[ICE]: infer: `index out of bounds: the len is 0 but the index is 0`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(supertrait_item_shadowing)]
#![feature(generic_const_exprs)]
trait E<'e> {
    type As;
}
trait F<'a>: E<'a> + for<'e> E<'e> {}

struct G<T>
where
    T: F<'e, As: E>,
{
    X: T,
}

original:

#![feature(supertrait_item_shadowing)]
#![feature(generic_const_exprs)]
trait E<'e> {
    type As;
}
trait F<'a>: E<'a> + for<'e> E<'e> {}

struct G<T>
where
    T: F<'e, As: E>,
{
    X: T,
}

fn main() {}

Version information

rustc 1.100.0-nightly (b0ca9c712 2026-08-22)
binary: rustc
commit-hash: b0ca9c712455d865c3bf0bf5325a3e79677a2d97
commit-date: 2026-08-22
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.0

Possibly related line of code:

rust/compiler/rustc_infer/src/infer/mod.rs

Lines 1498 to 1510 in b0ca9c7

	struct ToFreshVars<'tcx> {
	args: Vec<ty::GenericArg<'tcx>>,
	}
	impl<'tcx> BoundVarReplacerDelegate<'tcx> for ToFreshVars<'tcx> {
	fn replace_region(&mut self, br: ty::BoundRegion<'tcx>) -> ty::Region<'tcx> {
	self.args[br.var.index()].expect_region()
	}
	fn replace_ty(&mut self, bt: ty::BoundTy<'tcx>) -> Ty<'tcx> {
	self.args[bt.var.index()].expect_ty()
	}
	fn replace_const(&mut self, bc: ty::BoundConst<'tcx>) -> ty::Const<'tcx> {
	self.args[bc.var.index()].expect_const()

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error[E0261]: use of undeclared lifetime name `'e`
  --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:10:10
   |
10 |     T: F<'e, As: E>,
   |          ^^ undeclared lifetime
   |
   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
help: consider making the bound lifetime-generic with a new `'e` lifetime
   |
10 |     T: for<'e> F<'e, As: E>,
   |        +++++++
help: consider making the bound lifetime-generic with a new `'e` lifetime
   |
10 |     for<'e> T: F<'e, As: E>,
   |     +++++++
help: consider introducing lifetime `'e` here
   |
 8 | struct G<'e, T>
   |          +++

error[E0106]: missing lifetime specifier
  --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:10:18
   |
10 |     T: F<'e, As: E>,
   |                  ^ expected named lifetime parameter
   |
help: consider making the bound lifetime-generic with a new `'a` lifetime
   |
10 |     T: F<'e, As: for<'a> E<'a>>,
   |                  +++++++  ++++
help: consider making the bound lifetime-generic with a new `'a` lifetime
   |
10 |     T: for<'a> F<'e, As: E<'a>>,
   |        +++++++            ++++
help: consider making the bound lifetime-generic with a new `'a` lifetime
   |
10 |     for<'a> T: F<'e, As: E<'a>>,
   |     +++++++               ++++
help: consider introducing a named lifetime parameter
   |
 8 ~ struct G<'a, T>
 9 | where
10 ~     T: F<'e, As: E<'a>>,
   |

warning: `feature(generic_const_exprs)` is not supported with the next-generation trait solver
 --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:2:12
  |
2 | #![feature(generic_const_exprs)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: `-Znext-solver=globally` is currently enabled by default for testing
  = note: reverted the setting to `-Znext-solver=coherence` for this crate
  = note: the currently stable trait solver will be used for this crate
  = note: see issues #160895 <https://github.com/rust-lang/rust/issues/160895> for more information

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:2:12
  |
2 | #![feature(generic_const_exprs)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
  = note: `#[warn(incomplete_features)]` on by default

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:13:2
   |
13 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs`

error[E0283]: type annotations needed: cannot satisfy `Self: E<'a>`
 --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:6:14
  |
6 | trait F<'a>: E<'a> + for<'e> E<'e> {}
  |              ^^^^^
  |
note: multiple `impl`s or `where` clauses satisfying `Self: E<'a>` found
 --> /tmp/icemaker_global_tempdir.eqgShu82wjy8/rustc_testrunner_tmpdir_reporting.MZP3wCkwT6bQ/mvce.rs:6:14
  |
6 | trait F<'a>: E<'a> + for<'e> E<'e> {}
  |              ^^^^^   ^^^^^^^^^^^^^


thread 'rustc' (4014998) panicked at /rustc-dev/b0ca9c712455d865c3bf0bf5325a3e79677a2d97/compiler/rustc_infer/src/infer/mod.rs:1504:26:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0:     0x7f38f11fc246 - <<std[29541300fb290a5d]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[460910d47b72e8ee]::fmt::Display>::fmt
   1:     0x7f38f180b023 - core[460910d47b72e8ee]::fmt::write
   2:     0x7f38f121172c - <std[29541300fb290a5d]::sys::stdio::unix::Stderr as core[460910d47b72e8ee]::io::write::Write>::write_fmt
   3:     0x7f38f11cf61a - std[29541300fb290a5d]::panicking::default_hook::{closure#0}
   4:     0x7f38f11f04a3 - std[29541300fb290a5d]::panicking::default_hook
   5:     0x7f38f01a89aa - std[29541300fb290a5d]::panicking::update_hook::<alloc[e06df03e17637ff3]::boxed::Box<rustc_driver_impl[56abbf040ce8585c]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f38f11f0942 - std[29541300fb290a5d]::panicking::panic_with_hook
   7:     0x7f38f11cf6d2 - std[29541300fb290a5d]::panicking::panic_handler::{closure#0}
   8:     0x7f38f11c6509 - std[29541300fb290a5d]::sys::backtrace::__rust_end_short_backtrace::<std[29541300fb290a5d]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f38f11d100d - __rustc[764f694db36a77d7]::rust_begin_unwind
  10:     0x7f38edfaae3c - core[460910d47b72e8ee]::panicking::panic_fmt
  11:     0x7f38eea3647a - core[460910d47b72e8ee]::panicking::panic_bounds_check
  12:     0x7f38f396dccd - <<rustc_infer[775c003696668d9d]::infer::InferCtxt>::instantiate_binder_with_fresh_vars::ToFreshVars as rustc_middle[9d9ea3708d6e93f5]::ty::fold::BoundVarReplacerDelegate>::replace_region.cold
  13:     0x7f38f279374e - <&rustc_middle[9d9ea3708d6e93f5]::ty::list::RawList<(), rustc_middle[9d9ea3708d6e93f5]::ty::generic_args::GenericArg> as rustc_type_ir[c55ed8222f6694be]::fold::TypeFoldable<rustc_middle[9d9ea3708d6e93f5]::ty::context::TyCtxt>>::fold_with::<rustc_middle[9d9ea3708d6e93f5]::ty::fold::BoundVarReplacer<<rustc_infer[775c003696668d9d]::infer::InferCtxt>::instantiate_binder_with_fresh_vars::ToFreshVars>>
  14:     0x7f38f279467a - <rustc_middle[9d9ea3708d6e93f5]::ty::fold::BoundVarReplacer<<rustc_infer[775c003696668d9d]::infer::InferCtxt>::instantiate_binder_with_fresh_vars::ToFreshVars> as rustc_type_ir[c55ed8222f6694be]::fold::TypeFolder<rustc_middle[9d9ea3708d6e93f5]::ty::context::TyCtxt>>::fold_ty
  15:     0x7f38ed8c1db4 - <rustc_trait_selection[6d6a1773eb45fa07]::traits::select::SelectionContext>::candidate_from_obligation_no_cache
  16:     0x7f38f1d6ed27 - <rustc_trait_selection[6d6a1773eb45fa07]::traits::select::SelectionContext>::poly_select::{closure#0}
  17:     0x7f38f1d5b0b5 - rustc_trait_selection[6d6a1773eb45fa07]::traits::project::opt_normalize_projection_term
  18:     0x7f38f1d63355 - <rustc_trait_selection[6d6a1773eb45fa07]::traits::normalize::AssocTypeNormalizer as rustc_type_ir[c55ed8222f6694be]::fold::TypeFolder<rustc_middle[9d9ea3708d6e93f5]::ty::context::TyCtxt>>::fold_ty
  19:     0x7f38f1d61c93 - <&rustc_middle[9d9ea3708d6e93f5]::ty::list::RawList<(), rustc_middle[9d9ea3708d6e93f5]::ty::generic_args::GenericArg> as rustc_type_ir[c55ed8222f6694be]::fold::TypeFoldable<rustc_middle[9d9ea3708d6e93f5]::ty::context::TyCtxt>>::fold_with::<rustc_trait_selection[6d6a1773eb45fa07]::traits::normalize::AssocTypeNormalizer>
  20:     0x7f38f27c5d27 - <rustc_middle[9d9ea3708d6e93f5]::ty::predicate::Clause as rustc_type_ir[c55ed8222f6694be]::fold::TypeFoldable<rustc_middle[9d9ea3708d6e93f5]::ty::context::TyCtxt>>::fold_with::<rustc_trait_selection[6d6a1773eb45fa07]::traits::normalize::AssocTypeNormalizer>
  21:     0x7f38f27c527e - <rustc_infer[775c003696668d9d]::infer::at::At as rustc_trait_selection[6d6a1773eb45fa07]::traits::normalize::NormalizeExt>::normalize::<alloc[e06df03e17637ff3]::vec::Vec<rustc_middle[9d9ea3708d6e93f5]::ty::predicate::Clause>>
  22:     0x7f38f2d28322 - rustc_trait_selection[6d6a1773eb45fa07]::traits::do_normalize_clauses
  23:     0x7f38f1e536c0 - rustc_trait_selection[6d6a1773eb45fa07]::traits::normalize_param_env_or_error
  24:     0x7f38f1e5e8ea - rustc_ty_utils[a79d7b537cc149b5]::ty::param_env
  25:     0x7f38f186667d - rustc_query_impl[a298bd9aef25de82]::execution::try_execute_query::<rustc_middle[9d9ea3708d6e93f5]::query::caches::DefIdCache<rustc_middle[9d9ea3708d6e93f5]::query::erase::ErasedData<[u8; 8usize]>>, false>
  26:     0x7f38f18662e3 - rustc_query_impl[a298bd9aef25de82]::query_vtables::param_env::execute_query_non_incr::__rust_end_short_backtrace
  27:     0x7f38f2097a03 - rustc_hir_analysis[30f31704cfa60f6c]::check::wfcheck::check_type_defn
  28:     0x7f38f23ff1f2 - rustc_hir_analysis[30f31704cfa60f6c]::check::check::check_item_type
  29:     0x7f38f23f81a6 - rustc_hir_analysis[30f31704cfa60f6c]::check::wfcheck::check_well_formed
  30:     0x7f38f23f8187 - rustc_query_impl[a298bd9aef25de82]::query_vtables::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
  31:     0x7f38f23f77df - rustc_query_impl[a298bd9aef25de82]::execution::try_execute_query::<rustc_data_structures[ce2d1b2e5f4b9540]::vec_cache::VecCache<rustc_span[7b0e571682104a6f]::def_id::LocalDefId, rustc_middle[9d9ea3708d6e93f5]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[9d9ea3708d6e93f5]::dep_graph::graph::DepNodeIndex>, false>
  32:     0x7f38f23f7571 - rustc_query_impl[a298bd9aef25de82]::query_vtables::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
  33:     0x7f38f23f3420 - rustc_hir_analysis[30f31704cfa60f6c]::check::wfcheck::check_type_wf
  34:     0x7f38f23f331b - rustc_query_impl[a298bd9aef25de82]::query_vtables::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
  35:     0x7f38f2a11c49 - rustc_query_impl[a298bd9aef25de82]::execution::try_execute_query::<rustc_middle[9d9ea3708d6e93f5]::query::caches::SingleCache<rustc_middle[9d9ea3708d6e93f5]::query::erase::ErasedData<[u8; 1usize]>>, false>
  36:     0x7f38f2a11a2d - rustc_query_impl[a298bd9aef25de82]::query_vtables::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
  37:     0x7f38f2078c64 - rustc_hir_analysis[30f31704cfa60f6c]::check_crate
  38:     0x7f38f232c0ba - rustc_interface[473d810ada35544b]::passes::analysis
  39:     0x7f38f2a1354a - rustc_query_impl[a298bd9aef25de82]::execution::try_execute_query::<rustc_middle[9d9ea3708d6e93f5]::query::caches::SingleCache<rustc_middle[9d9ea3708d6e93f5]::query::erase::ErasedData<[u8; 0usize]>>, false>
  40:     0x7f38f2a132eb - rustc_query_impl[a298bd9aef25de82]::query_vtables::analysis::execute_query_non_incr::__rust_end_short_backtrace
  41:     0x7f38f2b85c6b - rustc_interface[473d810ada35544b]::interface::run_compiler::<(), rustc_driver_impl[56abbf040ce8585c]::run_compiler::{closure#0}>::{closure#2}
  42:     0x7f38f2bd7582 - std[29541300fb290a5d]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[473d810ada35544b]::util::run_in_thread_with_globals<rustc_interface[473d810ada35544b]::util::run_in_thread_pool_with_globals<rustc_interface[473d810ada35544b]::interface::run_compiler<(), rustc_driver_impl[56abbf040ce8585c]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  43:     0x7f38f2bd732d - <std[29541300fb290a5d]::thread::lifecycle::spawn_unchecked<rustc_interface[473d810ada35544b]::util::run_in_thread_with_globals<rustc_interface[473d810ada35544b]::util::run_in_thread_pool_with_globals<rustc_interface[473d810ada35544b]::interface::run_compiler<(), rustc_driver_impl[56abbf040ce8585c]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[460910d47b72e8ee]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  44:     0x7f38f2bd4d87 - <std[29541300fb290a5d]::sys::thread::unix::Thread>::new::thread_start
  45:     0x7f38ebe97739 - <unknown>
  46:     0x7f38ebf1bedc - <unknown>
  47:                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 1.100.0-nightly (b0ca9c712 2026-08-22) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [param_env] computing normalized predicates of `G`
#1 [check_well_formed] checking that `G` 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 4 previous errors; 2 warnings emitted

Some errors have detailed explanations: E0106, E0261, E0283, E0601.
For more information about an error, try `rustc --explain E0106`.

@rustbot label +F-supertrait_item_shadowing +F-generic_const_exprs

[malezjaa]

searched nightlies: from nightly-2026-06-26 to nightly-2026-09-12
regressed nightly: nightly-2026-06-29
searched commit range: 13f1859...df6ee90
regressed commit: fd07dbf

bisected with cargo-bisect-rustc v0.6.11

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --regress=ice --without-cargo

Exact pr: #152225

@rustbot label -needs-triage