ICE on `typeof(CT_PARAM)` due to incorrect generic param substitution / instantiation somewhere

[brutalsavage]

Code

#![feature(generic_const_exprs)]

const fn make_tuple<const N: usize>() -> (u8::N) {
}
type TupleConst<const N: usize> = typeof(make_tuple::<N>());

Meta

rustc --version --verbose:

rustc 1.91.0-nightly (9c27f27ea 2025-09-08)
binary: rustc
commit-hash: 9c27f27ea3bab79a2fec827ef3ae0009959d60f4
commit-date: 2025-09-08
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.0

Error output

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> test.fuzz:1:12
  |
1 | #![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

warning: unnecessary parentheses around type
 --> test.fuzz:3:42
  |
3 | const fn make_tuple<const N: usize>() -> (u8::N) {
  |                                          ^     ^
  |
  = note: `#[warn(unused_parens)]` (part of `#[warn(unused)]`) on by default
help: remove these parentheses
  |
3 - const fn make_tuple<const N: usize>() -> (u8::N) {
3 + const fn make_tuple<const N: usize>() -> u8::N {
  |

error[E0601]: `main` function not found in crate `test`
 --> test.fuzz:5:61
  |
5 | type TupleConst<const N: usize> = typeof(make_tuple::<N>());
  |                                                             ^ consider adding a `main` function to `test.fuzz`

error[E0223]: ambiguous associated type
 --> test.fuzz:3:43
  |
3 | const fn make_tuple<const N: usize>() -> (u8::N) {
  |                                           ^^^^^
  |
help: if there were a trait named `Example` with associated type `N` implemented for `u8`, you could use the fully-qualified path
  |
3 - const fn make_tuple<const N: usize>() -> (u8::N) {
3 + const fn make_tuple<const N: usize>() -> (<u8 as Example>::N) {
  |

error: internal compiler error: compiler/rustc_middle/src/ty/sty.rs:372:13: cannot find `N/#0` in param-env: ParamEnv {
                                    caller_bounds: [],
                                }

thread 'rustc' (3869642) panicked at compiler/rustc_middle/src/ty/sty.rs:372:13:
Box<dyn Any>

Backtrace

stack backtrace:
   0:     0x7fca785afec3 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hf30880b118ce69a7
   1:     0x7fca78c01bd8 - core::fmt::write::h2adee94c9530c769
   2:     0x7fca78564cf1 - std::io::Write::write_fmt::hf9fd682cd305994d
   3:     0x7fca78575e12 - std::sys::backtrace::BacktraceLock::print::h2e8eaa47e6244167
   4:     0x7fca7857bd59 - std::panicking::default_hook::{{closure}}::hce66ca19674736b6
   5:     0x7fca7857b883 - std::panicking::default_hook::h378eb22e7f245ba6
   6:     0x7fca775c3707 - std[60f4c921464387a8]::panicking::update_hook::<alloc[af66c0f7f367d3a4]::boxed::Box<rustc_driver_impl[6e5208ea2b150886]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7fca7857c17f - std::panicking::panic_with_hook::h107561c887d41fb4
   8:     0x7fca775ffdc1 - std[60f4c921464387a8]::panicking::begin_panic::<rustc_errors[a4bc384b506279c9]::ExplicitBug>::{closure#0}
   9:     0x7fca775f37a6 - std[60f4c921464387a8]::sys::backtrace::__rust_end_short_backtrace::<std[60f4c921464387a8]::panicking::begin_panic<rustc_errors[a4bc384b506279c9]::ExplicitBug>::{closure#0}, !>
  10:     0x7fca775f3435 - std[60f4c921464387a8]::panicking::begin_panic::<rustc_errors[a4bc384b506279c9]::ExplicitBug>
  11:     0x7fca7760b551 - <rustc_errors[a4bc384b506279c9]::diagnostic::BugAbort as rustc_errors[a4bc384b506279c9]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x7fca77ba508a - rustc_middle[62f76fb1ad15f043]::util::bug::opt_span_bug_fmt::<rustc_span[84d5e499882068e4]::span_encoding::Span>::{closure#0}
  13:     0x7fca77ba524a - rustc_middle[62f76fb1ad15f043]::ty::context::tls::with_opt::<rustc_middle[62f76fb1ad15f043]::util::bug::opt_span_bug_fmt<rustc_span[84d5e499882068e4]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7fca77b93e1b - rustc_middle[62f76fb1ad15f043]::ty::context::tls::with_context_opt::<rustc_middle[62f76fb1ad15f043]::ty::context::tls::with_opt<rustc_middle[62f76fb1ad15f043]::util::bug::opt_span_bug_fmt<rustc_span[84d5e499882068e4]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7fca74cc2560 - rustc_middle[62f76fb1ad15f043]::util::bug::bug_fmt
  16:     0x7fca794dd78b - <rustc_trait_selection[15dd98a8352583f4]::traits::fulfill::FulfillProcessor as rustc_data_structures[d45417cb7c5e80c2]::obligation_forest::ObligationProcessor>::process_obligation
  17:     0x7fca78c04e49 - <rustc_data_structures[d45417cb7c5e80c2]::obligation_forest::ObligationForest<rustc_trait_selection[15dd98a8352583f4]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[15dd98a8352583f4]::traits::fulfill::FulfillProcessor>
  18:     0x7fca7925dd4b - <rustc_hir_typeck[4caaa11dff9d1644]::fn_ctxt::FnCtxt>::check_expr_call
  19:     0x7fca792873e7 - <rustc_hir_typeck[4caaa11dff9d1644]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  20:     0x7fca79117a91 - rustc_hir_typeck[4caaa11dff9d1644]::typeck_with_inspect::{closure#0}
  21:     0x7fca79112836 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>>
  22:     0x7fca78e2f345 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_data_structures[d45417cb7c5e80c2]::vec_cache::VecCache<rustc_span[84d5e499882068e4]::def_id::LocalDefId, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[36926af04fc30fbf]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  23:     0x7fca78e2ed89 - rustc_query_impl[d503ea7333d9f192]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  24:     0x7fca78e18582 - rustc_hir_analysis[84a042027edab4a]::collect::type_of::type_of
  25:     0x7fca78c1c7e6 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>>
  26:     0x7fca78c1b479 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_query_system[36926af04fc30fbf]::query::caches::DefIdCache<rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  27:     0x7fca78c1b01d - rustc_query_impl[d503ea7333d9f192]::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7fca7963bdcc - <dyn rustc_hir_analysis[84a042027edab4a]::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
  29:     0x7fca78e16a28 - rustc_hir_analysis[84a042027edab4a]::collect::type_of::type_of
  30:     0x7fca78c1c7e6 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>>
  31:     0x7fca78c1b479 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_query_system[36926af04fc30fbf]::query::caches::DefIdCache<rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  32:     0x7fca78c1b01d - rustc_query_impl[d503ea7333d9f192]::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
  33:     0x7fca79613973 - rustc_hir_analysis[84a042027edab4a]::check::check::check_item_type
  34:     0x7fca7960bc27 - rustc_hir_analysis[84a042027edab4a]::check::wfcheck::check_well_formed
  35:     0x7fca7960bc09 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 1usize]>>
  36:     0x7fca7960b449 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_data_structures[d45417cb7c5e80c2]::vec_cache::VecCache<rustc_span[84d5e499882068e4]::def_id::LocalDefId, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[36926af04fc30fbf]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  37:     0x7fca7960af56 - rustc_query_impl[d503ea7333d9f192]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  38:     0x7fca79607075 - rustc_hir_analysis[84a042027edab4a]::check::wfcheck::check_type_wf
  39:     0x7fca79606f65 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 1usize]>>
  40:     0x7fca79c09048 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_query_system[36926af04fc30fbf]::query::caches::SingleCache<rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  41:     0x7fca79c08e0e - rustc_query_impl[d503ea7333d9f192]::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
  42:     0x7fca78e3a539 - rustc_hir_analysis[84a042027edab4a]::check_crate
  43:     0x7fca78e272f0 - rustc_interface[f234d5aad18497a0]::passes::analysis
  44:     0x7fca78e26fa1 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 0usize]>>
  45:     0x7fca79c0f526 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_query_system[36926af04fc30fbf]::query::caches::SingleCache<rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  46:     0x7fca79c0f17c - rustc_query_impl[d503ea7333d9f192]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  47:     0x7fca79ed35a4 - rustc_interface[f234d5aad18497a0]::passes::create_and_enter_global_ctxt::<core[494a681d6e07a62e]::option::Option<rustc_interface[f234d5aad18497a0]::queries::Linker>, rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  48:     0x7fca79e734be - rustc_interface[f234d5aad18497a0]::interface::run_compiler::<(), rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}>::{closure#1}
  49:     0x7fca79db3c78 - std[60f4c921464387a8]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[f234d5aad18497a0]::util::run_in_thread_with_globals<rustc_interface[f234d5aad18497a0]::util::run_in_thread_pool_with_globals<rustc_interface[f234d5aad18497a0]::interface::run_compiler<(), rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  50:     0x7fca79db395c - <<std[60f4c921464387a8]::thread::Builder>::spawn_unchecked_<rustc_interface[f234d5aad18497a0]::util::run_in_thread_with_globals<rustc_interface[f234d5aad18497a0]::util::run_in_thread_pool_with_globals<rustc_interface[f234d5aad18497a0]::interface::run_compiler<(), rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[494a681d6e07a62e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  51:     0x7fca79db9e8d - std::sys::pal::unix::thread::Thread::new::thread_start::h0ed16f40fa4b751a
  52:     0x7fca7386bac3 - start_thread
                               at ./nptl/pthread_create.c:442:8
  53:     0x7fca738fd850 - __GI___clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81:0
  54:                0x0 - <unknown>

[cyrgani]

another variant:

type TupleConst<const N: usize> = typeof(N);

thread 'rustc' (38) panicked at compiler/rustc_middle/src/ty/generics.rs:221:29:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0:     0x7d3a5c1afec3 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hf30880b118ce69a7
   1:     0x7d3a5c801bd8 - core::fmt::write::h2adee94c9530c769
   2:     0x7d3a5c164cf1 - std::io::Write::write_fmt::hf9fd682cd305994d
   3:     0x7d3a5c175e12 - std::sys::backtrace::BacktraceLock::print::h2e8eaa47e6244167
   4:     0x7d3a5c17bd59 - std::panicking::default_hook::{{closure}}::hce66ca19674736b6
   5:     0x7d3a5c17b883 - std::panicking::default_hook::h378eb22e7f245ba6
   6:     0x7d3a5b1c3707 - std[60f4c921464387a8]::panicking::update_hook::<alloc[af66c0f7f367d3a4]::boxed::Box<rustc_driver_impl[6e5208ea2b150886]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7d3a5c17c17f - std::panicking::panic_with_hook::h107561c887d41fb4
   8:     0x7d3a5c17bf3a - std::panicking::panic_handler::{{closure}}::h22ca1e42f3e34cf3
   9:     0x7d3a5c175f49 - std::sys::backtrace::__rust_end_short_backtrace::h2a269d3827952e51
  10:     0x7d3a5c15672d - __rustc[46dfa2e28c3cccbc]::rust_begin_unwind
  11:     0x7d3a588bf8f0 - core::panicking::panic_fmt::hb26515e908d4a63d
  12:     0x7d3a5a8595f3 - core::panicking::panic_bounds_check::hc62e1336fc189dbe
  13:     0x7d3a5e0c91d0 - <rustc_middle[62f76fb1ad15f043]::ty::generics::Generics>::param_at.cold
  14:     0x7d3a5d17677e - <rustc_borrowck[88e9fac1b60137e7]::type_check::TypeChecker as rustc_middle[62f76fb1ad15f043]::mir::visit::Visitor>::visit_const_operand
  15:     0x7d3a5d86b957 - <rustc_borrowck[88e9fac1b60137e7]::type_check::TypeChecker as rustc_middle[62f76fb1ad15f043]::mir::visit::Visitor>::visit_body
  16:     0x7d3a5d837522 - rustc_borrowck[88e9fac1b60137e7]::type_check::type_check
  17:     0x7d3a5da432c9 - <rustc_borrowck[88e9fac1b60137e7]::root_cx::BorrowCheckRootCtxt>::do_mir_borrowck
  18:     0x7d3a5da3b6e4 - rustc_borrowck[88e9fac1b60137e7]::mir_borrowck
  19:     0x7d3a5da3b49d - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>>
  20:     0x7d3a5ca2f345 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_data_structures[d45417cb7c5e80c2]::vec_cache::VecCache<rustc_span[84d5e499882068e4]::def_id::LocalDefId, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[36926af04fc30fbf]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  21:     0x7d3a5ca2eb49 - rustc_query_impl[d503ea7333d9f192]::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
  22:     0x7d3a5ca2a289 - <rustc_middle[62f76fb1ad15f043]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[f234d5aad18497a0]::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
  23:     0x7d3a5ca27b0b - rustc_interface[f234d5aad18497a0]::passes::analysis
  24:     0x7d3a5ca26fa1 - rustc_query_impl[d503ea7333d9f192]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d503ea7333d9f192]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 0usize]>>
  25:     0x7d3a5d80f526 - rustc_query_system[36926af04fc30fbf]::query::plumbing::try_execute_query::<rustc_query_impl[d503ea7333d9f192]::DynamicConfig<rustc_query_system[36926af04fc30fbf]::query::caches::SingleCache<rustc_middle[62f76fb1ad15f043]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[d503ea7333d9f192]::plumbing::QueryCtxt, false>
  26:     0x7d3a5d80f17c - rustc_query_impl[d503ea7333d9f192]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  27:     0x7d3a5dad35a4 - rustc_interface[f234d5aad18497a0]::passes::create_and_enter_global_ctxt::<core[494a681d6e07a62e]::option::Option<rustc_interface[f234d5aad18497a0]::queries::Linker>, rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  28:     0x7d3a5da734be - rustc_interface[f234d5aad18497a0]::interface::run_compiler::<(), rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}>::{closure#1}
  29:     0x7d3a5d9b3c78 - std[60f4c921464387a8]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[f234d5aad18497a0]::util::run_in_thread_with_globals<rustc_interface[f234d5aad18497a0]::util::run_in_thread_pool_with_globals<rustc_interface[f234d5aad18497a0]::interface::run_compiler<(), rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  30:     0x7d3a5d9b395c - <<std[60f4c921464387a8]::thread::Builder>::spawn_unchecked_<rustc_interface[f234d5aad18497a0]::util::run_in_thread_with_globals<rustc_interface[f234d5aad18497a0]::util::run_in_thread_pool_with_globals<rustc_interface[f234d5aad18497a0]::interface::run_compiler<(), rustc_driver_impl[6e5208ea2b150886]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[494a681d6e07a62e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  31:     0x7d3a5d9b9e8d - std::sys::pal::unix::thread::Thread::new::thread_start::h0ed16f40fa4b751a
  32:     0x7d3a5748aaa4 - <unknown>
  33:     0x7d3a57517a34 - clone
  34:                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 `/playground/rustc-ice-2025-09-09T20_21_53-36.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [mir_borrowck] borrow-checking `TupleConst::{constant#0}`
#1 [analysis] running analysis passes on this crate
end of query stack