rust-lang / rust-lang/rust

ICE `DefId does not have a "const_of_item"`

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-Zvalidate-mir C-bug F-min_generic_const_args I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

auto-reduced (treereduce-rust):

//@compile-flags: -Zincremental-verify-ich=yes -Cincremental=<dir> -Cdebuginfo=2 -Clink-dead-code=true -Zvalidate-mir -Zquery-dep-graph -Zthreads=4 --edition=2024
#![feature(min_generic_const_args)]

pub trait Foo {}
impl Foo for [u8; std::path::MAIN_SEPARATOR] {}

original:

// regression test for #133808.

#![allow(dead_code)]
#![feature(min_generic_const_args)]
#![allow(incomplete_features)]
#![crate_type = "lib"]

pub trait Foo {}
impl Foo for [u8; std::path::MAIN_SEPARATOR] {}
//~^ ERROR the constant `MAIN_SEPARATOR` is not of type `usize`

Version information

rustc 1.93.0-nightly (acda5e9f9 2025-11-09)
binary: rustc
commit-hash: acda5e9f9aadac705b851935b14aa3d34a67d428
commit-date: 2025-11-09
host: x86_64-unknown-linux-gnu
release: 1.93.0-nightly
LLVM version: 21.1.3

Possibly related line of code:
https://github.com/rust-lang/rust/blob/acda5e9f9aadac705b851935b14aa3d34a67d428/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs#L218-L230

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zincremental-verify-ich=yes -Cincremental=<dir> -Cdebuginfo=2 -Clink-dead-code=true -Zvalidate-mir -Zquery-dep-graph -Zthreads=4 --edition=2024

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.lw7Ljes8uH6W/rustc_testrunner_tmpdir_reporting.Iw1HM8tcwzkj/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

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.lw7Ljes8uH6W/rustc_testrunner_tmpdir_reporting.Iw1HM8tcwzkj/mvce.rs:4:48
  |
4 | impl Foo for [u8; std::path::MAIN_SEPARATOR] {}
  |                                                ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.lw7Ljes8uH6W/rustc_testrunner_tmpdir_reporting.Iw1HM8tcwzkj/mvce.rs`


thread 'rustc' (2141391) panicked at compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs:224:1:
DefId(1:5606 ~ std[b4c0]::path::MAIN_SEPARATOR) does not have a "const_of_item"
stack backtrace:
   0:     0x7ffaa066c9c3 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h0dc93c2810c40bd0
   1:     0x7ffaa0e01afc - core::fmt::write::hacdaf2bbd154e9b5
   2:     0x7ffaa0621533 - std::io::Write::write_fmt::h75e948926e9dfbe3
   3:     0x7ffaa0632b42 - std::sys::backtrace::BacktraceLock::print::h251013828edeee18
   4:     0x7ffaa0638b99 - std::panicking::default_hook::{{closure}}::hf6c9462acd913055
   5:     0x7ffaa06386c3 - std::panicking::default_hook::h4c9fd5029d2f8b73
   6:     0x7ffa9f62a721 - std[b4c06921f787550c]::panicking::update_hook::<alloc[7ed4a9fe7ec582b8]::boxed::Box<rustc_driver_impl[87c4f5c8377f9862]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7ffaa0638fbf - std::panicking::panic_with_hook::h02a757165762df79
   8:     0x7ffaa0638d7a - std::panicking::panic_handler::{{closure}}::h66210c1b0223aa50
   9:     0x7ffaa0632c79 - std::sys::backtrace::__rust_end_short_backtrace::h24c6c4da1001b922
  10:     0x7ffaa061387d - __rustc[90cdb7b664da1e1e]::rust_begin_unwind
  11:     0x7ffa9d6ba730 - core::panicking::panic_fmt::hb5559fbca70a856c
  12:     0x7ffa9fbbc1a2 - rustc_metadata[cb4a4348587efc7]::rmeta::decoder::cstore_impl::provide_extern::const_of_item::{closure#2}
  13:     0x7ffa9fbc7f6c - rustc_metadata[cb4a4348587efc7]::rmeta::decoder::cstore_impl::provide_extern::const_of_item
  14:     0x7ffaa000b78b - rustc_query_impl[d4db0883806fa552]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d4db0883806fa552]::query_impl::const_of_item::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1e1513fa521466b3]::query::erase::Erased<[u8; 8usize]>>
  15:     0x7ffaa12687c1 - rustc_query_system[d03d33f2f2d15895]::query::plumbing::try_execute_query::<rustc_query_impl[d4db0883806fa552]::DynamicConfig<rustc_query_system[d03d33f2f2d15895]::query::caches::DefIdCache<rustc_middle[1e1513fa521466b3]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[d4db0883806fa552]::plumbing::QueryCtxt, true>
  16:     0x7ffaa00a56b7 - rustc_query_impl[d4db0883806fa552]::query_impl::const_of_item::get_query_incr::__rust_end_short_backtrace
  17:     0x7ffaa226cbdd - <rustc_trait_selection[bb82b8f413fd2a2a]::traits::normalize::AssocTypeNormalizer>::normalize_free_alias::{closure#0}
  18:     0x7ffaa10215aa - <rustc_trait_selection[bb82b8f413fd2a2a]::traits::normalize::AssocTypeNormalizer as rustc_type_ir[a0e454d4d0a700c1]::fold::TypeFolder<rustc_middle[1e1513fa521466b3]::ty::context::TyCtxt>>::fold_const
  19:     0x7ffaa1023bd7 - <rustc_middle[1e1513fa521466b3]::ty::Ty as rustc_type_ir[a0e454d4d0a700c1]::fold::TypeSuperFoldable<rustc_middle[1e1513fa521466b3]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[bb82b8f413fd2a2a]::traits::normalize::AssocTypeNormalizer>
  20:     0x7ffaa14878c4 - <&rustc_middle[1e1513fa521466b3]::ty::list::RawList<(), rustc_middle[1e1513fa521466b3]::ty::generic_args::GenericArg> as rustc_type_ir[a0e454d4d0a700c1]::fold::TypeFoldable<rustc_middle[1e1513fa521466b3]::ty::context::TyCtxt>>::fold_with::<rustc_trait_selection[bb82b8f413fd2a2a]::traits::normalize::AssocTypeNormalizer>
  21:     0x7ffaa170f603 - rustc_trait_selection[bb82b8f413fd2a2a]::traits::normalize::normalize_with_depth_to::<rustc_type_ir[a0e454d4d0a700c1]::predicate::TraitRef<rustc_middle[1e1513fa521466b3]::ty::context::TyCtxt>>::{closure#0}
  22:     0x7ffaa17101b1 - rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_impl
  23:     0x7ffaa160ef37 - rustc_hir_analysis[3bbcf63e422e422d]::check::check::check_item_type
  24:     0x7ffaa160c41c - rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_well_formed
  25:     0x7ffaa160c3f5 - rustc_query_impl[d4db0883806fa552]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d4db0883806fa552]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1e1513fa521466b3]::query::erase::Erased<[u8; 1usize]>>
  26:     0x7ffaa0f05c21 - rustc_query_system[d03d33f2f2d15895]::query::plumbing::try_execute_query::<rustc_query_impl[d4db0883806fa552]::DynamicConfig<rustc_data_structures[aff1d8a073485c2a]::vec_cache::VecCache<rustc_span[39972e28049286de]::def_id::LocalDefId, rustc_middle[1e1513fa521466b3]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[d03d33f2f2d15895]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[d4db0883806fa552]::plumbing::QueryCtxt, true>
  27:     0x7ffaa0f03f6d - rustc_query_impl[d4db0883806fa552]::query_impl::check_well_formed::get_query_incr::__rust_end_short_backtrace
  28:     0x7ffa9f75682b - rustc_middle[1e1513fa521466b3]::query::inner::query_ensure_error_guaranteed::<rustc_data_structures[aff1d8a073485c2a]::vec_cache::VecCache<rustc_span[39972e28049286de]::def_id::LocalDefId, rustc_middle[1e1513fa521466b3]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[d03d33f2f2d15895]::dep_graph::graph::DepNodeIndex>, ()>
  29:     0x7ffa9f76727e - rustc_data_structures[aff1d8a073485c2a]::sync::parallel::par_slice::par_rec::<&rustc_hir[2565f01ea710f611]::hir::ItemId, rustc_data_structures[aff1d8a073485c2a]::sync::parallel::try_par_for_each_in<&[rustc_hir[2565f01ea710f611]::hir::ItemId], rustc_span[39972e28049286de]::ErrorGuaranteed, <rustc_middle[1e1513fa521466b3]::hir::ModuleItems>::par_items<rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>
  30:     0x7ffa9f7a0644 - rustc_thread_pool[80e8a9b643659d2e]::join::join_context::<rustc_thread_pool[80e8a9b643659d2e]::join::join::call<(), rustc_data_structures[aff1d8a073485c2a]::sync::parallel::par_slice::par_rec<&rustc_hir[2565f01ea710f611]::hir::ItemId, rustc_data_structures[aff1d8a073485c2a]::sync::parallel::try_par_for_each_in<&[rustc_hir[2565f01ea710f611]::hir::ItemId], rustc_span[39972e28049286de]::ErrorGuaranteed, <rustc_middle[1e1513fa521466b3]::hir::ModuleItems>::par_items<rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}>::{closure#0}, rustc_thread_pool[80e8a9b643659d2e]::join::join::call<(), rustc_data_structures[aff1d8a073485c2a]::sync::parallel::par_slice::par_rec<&rustc_hir[2565f01ea710f611]::hir::ItemId, rustc_data_structures[aff1d8a073485c2a]::sync::parallel::try_par_for_each_in<&[rustc_hir[2565f01ea710f611]::hir::ItemId], rustc_span[39972e28049286de]::ErrorGuaranteed, <rustc_middle[1e1513fa521466b3]::hir::ModuleItems>::par_items<rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#2}>::{closure#0}, (), ()>::{closure#0}
  31:     0x7ffa9f767325 - rustc_data_structures[aff1d8a073485c2a]::sync::parallel::par_slice::par_rec::<&rustc_hir[2565f01ea710f611]::hir::ItemId, rustc_data_structures[aff1d8a073485c2a]::sync::parallel::try_par_for_each_in<&[rustc_hir[2565f01ea710f611]::hir::ItemId], rustc_span[39972e28049286de]::ErrorGuaranteed, <rustc_middle[1e1513fa521466b3]::hir::ModuleItems>::par_items<rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>
  32:     0x7ffa9f829b37 - <rustc_thread_pool[80e8a9b643659d2e]::job::StackJob<rustc_thread_pool[80e8a9b643659d2e]::latch::SpinLatch, rustc_thread_pool[80e8a9b643659d2e]::join::join_context<rustc_thread_pool[80e8a9b643659d2e]::join::join::call<(), rustc_data_structures[aff1d8a073485c2a]::sync::parallel::par_slice::par_rec<&rustc_hir[2565f01ea710f611]::hir::ItemId, rustc_data_structures[aff1d8a073485c2a]::sync::parallel::try_par_for_each_in<&[rustc_hir[2565f01ea710f611]::hir::ItemId], rustc_span[39972e28049286de]::ErrorGuaranteed, <rustc_middle[1e1513fa521466b3]::hir::ModuleItems>::par_items<rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}>::{closure#0}, rustc_thread_pool[80e8a9b643659d2e]::join::join::call<(), rustc_data_structures[aff1d8a073485c2a]::sync::parallel::par_slice::par_rec<&rustc_hir[2565f01ea710f611]::hir::ItemId, rustc_data_structures[aff1d8a073485c2a]::sync::parallel::try_par_for_each_in<&[rustc_hir[2565f01ea710f611]::hir::ItemId], rustc_span[39972e28049286de]::ErrorGuaranteed, <rustc_middle[1e1513fa521466b3]::hir::ModuleItems>::par_items<rustc_hir_analysis[3bbcf63e422e422d]::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#2}>::{closure#0}, (), ()>::{closure#0}::{closure#0}, ()> as rustc_thread_pool[80e8a9b643659d2e]::job::Job>::execute
  33:     0x7ffaa034362f - <rustc_thread_pool[80e8a9b643659d2e]::registry::WorkerThread>::wait_or_steal_until_cold
  34:     0x7ffaa03420d1 - <rustc_thread_pool[80e8a9b643659d2e]::registry::ThreadBuilder>::run
  35:     0x7ffa9f62284d - std[b4c06921f787550c]::sys::backtrace::__rust_begin_short_backtrace::<<rustc_thread_pool[80e8a9b643659d2e]::ThreadPoolBuilder>::build_scoped<rustc_interface[df9ddd9c9467ef8b]::util::run_in_thread_pool_with_globals<rustc_interface[df9ddd9c9467ef8b]::interface::run_compiler<(), rustc_driver_impl[87c4f5c8377f9862]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#0}, rustc_interface[df9ddd9c9467ef8b]::util::run_in_thread_pool_with_globals<rustc_interface[df9ddd9c9467ef8b]::interface::run_compiler<(), rustc_driver_impl[87c4f5c8377f9862]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
  36:     0x7ffa9f62dd52 - <<std[b4c06921f787550c]::thread::Builder>::spawn_unchecked_<<rustc_thread_pool[80e8a9b643659d2e]::ThreadPoolBuilder>::build_scoped<rustc_interface[df9ddd9c9467ef8b]::util::run_in_thread_pool_with_globals<rustc_interface[df9ddd9c9467ef8b]::interface::run_compiler<(), rustc_driver_impl[87c4f5c8377f9862]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#0}, rustc_interface[df9ddd9c9467ef8b]::util::run_in_thread_pool_with_globals<rustc_interface[df9ddd9c9467ef8b]::interface::run_compiler<(), rustc_driver_impl[87c4f5c8377f9862]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>::{closure#1} as core[f1f7c8de62d6692e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  37:     0x7ffaa1c8afef - std::sys::thread::unix::Thread::new::thread_start::h6ee5f4a2e2de181d
  38:     0x7ffa9b6969cb - <unknown>
  39:     0x7ffa9b71aa0c - <unknown>
  40:                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 (acda5e9f9 2025-11-09) 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 -Z query-dep-graph -Z threads=4

query stack during panic:
#0 [const_of_item] computing the type-level value for `std::path::MAIN_SEPARATOR`
#1 [check_well_formed] checking that `<impl at /tmp/icemaker_global_tempdir.lw7Ljes8uH6W/rustc_testrunner_tmpdir_reporting.Iw1HM8tcwzkj/mvce.rs:4:1: 4:45>` is well-formed
#2 [check_type_wf] checking that types are well-formed
#3 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 1 previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0601`.

@rustbot label +F-min_generic_const_args +-Zvalidate-mir

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 with the minimized reproducer and its compiler flags, then inspect compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs around the reported const_of_item code. Reproduce the ICE with rustc and trace how std::path::MAIN_SEPARATOR reaches that query. Done means the reproducer no longer panics while retaining the expected compiler diagnostic.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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