ICE: `index out of bounds` in `rustc_middle/src/ty/g... | rust-lang/rust

Nobody has claimed this yet.

Code

#![feature(generic_const_exprs)]
#![allow(incomplete_features)]

struct Test<const N: usize>;

fn new<const N: usize>() -> Test<N>
where
    [(); N * 1]: Sized,
{
    Test
}

fn test<const N: usize>() -> Test<{ N - 1 }>
where
    [(); (N - usize::MAX) * 1]: Sized,
{
    new()
}

fn main() {}

A mutant of glacier2's fixed/134479-2.rs.

Error output

command: rustc

thread 'rustc' (44328524) panicked at compiler/rustc_middle/src/ty/generic_args.rs:54:14:
index out of bounds: the len is 0 but the index is 0

Backtrace

thread 'rustc' (44328524) panicked at compiler/rustc_middle/src/ty/generic_args.rs:54:14:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic_bounds_check
   3: <rustc_trait_selection::traits::wf::WfPredicates>::add_wf_preds_for_inherent_projection
   4: <rustc_trait_selection::traits::wf::WfPredicates as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_const
   5: <rustc_trait_selection::traits::wf::WfPredicates as rustc_type_ir::visit::TypeVisitor<rustc_middle::ty::context::TyCtxt>>::visit_const
   6: rustc_trait_selection::traits::wf::obligations
   7: <rustc_trait_selection::traits::fulfill::FulfillProcessor as rustc_data_structures::obligation_forest::ObligationProcessor>::process_obligation
   8: <rustc_data_structures::obligation_forest::ObligationForest<rustc_trait_selection::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection::traits::fulfill::FulfillProcessor>
   9: <rustc_trait_selection::traits::fulfill::FulfillmentContext<rustc_trait_selection::traits::FulfillmentError> as rustc_infer::traits::engine::TraitEngine<rustc_trait_selection::traits::FulfillmentError>>::try_evaluate_obligations
  10: <rustc_hir_typeck::fn_ctxt::FnCtxt>::resolve_vars_with_obligations::<rustc_middle::ty::Ty>
  11: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  12: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_kind
  13: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  14: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_block
  15: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  16: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_return_or_body_tail
  17: rustc_hir_typeck::check::check_fn
  18: rustc_hir_typeck::typeck_with_inspect::{closure#0}
  19: rustc_hir_typeck::typeck
      [... omitted 1 frame ...]
  20: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}
  21: rustc_hir_analysis::check_crate
  22: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  23: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  24: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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: please attach the file at `/Volumes/T7/workspace/run_251022_250515_genie_full/scratch/rustc-ice-2025-10-24T06_24_19-73644.txt` to your bug report

query stack during panic:
#0 [typeck] type-checking `test`
#1 [analysis] running analysis passes on this crate
end of query stack

Notes

ICE location: rustc_middle/src/ty/generic_args.rs Line-54
https://github.com/rust-lang/rust/blob/6501e64fcb02d22b49d6e59d10a7692ec8095619/compiler/rustc_middle/src/ty/generic_args.rs#L43-L55
I searched for open ICE issues with generic_args.rs query, and I guess there's no duplicates in there. (https://github.com/rust-lang/rust/issues?q=is%3Aissue%20state%3Aopen%20label%3AI-ICE%20%22generic_args.rs%22)

@rustbot label +F-generic_const_exprs

Start by reproducing the ICE with the provided generic_const_exprs example on the reported nightly compiler. Read compiler/rustc_middle/src/ty/generic_args.rs around type_at and follow the backtrace through add_wf_preds_for_inherent_projection and rustc_hir_typeck. Done means the example no longer causes an index-out-of-bounds panic.

Written by the indexing model from the issue text.

ICE: `index out of bounds` in `rustc_middle/src/ty/generic_args.rs`'s `type_at`

Description

Code

Meta

Error output

Notes

Contributor guide

First steps

Research direction

Assessment

ICE: `index out of bounds` in `rustc_middle/src/ty/generic_args.rs`'s `type_at`

Description

Code

Meta

Error output

Notes

Contributor guide

First steps

Research direction

Assessment

Get new issues in your inbox