found.

cc: @lukas-code

[theemathas]

Version that produces the ICE without unstable features:

trait Project {
    const ASSOC: usize;
}

fn foo()
where
    for<'a> (): Project,
{
    [(); <() as Project>::ASSOC];
}

[matthiaskrgr]

might be dupe of #135138

[FedericoBruzzone]

might be dupe of #135138

This is not actually a duplicated of #135138.
That ICE (#135138) will be fixed soon in this PR, but this ICE will remains.

[lukas-code]

This is unrelated to layout computation and happens because we always treat resolution errors in const eval as TooGeneric even if there are no generics:

rust/compiler/rustc_middle/src/mir/interpret/queries.rs

Line 84 in 73c0ae6

Ok(None) => Err(ErrorHandled::TooGeneric(DUMMY_SP)),

---

@theemathas FYI this for<'a> trick only sidesteps the feature gate for compatibility reasons and should not be considered stable behavior. All issues related to feature(trivial_bounds) can be reproduced without a feature gate by putting a binder in front of the trivial bounds.