ICE: const generic with default const expr specified before type generic causes compiler to crash

[w-utter]

The order of terms does not seem to be checked before trying to make a well-formedness check on a struct if a const expr is present in the constants default value.

I tried this code:

#![feature(generic_const_exprs)]

struct A<const N: usize = {2 + 1}, B = u8> {
    _i: [B; N]
}

And this code (which gave the right error message in rust-analyzer):

#![feature(generic_const_exprs)]

struct A<const N: usize = {2 + 1}, B> {
    _i: [B; N]
}

and both cause ICE's during compilation.

If the order of the parameters are switched, or the const expr for N is removed, then the compiler does not crash and either the expected error is reported, or successfully compiles.

Meta

rustc --version --verbose:

rustc 1.79.0-nightly (0d8b3346a 2024-04-14)
binary: rustc
commit-hash: 0d8b3346a3992ab11ea35ff0fb95a6864b91f797
commit-date: 2024-04-14
host: aarch64-apple-darwin
release: 1.79.0-nightly
LLVM version: 18.1.3

Backtrace

thread 'rustc' panicked at compiler/rustc_middle/src/ty/generic_args.rs:917:9:
Box<dyn Any>
stack backtrace:
   0:        0x103152cc0 - std::backtrace::Backtrace::create::hdc1994fcb4e8c481
   1:        0x10c850c08 - <alloc[b0dc11c95d7216a5]::boxed::Box<rustc_driver_impl[3cc9bf65ca00f6ee]::install_ice_hook::{closure#0}> as core[153a4a09f3d31382]::ops::function::Fn<(&dyn for<'a, 'b> core[153a4a09f3d31382]::ops::function::Fn<(&'a core[153a4a09f3d31382]::panic::panic_info::PanicInfo<'b>,), Output = ()> + core[153a4a09f3d31382]::marker::Sync + core[153a4a09f3d31382]::marker::Send, &core[153a4a09f3d31382]::panic::panic_info::PanicInfo)>>::call
   2:        0x10316bc74 - std::panicking::rust_panic_with_hook::h83d90448f6646b96
   3:        0x10c91590c - std[b70c874603df6a6]::panicking::begin_panic::<rustc_errors[8afa06678af9db0e]::ExplicitBug>::{closure#0}
   4:        0x10c915608 - std[b70c874603df6a6]::sys_common::backtrace::__rust_end_short_backtrace::<std[b70c874603df6a6]::panicking::begin_panic<rustc_errors[8afa06678af9db0e]::ExplicitBug>::{closure#0}, !>
   5:        0x1109db768 - std[b70c874603df6a6]::panicking::begin_panic::<rustc_errors[8afa06678af9db0e]::ExplicitBug>
   6:        0x10c8fb68c - <rustc_errors[8afa06678af9db0e]::diagnostic::BugAbort as rustc_errors[8afa06678af9db0e]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   7:        0x10d2e78c8 - rustc_middle[41002bb16f18dd76]::util::bug::opt_span_bug_fmt::<rustc_span[5f336a5c6a7d3b2b]::span_encoding::Span>::{closure#0}
   8:        0x10d2e6f38 - rustc_middle[41002bb16f18dd76]::ty::context::tls::with_opt::<rustc_middle[41002bb16f18dd76]::util::bug::opt_span_bug_fmt<rustc_span[5f336a5c6a7d3b2b]::span_encoding::Span>::{closure#0}, !>::{closure#0}
   9:        0x10d2e6f04 - rustc_middle[41002bb16f18dd76]::ty::context::tls::with_context_opt::<rustc_middle[41002bb16f18dd76]::ty::context::tls::with_opt<rustc_middle[41002bb16f18dd76]::util::bug::opt_span_bug_fmt<rustc_span[5f336a5c6a7d3b2b]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  10:        0x110a5ac9c - rustc_middle[41002bb16f18dd76]::util::bug::bug_fmt
  11:        0x110a5bbe8 - <rustc_middle[41002bb16f18dd76]::ty::generic_args::ArgFolder>::type_param_out_of_range
  12:        0x10d3237b4 - <rustc_middle[41002bb16f18dd76]::ty::generic_args::ArgFolder as rustc_type_ir[38402fc3e0792e7a]::fold::TypeFolder<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>::fold_ty
  13:        0x10d2f5dcc - <&rustc_middle[41002bb16f18dd76]::ty::list::RawList<(), rustc_middle[41002bb16f18dd76]::ty::generic_args::GenericArg> as rustc_type_ir[38402fc3e0792e7a]::fold::TypeFoldable<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>::try_fold_with::<rustc_middle[41002bb16f18dd76]::ty::generic_args::ArgFolder>
  14:        0x10d2eb6f4 - <rustc_type_ir[38402fc3e0792e7a]::predicate_kind::ClauseKind<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt> as rustc_type_ir[38402fc3e0792e7a]::fold::TypeFoldable<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>::try_fold_with::<rustc_middle[41002bb16f18dd76]::ty::generic_args::ArgFolder>
  15:        0x10d2fc044 - <rustc_middle[41002bb16f18dd76]::ty::sty::Binder<rustc_type_ir[38402fc3e0792e7a]::predicate_kind::PredicateKind<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>>::try_map_bound::<<rustc_middle[41002bb16f18dd76]::ty::sty::Binder<rustc_type_ir[38402fc3e0792e7a]::predicate_kind::PredicateKind<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>> as rustc_type_ir[38402fc3e0792e7a]::fold::TypeSuperFoldable<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>::try_super_fold_with<rustc_middle[41002bb16f18dd76]::ty::generic_args::ArgFolder>::{closure#0}, rustc_type_ir[38402fc3e0792e7a]::predicate_kind::PredicateKind<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>, !>
  16:        0x10d327eac - <rustc_middle[41002bb16f18dd76]::ty::predicate::Clause as rustc_type_ir[38402fc3e0792e7a]::fold::TypeFoldable<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>::try_fold_with::<rustc_middle[41002bb16f18dd76]::ty::generic_args::ArgFolder>
  17:        0x10d3c0224 - <rustc_middle[41002bb16f18dd76]::ty::generics::GenericPredicates>::instantiate_into
  18:        0x10e0ff520 - <rustc_trait_selection[903f6ad29f897722]::traits::wf::WfPredicates>::nominal_obligations
  19:        0x10e0fc594 - <rustc_trait_selection[903f6ad29f897722]::traits::wf::WfPredicates as rustc_type_ir[38402fc3e0792e7a]::visit::TypeVisitor<rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt>>::visit_const
  20:        0x10e0fa2b4 - rustc_trait_selection[903f6ad29f897722]::traits::wf::obligations
  21:        0x10e0d6c10 - <rustc_trait_selection[903f6ad29f897722]::traits::fulfill::FulfillProcessor as rustc_data_structures[b85285f53c509edc]::obligation_forest::ObligationProcessor>::process_obligation
  22:        0x10e0bfd08 - <rustc_data_structures[b85285f53c509edc]::obligation_forest::ObligationForest<rustc_trait_selection[903f6ad29f897722]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[903f6ad29f897722]::traits::fulfill::FulfillProcessor>
  23:        0x10e0d1c7c - <rustc_trait_selection[903f6ad29f897722]::traits::fulfill::FulfillmentContext as rustc_infer[7476a3dc73ea6c0d]::traits::engine::TraitEngine>::select_where_possible
  24:        0x10cbbcc14 - rustc_hir_analysis[2c387bcc114465b6]::check::wfcheck::check_type_defn
  25:        0x10cbb9c4c - rustc_hir_analysis[2c387bcc114465b6]::check::wfcheck::check_well_formed
  26:        0x10db6f0d4 - rustc_query_impl[816618de84ba844]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[816618de84ba844]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>
  27:        0x10dbff0b8 - <rustc_query_impl[816618de84ba844]::query_impl::check_well_formed::dynamic_query::{closure#2} as core[153a4a09f3d31382]::ops::function::FnOnce<(rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt, rustc_hir[895c406cf2976696]::hir_id::OwnerId)>>::call_once
  28:        0x10db22064 - rustc_query_system[4617ca2eed8c4435]::query::plumbing::try_execute_query::<rustc_query_impl[816618de84ba844]::DynamicConfig<rustc_query_system[4617ca2eed8c4435]::query::caches::VecCache<rustc_hir[895c406cf2976696]::hir_id::OwnerId, rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[816618de84ba844]::plumbing::QueryCtxt, true>
  29:        0x10dc02c9c - rustc_query_impl[816618de84ba844]::query_impl::check_well_formed::get_query_incr::__rust_end_short_backtrace
  30:        0x10cbe0068 - rustc_middle[41002bb16f18dd76]::query::plumbing::query_ensure_error_guaranteed::<rustc_query_system[4617ca2eed8c4435]::query::caches::VecCache<rustc_hir[895c406cf2976696]::hir_id::OwnerId, rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>, ()>
  31:        0x10cbdce94 - <rustc_data_structures[b85285f53c509edc]::sync::parallel::ParallelGuard>::run::<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_data_structures[b85285f53c509edc]::sync::parallel::enabled::try_par_for_each_in<&[rustc_hir[895c406cf2976696]::hir::ImplItemId], rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed, <rustc_middle[41002bb16f18dd76]::hir::ModuleItems>::par_impl_items<rustc_hir_analysis[2c387bcc114465b6]::check::wfcheck::check_mod_type_wf::{closure#1}>::{closure#0}>::{closure#0}::{closure#2}::{closure#0}>
  32:        0x10cb96440 - <rustc_middle[41002bb16f18dd76]::hir::ModuleItems>::par_items::<rustc_hir_analysis[2c387bcc114465b6]::check::wfcheck::check_mod_type_wf::{closure#0}>
  33:        0x10cbc0458 - rustc_hir_analysis[2c387bcc114465b6]::check::wfcheck::check_mod_type_wf
  34:        0x10db6f0b0 - rustc_query_impl[816618de84ba844]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[816618de84ba844]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>
  35:        0x10dc693c0 - <rustc_query_impl[816618de84ba844]::query_impl::check_mod_type_wf::dynamic_query::{closure#2} as core[153a4a09f3d31382]::ops::function::FnOnce<(rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt, rustc_span[5f336a5c6a7d3b2b]::def_id::LocalModDefId)>>::call_once
  36:        0x10dacaf80 - rustc_query_system[4617ca2eed8c4435]::query::plumbing::try_execute_query::<rustc_query_impl[816618de84ba844]::DynamicConfig<rustc_query_system[4617ca2eed8c4435]::query::caches::DefaultCache<rustc_span[5f336a5c6a7d3b2b]::def_id::LocalModDefId, rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[816618de84ba844]::plumbing::QueryCtxt, true>
  37:        0x10dd4ced4 - rustc_query_impl[816618de84ba844]::query_impl::check_mod_type_wf::get_query_incr::__rust_end_short_backtrace
  38:        0x10cbdd420 - <rustc_data_structures[b85285f53c509edc]::sync::parallel::ParallelGuard>::run::<(), rustc_data_structures[b85285f53c509edc]::sync::parallel::enabled::par_for_each_in<&rustc_hir[895c406cf2976696]::hir_id::OwnerId, &[rustc_hir[895c406cf2976696]::hir_id::OwnerId], <rustc_middle[41002bb16f18dd76]::hir::map::Map>::par_for_each_module<rustc_hir_analysis[2c387bcc114465b6]::check_crate::{closure#1}::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}::{closure#0}>
  39:        0x10cba5a80 - rustc_hir_analysis[2c387bcc114465b6]::check_crate
  40:        0x10cfca310 - rustc_interface[7886f7beac8da793]::passes::analysis
  41:        0x10db72968 - rustc_query_impl[816618de84ba844]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[816618de84ba844]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>
  42:        0x10dd2c7f8 - <rustc_query_impl[816618de84ba844]::query_impl::analysis::dynamic_query::{closure#2} as core[153a4a09f3d31382]::ops::function::FnOnce<(rustc_middle[41002bb16f18dd76]::ty::context::TyCtxt, ())>>::call_once
  43:        0x10da89c10 - rustc_query_system[4617ca2eed8c4435]::query::plumbing::try_execute_query::<rustc_query_impl[816618de84ba844]::DynamicConfig<rustc_query_system[4617ca2eed8c4435]::query::caches::SingleCache<rustc_middle[41002bb16f18dd76]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[816618de84ba844]::plumbing::QueryCtxt, true>
  44:        0x10dc6c644 - rustc_query_impl[816618de84ba844]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  45:        0x10c88c194 - <rustc_interface[7886f7beac8da793]::queries::QueryResult<&rustc_middle[41002bb16f18dd76]::ty::context::GlobalCtxt>>::enter::<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_driver_impl[3cc9bf65ca00f6ee]::run_compiler::{closure#0}::{closure#1}::{closure#3}>
  46:        0x10c874c50 - <rustc_interface[7886f7beac8da793]::interface::Compiler>::enter::<rustc_driver_impl[3cc9bf65ca00f6ee]::run_compiler::{closure#0}::{closure#1}, core[153a4a09f3d31382]::result::Result<core[153a4a09f3d31382]::option::Option<rustc_interface[7886f7beac8da793]::queries::Linker>, rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>
  47:        0x10c853628 - rustc_span[5f336a5c6a7d3b2b]::set_source_map::<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_interface[7886f7beac8da793]::interface::run_compiler<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_driver_impl[3cc9bf65ca00f6ee]::run_compiler::{closure#0}>::{closure#0}::{closure#0}>
  48:        0x10c88fbac - <scoped_tls[e07671f0187c90a4]::ScopedKey<rustc_span[5f336a5c6a7d3b2b]::SessionGlobals>>::set::<rustc_interface[7886f7beac8da793]::util::run_in_thread_with_globals<rustc_interface[7886f7beac8da793]::util::run_in_thread_pool_with_globals<rustc_interface[7886f7beac8da793]::interface::run_compiler<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_driver_impl[3cc9bf65ca00f6ee]::run_compiler::{closure#0}>::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#0}::{closure#0}::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>
  49:        0x10c85bf14 - std[b70c874603df6a6]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[7886f7beac8da793]::util::run_in_thread_with_globals<rustc_interface[7886f7beac8da793]::util::run_in_thread_pool_with_globals<rustc_interface[7886f7beac8da793]::interface::run_compiler<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_driver_impl[3cc9bf65ca00f6ee]::run_compiler::{closure#0}>::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>
  50:        0x10c8977b8 - <<std[b70c874603df6a6]::thread::Builder>::spawn_unchecked_<rustc_interface[7886f7beac8da793]::util::run_in_thread_with_globals<rustc_interface[7886f7beac8da793]::util::run_in_thread_pool_with_globals<rustc_interface[7886f7beac8da793]::interface::run_compiler<core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>, rustc_driver_impl[3cc9bf65ca00f6ee]::run_compiler::{closure#0}>::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[153a4a09f3d31382]::result::Result<(), rustc_span[5f336a5c6a7d3b2b]::ErrorGuaranteed>>::{closure#2} as core[153a4a09f3d31382]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  51:        0x1031746fc - std::sys::pal::unix::thread::Thread::new::thread_start::h56bc2156fc274a0f
  52:        0x188e02034 - __pthread_joiner_wake


rustc version: 1.79.0-nightly (0d8b3346a 2024-04-14)
platform: aarch64-apple-darwin

query stack during panic:
#0 [check_well_formed] checking that `A` is well-formed
#1 [check_mod_type_wf] checking that types are well-formed in top-level module
#2 [analysis] running analysis passes on this crate
end of query stack

[compiler-errors]

I'm pretty sure this is a duplicate of #106994