ICE: `failed to normalize const, but it is not generic: UnevaluatedConst`

[matthiaskrgr]

auto-reduced (treereduce-rust):

//@compile-flags: -Zincremental-verify-ich=yes -Cincremental=<dir> -Cdebuginfo=2 -Clink-dead-code=true -Zvalidate-mir --edition=2024
trait Q {
    const ASSOC: usize;
}

impl<'a, W: ?Sized> Q for [u8; N] {}

pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] {
    todo!()
}

original:

#![crate_type = "lib"]

trait Q {
    const ASSOC: usize;
}

impl<'a, W: ?Sized> Q for [u8; N] {
    //~^ ERROR: the constant `N` is not of type `usize`
    const ASSOC: usize = 1;
}

pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] {
    //~^ ERROR: the constant `13` is not of type `u64`
    todo!()
}

Version information

rustc 1.87.0-nightly (ed49386d3 2025-02-19)
binary: rustc
commit-hash: ed49386d3aa3a445a9889707fd405df01723eced
commit-date: 2025-02-19
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Possibly related line of code:

rust/compiler/rustc_ty_utils/src/layout.rs

Lines 146 to 158 in ed49386

	ct: ty::Const<'tcx>,
	) -> Result<ty::Value<'tcx>, &'tcx LayoutError<'tcx>> {
	match ct.kind() {
	ty::ConstKind::Value(cv) => Ok(cv),
	ty::ConstKind::Param(_) | ty::ConstKind::Expr(_) | ty::ConstKind::Unevaluated(_) => {
	if !ct.has_param() {
	bug!("failed to normalize const, but it is not generic: {ct:?}");
	}
	Err(error(cx, LayoutError::TooGeneric(ty)))
	}
	ty::ConstKind::Infer(_)
	| ty::ConstKind::Bound(..)
	| ty::ConstKind::Placeholder(_)

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zincremental-verify-ich=yes -Cincremental=<dir> -Cdebuginfo=2 -Clink-dead-code=true -Zvalidate-mir --edition=2024

Program output

error[E0425]: cannot find value `N` in this scope
 --> /tmp/icemaker_global_tempdir.MNIZNQo6CYeL/rustc_testrunner_tmpdir_reporting.Qq5ognT5KM0J/mvce.rs:5:32
  |
5 | impl<'a, W: ?Sized> Q for [u8; N] {}
  |                                ^ not found in this scope

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.MNIZNQo6CYeL/rustc_testrunner_tmpdir_reporting.Qq5ognT5KM0J/mvce.rs:9:2
  |
9 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.MNIZNQo6CYeL/rustc_testrunner_tmpdir_reporting.Qq5ognT5KM0J/mvce.rs`

error[E0207]: the type parameter `W` is not constrained by the impl trait, self type, or predicates
 --> /tmp/icemaker_global_tempdir.MNIZNQo6CYeL/rustc_testrunner_tmpdir_reporting.Qq5ognT5KM0J/mvce.rs:5:10
  |
5 | impl<'a, W: ?Sized> Q for [u8; N] {}
  |          ^ unconstrained type parameter

error: internal compiler error: compiler/rustc_ty_utils/src/layout.rs:152:17: failed to normalize const, but it is not generic: UnevaluatedConst { def: DefId(0:10 ~ mvce[846c]::test::{constant#0}), args: [] }


thread 'rustc' panicked at compiler/rustc_ty_utils/src/layout.rs:152:17:
Box<dyn Any>
stack backtrace:
   0:     0x7d3ff999a8e4 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h8474fc63c522d8ef
   1:     0x7d3ffa21a2ac - core::fmt::write::h807495cdc673c9ad
   2:     0x7d3ffb18d291 - std::io::Write::write_fmt::ha095d9f81ce0ab0f
   3:     0x7d3ff999a742 - std::sys::backtrace::BacktraceLock::print::h6697e7571ddb1a7a
   4:     0x7d3ff999cf4e - std::panicking::default_hook::{{closure}}::h809b6cc791b58376
   5:     0x7d3ff999cb24 - std::panicking::default_hook::h552e31dd2ff71c94
   6:     0x7d3ff8ae8d17 - std[751aac3a1d4a21ec]::panicking::update_hook::<alloc[e70108a9cb6abf43]::boxed::Box<rustc_driver_impl[2db46e11a3788224]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7d3ff999d7c3 - std::panicking::rust_panic_with_hook::h31b9a9fc06967d1a
   8:     0x7d3ff8b24bb1 - std[751aac3a1d4a21ec]::panicking::begin_panic::<rustc_errors[a11b7d5dcf14c424]::ExplicitBug>::{closure#0}
   9:     0x7d3ff8b18fc6 - std[751aac3a1d4a21ec]::sys::backtrace::__rust_end_short_backtrace::<std[751aac3a1d4a21ec]::panicking::begin_panic<rustc_errors[a11b7d5dcf14c424]::ExplicitBug>::{closure#0}, !>
  10:     0x7d3ff8b18da7 - std[751aac3a1d4a21ec]::panicking::begin_panic::<rustc_errors[a11b7d5dcf14c424]::ExplicitBug>
  11:     0x7d3ff8b2e531 - <rustc_errors[a11b7d5dcf14c424]::diagnostic::BugAbort as rustc_errors[a11b7d5dcf14c424]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x7d3ff90feb06 - rustc_middle[cad254c74eefe1b7]::util::bug::opt_span_bug_fmt::<rustc_span[3242d24a3aa68a91]::span_encoding::Span>::{closure#0}
  13:     0x7d3ff90e7d7a - rustc_middle[cad254c74eefe1b7]::ty::context::tls::with_opt::<rustc_middle[cad254c74eefe1b7]::util::bug::opt_span_bug_fmt<rustc_span[3242d24a3aa68a91]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7d3ff90e7c0b - rustc_middle[cad254c74eefe1b7]::ty::context::tls::with_context_opt::<rustc_middle[cad254c74eefe1b7]::ty::context::tls::with_opt<rustc_middle[cad254c74eefe1b7]::util::bug::opt_span_bug_fmt<rustc_span[3242d24a3aa68a91]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7d3ff7784de0 - rustc_middle[cad254c74eefe1b7]::util::bug::bug_fmt
  16:     0x7d3ffa7e6469 - rustc_ty_utils[5f7f94c7724baf90]::layout::layout_of_uncached
  17:     0x7d3ffa7d3d24 - rustc_ty_utils[5f7f94c7724baf90]::layout::layout_of
  18:     0x7d3ffa7d3c88 - rustc_query_impl[db8619f7f72bce84]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[db8619f7f72bce84]::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 16usize]>>
  19:     0x7d3ffa7bf84d - rustc_query_system[61afea02fdc7dc5c]::query::plumbing::try_execute_query::<rustc_query_impl[db8619f7f72bce84]::DynamicConfig<rustc_query_system[61afea02fdc7dc5c]::query::caches::DefaultCache<rustc_middle[cad254c74eefe1b7]::ty::PseudoCanonicalInput<rustc_middle[cad254c74eefe1b7]::ty::Ty>, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 16usize]>>, false, true, false>, rustc_query_impl[db8619f7f72bce84]::plumbing::QueryCtxt, true>
  20:     0x7d3ffa7be452 - rustc_query_impl[db8619f7f72bce84]::query_impl::layout_of::get_query_incr::__rust_end_short_backtrace
  21:     0x7d3ffb0c80f0 - <rustc_mir_transform[5f9d0e5befb1dd62]::known_panics_lint::KnownPanicsLint as rustc_mir_transform[5f9d0e5befb1dd62]::pass_manager::MirLint>::run_lint
  22:     0x7d3ffa20979b - rustc_mir_transform[5f9d0e5befb1dd62]::run_analysis_to_runtime_passes
  23:     0x7d3ffa5cf2d9 - rustc_mir_transform[5f9d0e5befb1dd62]::mir_drops_elaborated_and_const_checked
  24:     0x7d3ffa5cef1f - rustc_query_impl[db8619f7f72bce84]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[db8619f7f72bce84]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 8usize]>>
  25:     0x7d3ffa5c6d17 - rustc_query_system[61afea02fdc7dc5c]::query::plumbing::try_execute_query::<rustc_query_impl[db8619f7f72bce84]::DynamicConfig<rustc_data_structures[7f723801f239d808]::vec_cache::VecCache<rustc_span[3242d24a3aa68a91]::def_id::LocalDefId, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[61afea02fdc7dc5c]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[db8619f7f72bce84]::plumbing::QueryCtxt, true>
  26:     0x7d3ffa6b0e21 - rustc_query_impl[db8619f7f72bce84]::query_impl::mir_drops_elaborated_and_const_checked::get_query_incr::__rust_end_short_backtrace
  27:     0x7d3ffa5cc3e2 - rustc_interface[8d7befe99ce7adde]::passes::run_required_analyses
  28:     0x7d3ffb18923a - rustc_interface[8d7befe99ce7adde]::passes::analysis
  29:     0x7d3ffb189219 - rustc_query_impl[db8619f7f72bce84]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[db8619f7f72bce84]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 0usize]>>
  30:     0x7d3ffb184b19 - rustc_query_system[61afea02fdc7dc5c]::query::plumbing::try_execute_query::<rustc_query_impl[db8619f7f72bce84]::DynamicConfig<rustc_query_system[61afea02fdc7dc5c]::query::caches::SingleCache<rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[db8619f7f72bce84]::plumbing::QueryCtxt, true>
  31:     0x7d3ffb184522 - rustc_query_impl[db8619f7f72bce84]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  32:     0x7d3ffb248f3c - rustc_interface[8d7befe99ce7adde]::passes::create_and_enter_global_ctxt::<core[5038f2ec8886dbab]::option::Option<rustc_interface[8d7befe99ce7adde]::queries::Linker>, rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  33:     0x7d3ffb23c8ab - rustc_interface[8d7befe99ce7adde]::interface::run_compiler::<(), rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}>::{closure#1}
  34:     0x7d3ffb102dc8 - std[751aac3a1d4a21ec]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_with_globals<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_pool_with_globals<rustc_interface[8d7befe99ce7adde]::interface::run_compiler<(), rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  35:     0x7d3ffb1031f4 - <<std[751aac3a1d4a21ec]::thread::Builder>::spawn_unchecked_<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_with_globals<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_pool_with_globals<rustc_interface[8d7befe99ce7adde]::interface::run_compiler<(), rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[5038f2ec8886dbab]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  36:     0x7d3ffb103baf - std::sys::pal::unix::thread::Thread::new::thread_start::ha52e702df20ec6b5
  37:     0x7d3ff529470a - <unknown>
  38:     0x7d3ff5318aac - <unknown>
  39:                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: rustc 1.87.0-nightly (ed49386d3 2025-02-19) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z incremental-verify-ich=yes -C incremental=[REDACTED] -C debuginfo=2 -C link-dead-code=true -Z validate-mir

query stack during panic:
#0 [layout_of] computing layout of `[u8; <[u8; 13] as Q>::ASSOC]`
#1 [mir_drops_elaborated_and_const_checked] elaborating drops for `test`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 4 previous errors

Some errors have detailed explanations: E0207, E0425, E0601.
For more information about an error, try `rustc --explain E0207`.

[matthiaskrgr]

#![crate_type="lib"]
trait A {
    const B: usize;
}
impl<C: ?Sized> A for [u8; D] {}
fn e() -> [u8; <[u8; 3]>::B] {
    todo!()
}

[lukas-code]

Caused by 7a667d2, looks like that bug needs to be delayed.