ICE `None` in compiler/rustc_middle/src/ty/sty.rs

[matthiaskrgr]

original:

#![feature(min_generic_const_args)]
#![feature(inherent_associated_types)]
struct Foo<'a> {
    x: &'a (),
}

impl<'a> Foo<'a> {
    fn foo(_: [u8; Foo::X]) { std::mem::transmute([4]) }
}

fn main() {}

Version information

rustc 1.94.0-nightly (cec70080f 2025-12-15)
binary: rustc
commit-hash: cec70080fd441d16e9fb08a0d1d1a04c72d1ed25
commit-date: 2025-12-15
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8

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

Program output

warning: the feature `min_generic_const_args` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/crash.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

warning: the feature `inherent_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/crash.rs:2:12
  |
2 | #![feature(inherent_associated_types)]
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #8995 <https://github.com/rust-lang/rust/issues/8995> for more information

warning: struct `Foo` is never constructed
 --> /tmp/crash.rs:3:8
  |
3 | struct Foo<'a> {
  |        ^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: associated function `foo` is never used
 --> /tmp/crash.rs:8:8
  |
7 | impl<'a> Foo<'a> {
  | ---------------- associated function in this implementation
8 |     fn foo(_: [u8; Foo::X]) { std::mem::transmute([4]) }
  |        ^^^


thread 'rustc' (2084098) panicked at compiler/rustc_middle/src/ty/sty.rs:2104:27:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0:     0x7f5d57d8a253 - <<std[5ec89fed4875b12f]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[26a7a51be8c9f870]::fmt::Display>::fmt
   1:     0x7f5d58410708 - core[26a7a51be8c9f870]::fmt::write
   2:     0x7f5d57da08a6 - <std[5ec89fed4875b12f]::sys::stdio::unix::Stderr as std[5ec89fed4875b12f]::io::Write>::write_fmt
   3:     0x7f5d57d60a18 - std[5ec89fed4875b12f]::panicking::default_hook::{closure#0}
   4:     0x7f5d57d7e123 - std[5ec89fed4875b12f]::panicking::default_hook
   5:     0x7f5d56d6ffb7 - std[5ec89fed4875b12f]::panicking::update_hook::<alloc[673ccbb8a4c5d329]::boxed::Box<rustc_driver_impl[50f6efb3f18c5e4b]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f5d57d7e402 - std[5ec89fed4875b12f]::panicking::panic_with_hook
   7:     0x7f5d57d60b0a - std[5ec89fed4875b12f]::panicking::panic_handler::{closure#0}
   8:     0x7f5d57d55389 - std[5ec89fed4875b12f]::sys::backtrace::__rust_end_short_backtrace::<std[5ec89fed4875b12f]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f5d57d6268d - __rustc[c625ac833ac53d73]::rust_begin_unwind
  10:     0x7f5d5523924c - core[26a7a51be8c9f870]::panicking::panic_fmt
  11:     0x7f5d54574782 - core[26a7a51be8c9f870]::panicking::panic
  12:     0x7f5d54e72f19 - core[26a7a51be8c9f870]::option::unwrap_failed
  13:     0x7f5d58db31d4 - <rustc_lint[87c3c4e0ddf52cb1]::BuiltinCombinedModuleLateLintPass as rustc_lint[87c3c4e0ddf52cb1]::passes::LateLintPass>::check_expr
  14:     0x7f5d58d826a6 - <rustc_lint[87c3c4e0ddf52cb1]::late::LateContextAndPass<rustc_lint[87c3c4e0ddf52cb1]::BuiltinCombinedModuleLateLintPass> as rustc_hir[6a9da475a5f9b785]::intravisit::Visitor>::visit_expr
  15:     0x7f5d58d82b1b - <rustc_lint[87c3c4e0ddf52cb1]::late::LateContextAndPass<rustc_lint[87c3c4e0ddf52cb1]::BuiltinCombinedModuleLateLintPass> as rustc_hir[6a9da475a5f9b785]::intravisit::Visitor>::visit_expr
  16:     0x7f5d58d817f2 - <rustc_lint[87c3c4e0ddf52cb1]::late::LateContextAndPass<rustc_lint[87c3c4e0ddf52cb1]::BuiltinCombinedModuleLateLintPass> as rustc_hir[6a9da475a5f9b785]::intravisit::Visitor>::visit_block
  17:     0x7f5d58d90a8d - <rustc_lint[87c3c4e0ddf52cb1]::late::LateContextAndPass<rustc_lint[87c3c4e0ddf52cb1]::BuiltinCombinedModuleLateLintPass> as rustc_hir[6a9da475a5f9b785]::intravisit::Visitor>::visit_nested_body
  18:     0x7f5d58d8aa15 - <rustc_lint[87c3c4e0ddf52cb1]::late::LateContextAndPass<rustc_lint[87c3c4e0ddf52cb1]::BuiltinCombinedModuleLateLintPass> as rustc_hir[6a9da475a5f9b785]::intravisit::Visitor>::visit_nested_item
  19:     0x7f5d58d88da2 - rustc_lint[87c3c4e0ddf52cb1]::lint_mod
  20:     0x7f5d58d88957 - rustc_query_impl[27139b72c8912d2b]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[27139b72c8912d2b]::query_impl::lint_mod::dynamic_query::{closure#2}::{closure#0}, rustc_middle[7d117b0519601dc6]::query::erase::Erased<[u8; 0usize]>>
  21:     0x7f5d591b8031 - rustc_query_system[5d3859f1d59bc7f3]::query::plumbing::try_execute_query::<rustc_query_impl[27139b72c8912d2b]::DynamicConfig<rustc_query_system[5d3859f1d59bc7f3]::query::caches::DefaultCache<rustc_span[ae684922c33956fd]::def_id::LocalModDefId, rustc_middle[7d117b0519601dc6]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[27139b72c8912d2b]::plumbing::QueryCtxt, false>
  22:     0x7f5d591b41fd - rustc_query_impl[27139b72c8912d2b]::query_impl::lint_mod::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7f5d591b3d90 - rustc_lint[87c3c4e0ddf52cb1]::late::check_crate::{closure#1}
  24:     0x7f5d591b397a - rustc_lint[87c3c4e0ddf52cb1]::late::check_crate
  25:     0x7f5d586aa10e - rustc_interface[b41716356610a9ea]::passes::analysis
  26:     0x7f5d586a9825 - rustc_query_impl[27139b72c8912d2b]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[27139b72c8912d2b]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[7d117b0519601dc6]::query::erase::Erased<[u8; 0usize]>>
  27:     0x7f5d595b1526 - rustc_query_system[5d3859f1d59bc7f3]::query::plumbing::try_execute_query::<rustc_query_impl[27139b72c8912d2b]::DynamicConfig<rustc_query_system[5d3859f1d59bc7f3]::query::caches::SingleCache<rustc_middle[7d117b0519601dc6]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[27139b72c8912d2b]::plumbing::QueryCtxt, false>
  28:     0x7f5d595b10f6 - rustc_query_impl[27139b72c8912d2b]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f5d5975fc51 - <rustc_interface[b41716356610a9ea]::passes::create_and_enter_global_ctxt<core[26a7a51be8c9f870]::option::Option<rustc_interface[b41716356610a9ea]::queries::Linker>, rustc_driver_impl[50f6efb3f18c5e4b]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[26a7a51be8c9f870]::ops::function::FnOnce<(&rustc_session[276d18328e744fa4]::session::Session, rustc_middle[7d117b0519601dc6]::ty::context::CurrentGcx, alloc[673ccbb8a4c5d329]::sync::Arc<rustc_data_structures[32d4a3d751e78af5]::jobserver::Proxy>, &std[5ec89fed4875b12f]::sync::once_lock::OnceLock<rustc_middle[7d117b0519601dc6]::ty::context::GlobalCtxt>, &rustc_data_structures[32d4a3d751e78af5]::sync::worker_local::WorkerLocal<rustc_middle[7d117b0519601dc6]::arena::Arena>, &rustc_data_structures[32d4a3d751e78af5]::sync::worker_local::WorkerLocal<rustc_hir[6a9da475a5f9b785]::Arena>, rustc_driver_impl[50f6efb3f18c5e4b]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  30:     0x7f5d595ed2da - rustc_interface[b41716356610a9ea]::interface::run_compiler::<(), rustc_driver_impl[50f6efb3f18c5e4b]::run_compiler::{closure#0}>::{closure#1}
  31:     0x7f5d5955f7ce - std[5ec89fed4875b12f]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[b41716356610a9ea]::util::run_in_thread_with_globals<rustc_interface[b41716356610a9ea]::util::run_in_thread_pool_with_globals<rustc_interface[b41716356610a9ea]::interface::run_compiler<(), rustc_driver_impl[50f6efb3f18c5e4b]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  32:     0x7f5d5955f5a0 - <std[5ec89fed4875b12f]::thread::lifecycle::spawn_unchecked<rustc_interface[b41716356610a9ea]::util::run_in_thread_with_globals<rustc_interface[b41716356610a9ea]::util::run_in_thread_pool_with_globals<rustc_interface[b41716356610a9ea]::interface::run_compiler<(), rustc_driver_impl[50f6efb3f18c5e4b]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[26a7a51be8c9f870]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7f5d5955d978 - <std[5ec89fed4875b12f]::sys::thread::unix::Thread>::new::thread_start
  34:     0x7f5d52e969cb - <unknown>
  35:     0x7f5d52f1aa0c - <unknown>
  36:                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 `/tmp/im/rustc-ice-2025-12-16T06_24_54-2084080.txt` to your bug report

query stack during panic:
#0 [lint_mod] linting top-level module
#1 [analysis] running analysis passes on crate `crash`
end of query stack
warning: 4 warnings emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: unelided lifetime in signature
 --> /tmp/crash.rs:8:20
  |
8 |     fn foo(_: [u8; Foo::X]) { std::mem::transmute([4]) }
  |                    ^^^
  |
note: delayed at compiler/rustc_hir_analysis/src/collect.rs:334:13
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
         2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
         3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, &str>
         4: <rustc_hir_analysis::collect::ItemCtxt as rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::re_infer
         5: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_resolved_ty_path
         6: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
         7: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_const_arg
         8: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
         9: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_fn_ty
        10: rustc_hir_analysis::collect::lower_fn_sig_recovering_infer_ret_ty
        11: rustc_hir_analysis::collect::fn_sig
        12: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::fn_sig::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
        13: <rustc_query_impl::query_impl::fn_sig::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::DefId)>>::call_once
        14: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        15: rustc_query_impl::query_impl::fn_sig::get_query_non_incr::__rust_end_short_backtrace
        16: <rustc_hir_analysis::variance::constraints::ConstraintContext>::build_constraints_for_item
        17: rustc_hir_analysis::variance::crate_variances
        18: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::crate_variances::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
        19: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        20: rustc_query_impl::query_impl::crate_variances::get_query_non_incr::__rust_end_short_backtrace
        21: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::variances_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 16]>>.warm
        22: <rustc_query_impl::query_impl::variances_of::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::DefId)>>::call_once
        23: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 16]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        24: rustc_query_impl::query_impl::variances_of::get_query_non_incr::__rust_end_short_backtrace
        25: rustc_hir_analysis::check::wfcheck::check_variances_for_type_defn
        26: rustc_hir_analysis::check::check::check_item_type
        27: rustc_hir_analysis::check::wfcheck::check_well_formed
        28: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        29: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        30: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
        31: rustc_hir_analysis::check::wfcheck::check_type_wf
        32: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        33: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        34: rustc_query_impl::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
        35: rustc_hir_analysis::check_crate
        36: rustc_interface::passes::analysis
        37: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
        38: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        39: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        40: <rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
        41: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        42: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
        43: <std::thread::lifecycle::spawn_unchecked<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
        44: <std::sys::thread::unix::Thread>::new::thread_start
        45: <unknown>
        46: <unknown>

 --> /tmp/crash.rs:8:20
  |
8 |     fn foo(_: [u8; Foo::X]) { std::mem::transmute([4]) }
  |                    ^^^

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 `/tmp/im/rustc-ice-2025-12-16T06_24_54-2084080.txt` to your bug report

query stack during panic:
end of query stack

@rustbot label +F-min_generic_const_args +F-inherent_associated_types

[matthiaskrgr]

since #148771

[reddevilmidzy]

Should we consider this as different from #148949?

[matthiaskrgr]

the code in #148949 is different and it does not reproduce the

thread 'rustc' (2613818) panicked at compiler/rustc_middle/src/ty/sty.rs:2104:27:
called `Option::unwrap()` on a `None` value