ICE: `expected const for .. but found Type(usize) when instantiating args=[usize] `

[matthiaskrgr]

snippet:

#![feature(generic_const_exprs)]

pub trait True {}

impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
    If<{}>: True
{
}

Version information

rustc 1.78.0-nightly (f8131a48a 2024-02-21)
binary: rustc
commit-hash: f8131a48a46ac3bc8a3d0fe0477055b132cffdc3
commit-date: 2024-02-21
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 18.1.0

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

Program output

error[E0412]: cannot find type `FixedI8` in this scope
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:50
  |
5 | impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                                                  ^^^^^^^ not found in this scope

error[E0412]: cannot find type `FRAC_RHS` in this scope
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:58
  |
5 | impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                                                          ^^^^^^^^ not found in this scope
  |
help: you might be missing a type parameter
  |
5 | impl<const N: usize = { const { 3 } }, FRAC_RHS> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                                      ++++++++++

error[E0412]: cannot find type `FixedI8` in this scope
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:73
  |
5 | impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                                                                         ^^^^^^^ not found in this scope

error[E0412]: cannot find type `FRAC_LHS` in this scope
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:81
  |
5 | impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                                                                                 ^^^^^^^^ not found in this scope
  |
help: you might be missing a type parameter
  |
5 | impl<const N: usize = { const { 3 } }, FRAC_LHS> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                                      ++++++++++

error[E0412]: cannot find type `If` in this scope
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:6:5
  |
6 |     If<{}>: True
  |     ^^ not found in this scope

error[E0658]: inline-const is experimental
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:25
  |
5 | impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |                         ^^^^^
  |
  = note: see issue #76001 <https://github.com/rust-lang/rust/issues/76001> for more information
  = help: add `#![feature(inline_const)]` to the crate attributes to enable
  = note: this compiler was built on 2024-02-21; consider upgrading it if it is out of date

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs: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

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:8:2
  |
8 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs`

error: defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
 --> /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:6
  |
5 | impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
  |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: compiler/rustc_middle/src/ty/generic_args.rs:956:9: expected const for `N/#0` (N/#0: usize/0) but found Type(usize) when instantiating args=[usize]

thread 'rustc' panicked at compiler/rustc_middle/src/util/bug.rs:35:44:
Box<dyn Any>
stack backtrace:
   0:     0x7ffa6ad8caf6 - std::backtrace_rs::backtrace::libunwind::trace::hbec2edc838b433e2
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7ffa6ad8caf6 - std::backtrace_rs::backtrace::trace_unsynchronized::h88c30257ee0dd166
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7ffa6ad8caf6 - std::sys_common::backtrace::_print_fmt::h9176654d509e3088
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7ffa6ad8caf6 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h671feaee1776bf19
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7ffa6addda7c - core::fmt::rt::Argument::fmt::h59605c83ae32d935
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/core/src/fmt/rt.rs:142:9
   5:     0x7ffa6addda7c - core::fmt::write::hf7af8dfcfd20db5b
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/core/src/fmt/mod.rs:1120:17
   6:     0x7ffa6ad814bf - std::io::Write::write_fmt::h92a5dbf489025e71
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/io/mod.rs:1846:15
   7:     0x7ffa6ad8c8a4 - std::sys_common::backtrace::_print::h00080302d23998ae
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7ffa6ad8c8a4 - std::sys_common::backtrace::print::h6b23124445400245
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7ffa6ad8f5eb - std::panicking::default_hook::{{closure}}::hd67b2f9d36675a28
  10:     0x7ffa6ad8f339 - std::panicking::default_hook::h10a39ef11c714e42
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/panicking.rs:292:9
  11:     0x7ffa6dc7a94c - std[5a8e7f94216a9138]::panicking::update_hook::<alloc[e14ab1f516d287ab]::boxed::Box<rustc_driver_impl[e279e4f1fedd9109]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7ffa6ad8fd50 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h37ba37dc48823c1d
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/alloc/src/boxed.rs:2030:9
  13:     0x7ffa6ad8fd50 - std::panicking::rust_panic_with_hook::he3e3bc7c345bf54b
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/panicking.rs:786:13
  14:     0x7ffa6dca7524 - std[5a8e7f94216a9138]::panicking::begin_panic::<rustc_errors[34364e5c712fab73]::ExplicitBug>::{closure#0}
  15:     0x7ffa6dca4176 - std[5a8e7f94216a9138]::sys_common::backtrace::__rust_end_short_backtrace::<std[5a8e7f94216a9138]::panicking::begin_panic<rustc_errors[34364e5c712fab73]::ExplicitBug>::{closure#0}, !>
  16:     0x7ffa6dc9f936 - std[5a8e7f94216a9138]::panicking::begin_panic::<rustc_errors[34364e5c712fab73]::ExplicitBug>
  17:     0x7ffa6c617631 - <rustc_errors[34364e5c712fab73]::diagnostic::BugAbort as rustc_errors[34364e5c712fab73]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  18:     0x7ffa6e08300c - <rustc_errors[34364e5c712fab73]::DiagCtxt>::bug::<alloc[e14ab1f516d287ab]::string::String>
  19:     0x7ffa6e127c7b - rustc_middle[446dd094ad85939e]::util::bug::opt_span_bug_fmt::<rustc_span[adb133ac03280fc1]::span_encoding::Span>::{closure#0}
  20:     0x7ffa6e10bc3a - rustc_middle[446dd094ad85939e]::ty::context::tls::with_opt::<rustc_middle[446dd094ad85939e]::util::bug::opt_span_bug_fmt<rustc_span[adb133ac03280fc1]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7ffa6e10bab8 - rustc_middle[446dd094ad85939e]::ty::context::tls::with_context_opt::<rustc_middle[446dd094ad85939e]::ty::context::tls::with_opt<rustc_middle[446dd094ad85939e]::util::bug::opt_span_bug_fmt<rustc_span[adb133ac03280fc1]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7ffa6c599af0 - rustc_middle[446dd094ad85939e]::util::bug::bug_fmt
  23:     0x7ffa6e11bba2 - <rustc_middle[446dd094ad85939e]::ty::generic_args::ArgFolder>::const_param_expected
  24:     0x7ffa6f038649 - <rustc_middle[446dd094ad85939e]::ty::generic_args::ArgFolder as rustc_type_ir[2405427f08dfadb1]::fold::TypeFolder<rustc_middle[446dd094ad85939e]::ty::context::TyCtxt>>::fold_const
  25:     0x7ffa6f37139d - <&rustc_middle[446dd094ad85939e]::ty::list::List<rustc_middle[446dd094ad85939e]::ty::generic_args::GenericArg> as rustc_type_ir[2405427f08dfadb1]::fold::TypeFoldable<rustc_middle[446dd094ad85939e]::ty::context::TyCtxt>>::try_fold_with::<rustc_middle[446dd094ad85939e]::ty::generic_args::ArgFolder>
  26:     0x7ffa6f038541 - <rustc_middle[446dd094ad85939e]::ty::generic_args::ArgFolder as rustc_type_ir[2405427f08dfadb1]::fold::TypeFolder<rustc_middle[446dd094ad85939e]::ty::context::TyCtxt>>::fold_const
  27:     0x7ffa6f037fc8 - <rustc_middle[446dd094ad85939e]::ty::predicate::Clause as rustc_type_ir[2405427f08dfadb1]::fold::TypeFoldable<rustc_middle[446dd094ad85939e]::ty::context::TyCtxt>>::try_fold_with::<rustc_middle[446dd094ad85939e]::ty::generic_args::ArgFolder>
  28:     0x7ffa6f035d60 - <rustc_middle[446dd094ad85939e]::ty::generics::GenericPredicates>::instantiate_into
  29:     0x7ffa6f035ff5 - <rustc_middle[446dd094ad85939e]::ty::generics::GenericPredicates>::instantiate_into
  30:     0x7ffa6f6aa74f - rustc_trait_selection[f311605eeacf2c8d]::traits::query::type_op::ascribe_user_type::type_op_ascribe_user_type_with_span
  31:     0x7ffa6f14fa91 - rustc_traits[e4f791f45ab3a736]::type_op::type_op_ascribe_user_type
  32:     0x7ffa6f14f42e - rustc_query_impl[9d4c51777e2bb749]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[9d4c51777e2bb749]::query_impl::type_op_ascribe_user_type::dynamic_query::{closure#2}::{closure#0}, rustc_middle[446dd094ad85939e]::query::erase::Erased<[u8; 8usize]>>
  33:     0x7ffa6f14f3f7 - <rustc_query_impl[9d4c51777e2bb749]::query_impl::type_op_ascribe_user_type::dynamic_query::{closure#2} as core[85b4fd477ce5bb21]::ops::function::FnOnce<(rustc_middle[446dd094ad85939e]::ty::context::TyCtxt, rustc_type_ir[2405427f08dfadb1]::canonical::Canonical<rustc_middle[446dd094ad85939e]::ty::context::TyCtxt, rustc_middle[446dd094ad85939e]::ty::ParamEnvAnd<rustc_middle[446dd094ad85939e]::traits::query::type_op::AscribeUserType>>)>>::call_once
  34:     0x7ffa6f9d0499 - rustc_query_system[9b2ccfe41ae3bb1b]::query::plumbing::try_execute_query::<rustc_query_impl[9d4c51777e2bb749]::DynamicConfig<rustc_query_system[9b2ccfe41ae3bb1b]::query::caches::DefaultCache<rustc_type_ir[2405427f08dfadb1]::canonical::Canonical<rustc_middle[446dd094ad85939e]::ty::context::TyCtxt, rustc_middle[446dd094ad85939e]::ty::ParamEnvAnd<rustc_middle[446dd094ad85939e]::traits::query::type_op::AscribeUserType>>, rustc_middle[446dd094ad85939e]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[9d4c51777e2bb749]::plumbing::QueryCtxt, false>
  35:     0x7ffa6f9d01ae - rustc_query_impl[9d4c51777e2bb749]::query_impl::type_op_ascribe_user_type::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7ffa6f9cff2d - <rustc_middle[446dd094ad85939e]::traits::query::type_op::AscribeUserType as rustc_trait_selection[f311605eeacf2c8d]::traits::query::type_op::QueryTypeOp>::perform_query
  37:     0x7ffa6fe65ce4 - <rustc_borrowck[bb9d4175d74ce943]::type_check::TypeChecker>::ascribe_user_type
  38:     0x7ffa6f5571b7 - <rustc_borrowck[bb9d4175d74ce943]::type_check::TypeVerifier as rustc_middle[446dd094ad85939e]::mir::visit::Visitor>::visit_operand
  39:     0x7ffa6cd3809f - <rustc_borrowck[bb9d4175d74ce943]::type_check::TypeVerifier as rustc_middle[446dd094ad85939e]::mir::visit::Visitor>::visit_body
  40:     0x7ffa6ccf2ae0 - rustc_borrowck[bb9d4175d74ce943]::type_check::type_check
  41:     0x7ffa6ccd96bc - rustc_borrowck[bb9d4175d74ce943]::nll::compute_regions
  42:     0x7ffa6fded246 - rustc_borrowck[bb9d4175d74ce943]::do_mir_borrowck
  43:     0x7ffa6fddfb40 - rustc_borrowck[bb9d4175d74ce943]::mir_borrowck
  44:     0x7ffa6fddf5d7 - rustc_query_impl[9d4c51777e2bb749]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[9d4c51777e2bb749]::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[446dd094ad85939e]::query::erase::Erased<[u8; 8usize]>>
  45:     0x7ffa6f1098b0 - rustc_query_system[9b2ccfe41ae3bb1b]::query::plumbing::try_execute_query::<rustc_query_impl[9d4c51777e2bb749]::DynamicConfig<rustc_query_system[9b2ccfe41ae3bb1b]::query::caches::VecCache<rustc_span[adb133ac03280fc1]::def_id::LocalDefId, rustc_middle[446dd094ad85939e]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[9d4c51777e2bb749]::plumbing::QueryCtxt, false>
  46:     0x7ffa6f10948c - rustc_query_impl[9d4c51777e2bb749]::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
  47:     0x7ffa6faa2f30 - rustc_interface[7ca501d7f8f3a34f]::passes::analysis
  48:     0x7ffa6faa2a29 - rustc_query_impl[9d4c51777e2bb749]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[9d4c51777e2bb749]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[446dd094ad85939e]::query::erase::Erased<[u8; 1usize]>>
  49:     0x7ffa6fd3d4a5 - rustc_query_system[9b2ccfe41ae3bb1b]::query::plumbing::try_execute_query::<rustc_query_impl[9d4c51777e2bb749]::DynamicConfig<rustc_query_system[9b2ccfe41ae3bb1b]::query::caches::SingleCache<rustc_middle[446dd094ad85939e]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[9d4c51777e2bb749]::plumbing::QueryCtxt, false>
  50:     0x7ffa6fd3d209 - rustc_query_impl[9d4c51777e2bb749]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  51:     0x7ffa6fd4c719 - rustc_interface[7ca501d7f8f3a34f]::interface::run_compiler::<core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>, rustc_driver_impl[e279e4f1fedd9109]::run_compiler::{closure#0}>::{closure#0}
  52:     0x7ffa6ffbe705 - std[5a8e7f94216a9138]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[7ca501d7f8f3a34f]::util::run_in_thread_with_globals<rustc_interface[7ca501d7f8f3a34f]::util::run_in_thread_pool_with_globals<rustc_interface[7ca501d7f8f3a34f]::interface::run_compiler<core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>, rustc_driver_impl[e279e4f1fedd9109]::run_compiler::{closure#0}>::{closure#0}, core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>>::{closure#0}, core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>>
  53:     0x7ffa6ffbe532 - <<std[5a8e7f94216a9138]::thread::Builder>::spawn_unchecked_<rustc_interface[7ca501d7f8f3a34f]::util::run_in_thread_with_globals<rustc_interface[7ca501d7f8f3a34f]::util::run_in_thread_pool_with_globals<rustc_interface[7ca501d7f8f3a34f]::interface::run_compiler<core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>, rustc_driver_impl[e279e4f1fedd9109]::run_compiler::{closure#0}>::{closure#0}, core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>>::{closure#0}, core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[85b4fd477ce5bb21]::result::Result<(), rustc_span[adb133ac03280fc1]::ErrorGuaranteed>>::{closure#1} as core[85b4fd477ce5bb21]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  54:     0x7ffa6ad99725 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h1bff3efb61c3fa6b
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/alloc/src/boxed.rs:2016:9
  55:     0x7ffa6ad99725 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h83141cf549dced8a
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/alloc/src/boxed.rs:2016:9
  56:     0x7ffa6ad99725 - std::sys::pal::unix::thread::Thread::new::thread_start::hbe9287fdd7c325bc
                               at /rustc/f8131a48a46ac3bc8a3d0fe0477055b132cffdc3/library/std/src/sys/pal/unix/thread.rs:108:17
  57:     0x7ffa6ab819eb - <unknown>
  58:     0x7ffa6ac057cc - <unknown>
  59:                0x0 - <unknown>

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: rustc 1.78.0-nightly (f8131a48a 2024-02-21) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [type_op_ascribe_user_type] evaluating `type_op_ascribe_user_type` `AscribeUserType { mir_ty: usize, user_ty: TypeOf(DefId(0:7 ~ mvce[8c01]::{impl#0}::{constant#0}::{constant#0}), UserArgs { args: [usize], user_self_ty: None }) }`
#1 [mir_borrowck] borrow-checking `<impl at /tmp/icemaker_global_tempdir.YLWanMEPxk5w/rustc_testrunner_tmpdir_reporting.GqWIEqxOTkdO/mvce.rs:5:1: 6:17>::{constant#0}`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 9 previous errors; 1 warning emitted

Some errors have detailed explanations: E0412, E0601, E0658.
For more information about an error, try `rustc --explain E0412`.

[matthiaskrgr]

#120847 cc @oli-obk

[camelid]

After #133610, this particular code no longer crashes, but adding definitions causes it to start crashing again:

//@ known-bug: #121429

#![feature(generic_const_exprs)]

struct FixedI8<const X: usize>;
const FRAC_LHS: usize = 0;
const FRAC_RHS: usize = 1;

pub trait True {}

impl<const N: usize = { const { 3 } }> PartialEq<FixedI8<FRAC_RHS>> for FixedI8<FRAC_LHS> where
    If<{}>: True
{
}