ICE: delegation: index out of bounds #150673
Description
Code
#![feature(fn_delegation)]
mod first_example {
struct S<S>;
trait Trait {
reuse to_reuse::foo;
}
mod to_reuse {
fn foo<T>() -> T {}
}
impl Trait for S {
reuse foo;
}
}Meta
rustc --version --verbose:
rustc 1.94.0-nightly (7ecabfaaf 2026-01-03)
binary: rustc
commit-hash: 7ecabfaaf1a58172cdd71f7661cf6589ddf7928f
commit-date: 2026-01-03
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8
Error output
error[E0425]: cannot find function `foo` in this scope
--> code.rs:11:15
|
11 | reuse foo;
| ^^^ not found in this scope
|
note: function `first_example::to_reuse::foo` exists but is inaccessible
--> code.rs:8:9
|
8 | fn foo<T>() -> T {}
| ^^^^^^^^^^^^^^^^ not accessible
error[E0603]: function `foo` is private
--> code.rs:5:25
|
5 | reuse to_reuse::foo;
| ^^^ private function
|
note: the function `foo` is defined here
--> code.rs:8:9
|
8 | fn foo<T>() -> T {}
| ^^^^^^^^^^^^^^^^
warning: the feature `fn_delegation` is incomplete and may not be safe to use and/or cause compiler crashes
--> code.rs:1:12
|
1 | #![feature(fn_delegation)]
| ^^^^^^^^^^^^^
|
= note: see issue #118212 <https://github.com/rust-lang/rust/issues/118212> for more information
= note: `#[warn(incomplete_features)]` on by default
error[E0601]: `main` function not found in crate `code`
--> code.rs:13:2
|
13 | }
| ^ consider adding a `main` function to `code.rs`
error[E0107]: missing generics for struct `S`
--> code.rs:10:20
|
10 | impl Trait for S {
| ^ expected 1 generic argument
|
note: struct defined here, with 1 generic parameter: `S`
--> code.rs:3:12
|
3 | struct S<S>;
| ^ -
help: add missing generic argument
|
10 | impl Trait for S<S> {
| +++
Backtrace
thread 'rustc' (1254997) panicked at /rustc-dev/7ecabfaaf1a58172cdd71f7661cf6589ddf7928f/compiler/rustc_hir_analysis/src/variance/solve.rs:78:47:
index out of bounds: the len is 6 but the index is 6
stack backtrace:
0: 0x7fb776a313f3 - <<std[dfad6fe52c7ffb96]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[155fa69bcf1a74aa]::fmt::Display>::fmt
1: 0x7fb77700e2c8 - core[155fa69bcf1a74aa]::fmt::write
2: 0x7fb776a47b16 - <std[dfad6fe52c7ffb96]::sys::stdio::unix::Stderr as std[dfad6fe52c7ffb96]::io::Write>::write_fmt
3: 0x7fb776a07be8 - std[dfad6fe52c7ffb96]::panicking::default_hook::{closure#0}
4: 0x7fb776a25333 - std[dfad6fe52c7ffb96]::panicking::default_hook
5: 0x7fb775a0d37a - std[dfad6fe52c7ffb96]::panicking::update_hook::<alloc[52b53f39752dbf3]::boxed::Box<rustc_driver_impl[27820d298b08c973]::install_ice_hook::{closure#1}>>::{closure#0}
6: 0x7fb776a25612 - std[dfad6fe52c7ffb96]::panicking::panic_with_hook
7: 0x7fb776a07ca8 - std[dfad6fe52c7ffb96]::panicking::panic_handler::{closure#0}
8: 0x7fb7769fee19 - std[dfad6fe52c7ffb96]::sys::backtrace::__rust_end_short_backtrace::<std[dfad6fe52c7ffb96]::panicking::panic_handler::{closure#0}, !>
9: 0x7fb776a0975d - __rustc[4205645c07b58ae0]::rust_begin_unwind
10: 0x7fb7737427cc - core[155fa69bcf1a74aa]::panicking::panic_fmt
11: 0x7fb773ad7943 - core[155fa69bcf1a74aa]::panicking::panic_bounds_check
12: 0x7fb773a6b9d6 - rustc_hir_analysis[87ca905f401f0fa5]::variance::crate_variances
13: 0x7fb77819c670 - rustc_query_impl[6ad7e1bd79b807cf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6ad7e1bd79b807cf]::query_impl::crate_variances::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 8usize]>>
14: 0x7fb77819bbd9 - rustc_query_system[27e38e26a46ba8cb]::query::plumbing::try_execute_query::<rustc_query_impl[6ad7e1bd79b807cf]::DynamicConfig<rustc_query_system[27e38e26a46ba8cb]::query::caches::SingleCache<rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[6ad7e1bd79b807cf]::plumbing::QueryCtxt, false>
15: 0x7fb77819b200 - rustc_query_impl[6ad7e1bd79b807cf]::query_impl::crate_variances::get_query_non_incr::__rust_end_short_backtrace
16: 0x7fb777169297 - rustc_query_impl[6ad7e1bd79b807cf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6ad7e1bd79b807cf]::query_impl::variances_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 16usize]>>
17: 0x7fb777168e11 - <rustc_query_impl[6ad7e1bd79b807cf]::query_impl::variances_of::dynamic_query::{closure#2} as core[155fa69bcf1a74aa]::ops::function::FnOnce<(rustc_middle[4a73b4962f75d7b5]::ty::context::TyCtxt, rustc_span[3c3ff8aa0c1565a]::def_id::DefId)>>::call_once
18: 0x7fb7771673e1 - rustc_query_system[27e38e26a46ba8cb]::query::plumbing::try_execute_query::<rustc_query_impl[6ad7e1bd79b807cf]::DynamicConfig<rustc_query_system[27e38e26a46ba8cb]::query::caches::DefIdCache<rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[6ad7e1bd79b807cf]::plumbing::QueryCtxt, false>
19: 0x7fb777166f32 - rustc_query_impl[6ad7e1bd79b807cf]::query_impl::variances_of::get_query_non_incr::__rust_end_short_backtrace
20: 0x7fb7777c8435 - rustc_hir_analysis[87ca905f401f0fa5]::check::wfcheck::check_variances_for_type_defn
21: 0x7fb777667519 - rustc_hir_analysis[87ca905f401f0fa5]::check::check::check_item_type
22: 0x7fb777661e36 - rustc_hir_analysis[87ca905f401f0fa5]::check::wfcheck::check_well_formed
23: 0x7fb777661e17 - rustc_query_impl[6ad7e1bd79b807cf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6ad7e1bd79b807cf]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 1usize]>>
24: 0x7fb77766168d - rustc_query_system[27e38e26a46ba8cb]::query::plumbing::try_execute_query::<rustc_query_impl[6ad7e1bd79b807cf]::DynamicConfig<rustc_data_structures[d5655ec51fef7d7c]::vec_cache::VecCache<rustc_span[3c3ff8aa0c1565a]::def_id::LocalDefId, rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[27e38e26a46ba8cb]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[6ad7e1bd79b807cf]::plumbing::QueryCtxt, false>
25: 0x7fb777661196 - rustc_query_impl[6ad7e1bd79b807cf]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
26: 0x7fb77765e930 - rustc_hir_analysis[87ca905f401f0fa5]::check::wfcheck::check_type_wf
27: 0x7fb77765e81d - rustc_query_impl[6ad7e1bd79b807cf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6ad7e1bd79b807cf]::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 1usize]>>
28: 0x7fb778199388 - rustc_query_system[27e38e26a46ba8cb]::query::plumbing::try_execute_query::<rustc_query_impl[6ad7e1bd79b807cf]::DynamicConfig<rustc_query_system[27e38e26a46ba8cb]::query::caches::SingleCache<rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[6ad7e1bd79b807cf]::plumbing::QueryCtxt, false>
29: 0x7fb77819914e - rustc_query_impl[6ad7e1bd79b807cf]::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
30: 0x7fb777a52634 - rustc_hir_analysis[87ca905f401f0fa5]::check_crate
31: 0x7fb777ea489b - rustc_interface[efcfa671571f034]::passes::analysis
32: 0x7fb777ea44f5 - rustc_query_impl[6ad7e1bd79b807cf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6ad7e1bd79b807cf]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 0usize]>>
33: 0x7fb77819ab66 - rustc_query_system[27e38e26a46ba8cb]::query::plumbing::try_execute_query::<rustc_query_impl[6ad7e1bd79b807cf]::DynamicConfig<rustc_query_system[27e38e26a46ba8cb]::query::caches::SingleCache<rustc_middle[4a73b4962f75d7b5]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[6ad7e1bd79b807cf]::plumbing::QueryCtxt, false>
34: 0x7fb77819a736 - rustc_query_impl[6ad7e1bd79b807cf]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
35: 0x7fb778364711 - <rustc_interface[efcfa671571f034]::passes::create_and_enter_global_ctxt<core[155fa69bcf1a74aa]::option::Option<rustc_interface[efcfa671571f034]::queries::Linker>, rustc_driver_impl[27820d298b08c973]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[155fa69bcf1a74aa]::ops::function::FnOnce<(&rustc_session[7cf5aa466d461367]::session::Session, rustc_middle[4a73b4962f75d7b5]::ty::context::CurrentGcx, alloc[52b53f39752dbf3]::sync::Arc<rustc_data_structures[d5655ec51fef7d7c]::jobserver::Proxy>, &std[dfad6fe52c7ffb96]::sync::once_lock::OnceLock<rustc_middle[4a73b4962f75d7b5]::ty::context::GlobalCtxt>, &rustc_data_structures[d5655ec51fef7d7c]::sync::worker_local::WorkerLocal<rustc_middle[4a73b4962f75d7b5]::arena::Arena>, &rustc_data_structures[d5655ec51fef7d7c]::sync::worker_local::WorkerLocal<rustc_hir[a4563a91cd9984ff]::Arena>, rustc_driver_impl[27820d298b08c973]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
36: 0x7fb7781f36d8 - rustc_interface[efcfa671571f034]::interface::run_compiler::<(), rustc_driver_impl[27820d298b08c973]::run_compiler::{closure#0}>::{closure#1}
37: 0x7fb77816368e - std[dfad6fe52c7ffb96]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[efcfa671571f034]::util::run_in_thread_with_globals<rustc_interface[efcfa671571f034]::util::run_in_thread_pool_with_globals<rustc_interface[efcfa671571f034]::interface::run_compiler<(), rustc_driver_impl[27820d298b08c973]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
38: 0x7fb778163460 - <std[dfad6fe52c7ffb96]::thread::lifecycle::spawn_unchecked<rustc_interface[efcfa671571f034]::util::run_in_thread_with_globals<rustc_interface[efcfa671571f034]::util::run_in_thread_pool_with_globals<rustc_interface[efcfa671571f034]::interface::run_compiler<(), rustc_driver_impl[27820d298b08c973]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[155fa69bcf1a74aa]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
39: 0x7fb778168db8 - <std[dfad6fe52c7ffb96]::sys::thread::unix::Thread>::new::thread_start
40: 0x7fb771a9698b - <unknown>
41: 0x7fb771b1a9cc - <unknown>
42: 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: please attach the file at `/home/matthias/vcs/github/CRED/rustc-ice-2026-01-04T14_10_17-1254883.txt` to your bug report
note: rustc 1.94.0-nightly (7ecabfaaf 2026-01-03) running on x86_64-unknown-linux-gnu
query stack during panic:
#0 [crate_variances] computing the variances for items in this crate
#1 [variances_of] computing the variances of `first_example::S`
#2 [check_well_formed] checking that `first_example::S` is well-formed
#3 [check_type_wf] checking that types are well-formed
#4 [analysis] running analysis passes on crate `code`
end of query stack
error: aborting due to 4 previous errors; 1 warning emitted
Some errors have detailed explanations: E0107, E0425, E0601, E0603.
For more information about an error, try `rustc --explain E0107`.