Cycle error happens when using inherent_associated_types and generic_const_exprs features

[EvanLuo42]

Code

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

struct B<const A: usize>;

struct Test<const A: usize>;

impl<const A: usize> Test<A> {
    type B = B<{ A }>;
    
    fn test(a: Self::B) -> Self::B {
        a
    }
}

Meta

rustc --version --verbose:

rustc 1.86.0-nightly (942db6782 2025-02-06)
binary: rustc
commit-hash: 942db6782f4a28c55b0b75b38fd4394d0483390f
commit-date: 2025-02-06
host: aarch64-apple-darwin
release: 1.86.0-nightly
LLVM version: 19.1.7

Error output

error: internal compiler error[E0391]: cycle detected when computing function signature of `<impl at src/lib.rs:9:1: 9:29>::test`
  --> src/lib.rs:12:5
   |
12 |     fn test(a: Self::B) -> Self::B {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: ...which requires computing normalized predicates of `<impl at src/lib.rs:9:1: 9:29>::test`...
  --> src/lib.rs:12:5
   |
12 |     fn test(a: Self::B) -> Self::B {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires computing predicates of `<impl at src/lib.rs:9:1: 9:29>::test`...
  --> src/lib.rs:12:5
   |
12 |     fn test(a: Self::B) -> Self::B {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires computing explicit predicates of `<impl at src/lib.rs:9:1: 9:29>::test`...
  --> src/lib.rs:12:5
   |
12 |     fn test(a: Self::B) -> Self::B {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: ...which again requires computing function signature of `<impl at src/lib.rs:9:1: 9:29>::test`, completing the cycle
   = note: cycle used when computing the variances for items in this crate
   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
note: delayed at compiler/rustc_query_system/src/query/job.rs:563:16 - disabled backtrace
  --> src/lib.rs:12:5
   |
12 |     fn test(a: Self::B) -> Self::B {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Backtrace

note: delayed at compiler/rustc_query_system/src/query/job.rs:563:16
         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::diagnostic::Diag>::delay_as_bug
         4: rustc_query_system::query::plumbing::mk_cycle::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::consts::valtree::Value, rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt>
         5: rustc_query_system::query::plumbing::cycle_error::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::consts::valtree::Value, rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt>
         6: 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>
         7: rustc_query_impl::query_impl::fn_sig::get_query_non_incr::__rust_end_short_backtrace
         8: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>>
         9: rustc_hir_analysis::collect::predicates_of::gather_explicit_predicates_of
        10: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::explicit_predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
        11: 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>
        12: rustc_query_impl::query_impl::explicit_predicates_of::get_query_non_incr::__rust_end_short_backtrace
        13: rustc_hir_analysis::collect::predicates_of::predicates_of
        14: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
        15: 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>
        16: rustc_query_impl::query_impl::predicates_of::get_query_non_incr::__rust_end_short_backtrace
        17: rustc_ty_utils::ty::param_env
        18: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::param_env::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::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        20: rustc_query_impl::query_impl::param_env::get_query_non_incr::__rust_end_short_backtrace
        21: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>>
        22: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_assoc_path
        23: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty
        24: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_fn_ty
        25: rustc_hir_analysis::collect::lower_fn_sig_recovering_infer_ret_ty
        26: rustc_hir_analysis::collect::fn_sig
        27: 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]>>
        28: <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
        29: 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>
        30: rustc_query_impl::query_impl::fn_sig::get_query_non_incr::__rust_end_short_backtrace
        31: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>>
        32: <rustc_hir_analysis::variance::constraints::ConstraintContext>::build_constraints_for_item
        33: rustc_hir_analysis::variance::crate_variances
        34: 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]>>
        35: 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>
        36: rustc_query_impl::query_impl::crate_variances::get_query_non_incr::__rust_end_short_backtrace
        37: rustc_hir_analysis::variance::variances_of
        38: 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]>>
        39: <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
        40: 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>
        41: rustc_query_impl::query_impl::variances_of::get_query_non_incr::__rust_end_short_backtrace
        42: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 16]>>>
        43: rustc_hir_analysis::check::wfcheck::check_variances_for_type_defn
        44: rustc_hir_analysis::check::wfcheck::check_well_formed
        45: 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]>>
        46: 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>
        47: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
        48: rustc_hir_analysis::check::wfcheck::check_mod_type_wf
        49: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        50: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalModDefId, rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        51: rustc_query_impl::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
        52: rustc_hir_analysis::check_crate
        53: rustc_interface::passes::run_required_analyses
        54: rustc_interface::passes::analysis
        55: 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]>>
        56: 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>
        57: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        58: 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}::{closure#0}
        59: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        60: 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}, ()>
        61: <<std::thread::Builder>::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}
        62: std::sys::pal::unix::thread::Thread::new::thread_start
        63: <unknown>
        64: clone
  --> src/lib.rs:12:5
   |
12 |     fn test(a: Self::B) -> Self::B {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^