ICE: `invalid immediate for given destination place: scalar value has wrong size`

[matthiaskrgr]

auto-reduced (treereduce-rust):

trait Owner {
    const C<const N: u32>: u32 = N;
}

fn take0<const N: u64>(_: impl Owner<C<N> = { N }>) {}

fn main() {
    take0::<128>(());
}

impl Owner for () {
    ;
}

original:

trait Owner {
    const C<const N: u32>: u32 = N;
}

fn take0<const N: u64>(_: impl Owner<C<N> = { N }>) {}

fn main() {
    take0::<128>(());
}

impl Owner for () {
    const C<const N: u32>: u32 = N;
}

fn take0<const N: u64>(_: impl <128>) {}

fn main(_: impl Owner<C<N> = { N }>) {
    take0::<128>(());
}

Version information

rustc 1.83.0-nightly (6a3c45e1c 2024-10-08)
binary: rustc
commit-hash: 6a3c45e1c65e61b298fd6eaceac6d8ef4d973b66
commit-date: 2024-10-08
host: x86_64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.1

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

Program output

error: non-item in item list
  --> /tmp/icemaker_global_tempdir.2w6assLgpoXM/rustc_testrunner_tmpdir_reporting.CKpee9Fi7WqK/mvce.rs:12:5
   |
11 | impl Owner for () {
   |                   - item list starts here
12 |     ;
   |     ^ non-item starts here
13 | }
   | - item list ends here

error[E0658]: associated const equality is incomplete
 --> /tmp/icemaker_global_tempdir.2w6assLgpoXM/rustc_testrunner_tmpdir_reporting.CKpee9Fi7WqK/mvce.rs:5:38
  |
5 | fn take0<const N: u64>(_: impl Owner<C<N> = { N }>) {}
  |                                      ^^^^^^^^^^^^
  |
  = note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
  = help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
  = note: this compiler was built on 2024-10-08; consider upgrading it if it is out of date

error[E0658]: generic const items are experimental
 --> /tmp/icemaker_global_tempdir.2w6assLgpoXM/rustc_testrunner_tmpdir_reporting.CKpee9Fi7WqK/mvce.rs:2:12
  |
2 |     const C<const N: u32>: u32 = N;
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #113521 <https://github.com/rust-lang/rust/issues/113521> for more information
  = help: add `#![feature(generic_const_items)]` to the crate attributes to enable
  = note: this compiler was built on 2024-10-08; consider upgrading it if it is out of date

error: the constant `N` is not of type `u32`
 --> /tmp/icemaker_global_tempdir.2w6assLgpoXM/rustc_testrunner_tmpdir_reporting.CKpee9Fi7WqK/mvce.rs:5:38
  |
5 | fn take0<const N: u64>(_: impl Owner<C<N> = { N }>) {}
  |                                      ^^^^^^^^^^^^ expected `u32`, found `u64`
  |
note: required by a const generic parameter in `Owner::C`
 --> /tmp/icemaker_global_tempdir.2w6assLgpoXM/rustc_testrunner_tmpdir_reporting.CKpee9Fi7WqK/mvce.rs:2:13
  |
2 |     const C<const N: u32>: u32 = N;
  |             ^^^^^^^^^^^^ required by this const generic parameter in `Owner::C`

thread 'rustc' panicked at compiler/rustc_const_eval/src/interpret/operand.rs:119:17:
assertion `left == right` failed: invalid immediate for given destination place: scalar value has wrong size
  left: Size(8 bytes)
 right: Size(4 bytes)
stack backtrace:
   0:     0x7e41bbb3791a - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h3a851883c61e7981
   1:     0x7e41bc203466 - core::fmt::write::h71e264ea650e601d
   2:     0x7e41bd422b51 - std::io::Write::write_fmt::h627c59d250fe240c
   3:     0x7e41bbb37772 - std::sys::backtrace::BacktraceLock::print::h44906e04748e3e02
   4:     0x7e41bbb39c46 - std::panicking::default_hook::{{closure}}::he278d98c128c4a9d
   5:     0x7e41bbb39a90 - std::panicking::default_hook::h9cfc75667ebedffd
   6:     0x7e41babea8df - std[584ae1ac58580d89]::panicking::update_hook::<alloc[ea383159db73a253]::boxed::Box<rustc_driver_impl[6a0c09598ae9c08a]::install_ice_hook::{closure#0}>>::{closure#0}
   7:     0x7e41bbb3a358 - std::panicking::rust_panic_with_hook::hb2fe5d026efb466f
   8:     0x7e41bbb3a12a - std::panicking::begin_panic_handler::{{closure}}::h559274bc7def08cd
   9:     0x7e41bbb37dc9 - std::sys::backtrace::__rust_end_short_backtrace::hd9444e85474e39c0
  10:     0x7e41bbb39dec - rust_begin_unwind
  11:     0x7e41b94dbe70 - core::panicking::panic_fmt::h7d898ac73934d0c0
  12:     0x7e41ba5ed256 - core::panicking::assert_failed_inner::h3fd5e0c9c8a24468
  13:     0x7e41bab45cde - core[12ec0f185bbc53d2]::panicking::assert_failed::<rustc_abi[81e5ba8ae6f0eb2a]::Size, rustc_abi[81e5ba8ae6f0eb2a]::Size>
  14:     0x7e41bc998f01 - <rustc_const_eval[bcbc4c0dac6d4403]::interpret::eval_context::InterpCx<rustc_const_eval[bcbc4c0dac6d4403]::const_eval::machine::CompileTimeMachine>>::write_immediate_no_validate::<rustc_const_eval[bcbc4c0dac6d4403]::interpret::place::MPlaceTy>
  15:     0x7e41bc992a14 - <rustc_const_eval[bcbc4c0dac6d4403]::interpret::eval_context::InterpCx<rustc_const_eval[bcbc4c0dac6d4403]::const_eval::machine::CompileTimeMachine>>::return_from_current_stack_frame
  16:     0x7e41b9bdd4c9 - rustc_const_eval[bcbc4c0dac6d4403]::const_eval::eval_queries::eval_to_allocation_raw_provider
  17:     0x7e41bc9a1236 - rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::eval_to_allocation_raw::dynamic_query::{closure#2}::{closure#0}, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 24usize]>>
  18:     0x7e41bc9a0a5a - rustc_query_system[847c6ad2b9dd3ac1]::query::plumbing::try_execute_query::<rustc_query_impl[3daeaa2f12c0dbc5]::DynamicConfig<rustc_query_system[847c6ad2b9dd3ac1]::query::caches::DefaultCache<rustc_middle[6c2a42b363ada80b]::ty::ParamEnvAnd<rustc_middle[6c2a42b363ada80b]::mir::interpret::GlobalId>, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::QueryCtxt, false>
  19:     0x7e41bc9a062f - rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::eval_to_allocation_raw::get_query_non_incr::__rust_end_short_backtrace
  20:     0x7e41bc9ba6ab - rustc_const_eval[bcbc4c0dac6d4403]::const_eval::valtrees::eval_to_valtree
  21:     0x7e41bc9ba4bf - <rustc_const_eval[bcbc4c0dac6d4403]::provide::{closure#0} as core[12ec0f185bbc53d2]::ops::function::FnOnce<(rustc_middle[6c2a42b363ada80b]::ty::context::TyCtxt, rustc_middle[6c2a42b363ada80b]::ty::ParamEnvAnd<rustc_middle[6c2a42b363ada80b]::mir::interpret::GlobalId>)>>::call_once
  22:     0x7e41bc9ba476 - rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::eval_to_valtree::dynamic_query::{closure#2}::{closure#0}, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 24usize]>>
  23:     0x7e41bc9ba435 - <rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::eval_to_valtree::dynamic_query::{closure#2} as core[12ec0f185bbc53d2]::ops::function::FnOnce<(rustc_middle[6c2a42b363ada80b]::ty::context::TyCtxt, rustc_middle[6c2a42b363ada80b]::ty::ParamEnvAnd<rustc_middle[6c2a42b363ada80b]::mir::interpret::GlobalId>)>>::call_once
  24:     0x7e41bc9a0b2e - rustc_query_system[847c6ad2b9dd3ac1]::query::plumbing::try_execute_query::<rustc_query_impl[3daeaa2f12c0dbc5]::DynamicConfig<rustc_query_system[847c6ad2b9dd3ac1]::query::caches::DefaultCache<rustc_middle[6c2a42b363ada80b]::ty::ParamEnvAnd<rustc_middle[6c2a42b363ada80b]::mir::interpret::GlobalId>, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::QueryCtxt, false>
  25:     0x7e41bc9a044a - rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::eval_to_valtree::get_query_non_incr::__rust_end_short_backtrace
  26:     0x7e41bcc18437 - rustc_middle[6c2a42b363ada80b]::query::plumbing::query_get_at::<rustc_query_system[847c6ad2b9dd3ac1]::query::caches::DefaultCache<rustc_middle[6c2a42b363ada80b]::ty::ParamEnvAnd<rustc_middle[6c2a42b363ada80b]::mir::interpret::GlobalId>, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 24usize]>>>
  27:     0x7e41bcc17eaa - <rustc_middle[6c2a42b363ada80b]::ty::context::TyCtxt>::const_eval_global_id_for_typeck
  28:     0x7e41bcc16dbe - <rustc_middle[6c2a42b363ada80b]::ty::context::TyCtxt>::const_eval_resolve_for_typeck
  29:     0x7e41bcc16a05 - <rustc_middle[6c2a42b363ada80b]::ty::consts::Const>::normalize
  30:     0x7e41bcab6d26 - rustc_trait_selection[1c2265ed8fe6d14c]::traits::project::opt_normalize_projection_term
  31:     0x7e41bca9cfdc - rustc_trait_selection[1c2265ed8fe6d14c]::traits::project::poly_project_and_unify_term
  32:     0x7e41bc2662a8 - <rustc_trait_selection[1c2265ed8fe6d14c]::traits::select::SelectionContext>::evaluate_root_obligation
  33:     0x7e41bc264292 - rustc_traits[e9b239c6de819adf]::evaluate_obligation::evaluate_obligation
  34:     0x7e41bc263d29 - rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::evaluate_obligation::dynamic_query::{closure#2}::{closure#0}, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 2usize]>>
  35:     0x7e41bc2632d3 - rustc_query_system[847c6ad2b9dd3ac1]::query::plumbing::try_execute_query::<rustc_query_impl[3daeaa2f12c0dbc5]::DynamicConfig<rustc_query_system[847c6ad2b9dd3ac1]::query::caches::DefaultCache<rustc_type_ir[c34a23cd41056f95]::canonical::Canonical<rustc_middle[6c2a42b363ada80b]::ty::context::TyCtxt, rustc_middle[6c2a42b363ada80b]::ty::ParamEnvAnd<rustc_middle[6c2a42b363ada80b]::ty::predicate::Predicate>>, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 2usize]>>, false, false, false>, rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::QueryCtxt, false>
  36:     0x7e41bc262f24 - rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::evaluate_obligation::get_query_non_incr::__rust_end_short_backtrace
  37:     0x7e41b8a3c01e - <rustc_infer[a418d8929ad58d0a]::infer::InferCtxt as rustc_trait_selection[1c2265ed8fe6d14c]::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation_no_overflow
  38:     0x7e41b88c32b9 - <rustc_trait_selection[1c2265ed8fe6d14c]::traits::fulfill::FulfillProcessor>::process_projection_obligation
  39:     0x7e41b88ab544 - <rustc_trait_selection[1c2265ed8fe6d14c]::traits::fulfill::FulfillProcessor as rustc_data_structures[71eb2d5d27abd3bf]::obligation_forest::ObligationProcessor>::process_obligation
  40:     0x7e41bc20f112 - <rustc_data_structures[71eb2d5d27abd3bf]::obligation_forest::ObligationForest<rustc_trait_selection[1c2265ed8fe6d14c]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[1c2265ed8fe6d14c]::traits::fulfill::FulfillProcessor>
  41:     0x7e41b89d1939 - <rustc_hir_typeck[5f24e1131155eb7]::fn_ctxt::FnCtxt>::confirm_builtin_call
  42:     0x7e41bcea85cf - <rustc_hir_typeck[5f24e1131155eb7]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  43:     0x7e41bcea1a3e - <rustc_hir_typeck[5f24e1131155eb7]::fn_ctxt::FnCtxt>::check_block_with_expected
  44:     0x7e41bcea92e9 - <rustc_hir_typeck[5f24e1131155eb7]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  45:     0x7e41bc549ae1 - rustc_hir_typeck[5f24e1131155eb7]::check::check_fn
  46:     0x7e41bc53e861 - rustc_hir_typeck[5f24e1131155eb7]::typeck
  47:     0x7e41bc53e1cf - rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 8usize]>>
  48:     0x7e41bc64dfba - rustc_query_system[847c6ad2b9dd3ac1]::query::plumbing::try_execute_query::<rustc_query_impl[3daeaa2f12c0dbc5]::DynamicConfig<rustc_query_system[847c6ad2b9dd3ac1]::query::caches::VecCache<rustc_span[ff2bb122df6010f7]::def_id::LocalDefId, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::QueryCtxt, false>
  49:     0x7e41bc64cd1b - rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  50:     0x7e41bc64c9a1 - <rustc_middle[6c2a42b363ada80b]::hir::map::Map>::par_body_owners::<rustc_hir_analysis[944f64ea10dfd453]::check_crate::{closure#4}>::{closure#0}
  51:     0x7e41bc64a8db - rustc_hir_analysis[944f64ea10dfd453]::check_crate
  52:     0x7e41bc647317 - rustc_interface[6c180d597a38bbca]::passes::run_required_analyses
  53:     0x7e41bcf4b41e - rustc_interface[6c180d597a38bbca]::passes::analysis
  54:     0x7e41bcf4b3f1 - rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 1usize]>>
  55:     0x7e41bd1041ee - rustc_query_system[847c6ad2b9dd3ac1]::query::plumbing::try_execute_query::<rustc_query_impl[3daeaa2f12c0dbc5]::DynamicConfig<rustc_query_system[847c6ad2b9dd3ac1]::query::caches::SingleCache<rustc_middle[6c2a42b363ada80b]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[3daeaa2f12c0dbc5]::plumbing::QueryCtxt, false>
  56:     0x7e41bd103ecf - rustc_query_impl[3daeaa2f12c0dbc5]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  57:     0x7e41bcf610de - rustc_interface[6c180d597a38bbca]::interface::run_compiler::<core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>, rustc_driver_impl[6a0c09598ae9c08a]::run_compiler::{closure#0}>::{closure#1}
  58:     0x7e41bd00b790 - std[584ae1ac58580d89]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[6c180d597a38bbca]::util::run_in_thread_with_globals<rustc_interface[6c180d597a38bbca]::util::run_in_thread_pool_with_globals<rustc_interface[6c180d597a38bbca]::interface::run_compiler<core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>, rustc_driver_impl[6a0c09598ae9c08a]::run_compiler::{closure#0}>::{closure#1}, core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>>::{closure#0}, core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>>
  59:     0x7e41bd00be57 - <<std[584ae1ac58580d89]::thread::Builder>::spawn_unchecked_<rustc_interface[6c180d597a38bbca]::util::run_in_thread_with_globals<rustc_interface[6c180d597a38bbca]::util::run_in_thread_pool_with_globals<rustc_interface[6c180d597a38bbca]::interface::run_compiler<core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>, rustc_driver_impl[6a0c09598ae9c08a]::run_compiler::{closure#0}>::{closure#1}, core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>>::{closure#0}, core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[12ec0f185bbc53d2]::result::Result<(), rustc_span[ff2bb122df6010f7]::ErrorGuaranteed>>::{closure#1} as core[12ec0f185bbc53d2]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  60:     0x7e41bd00cd41 - std::sys::pal::unix::thread::Thread::new::thread_start::h54d489bd9073b86f
  61:     0x7e41be75139d - <unknown>
  62:     0x7e41be7d649c - <unknown>
  63:                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: rustc 1.83.0-nightly (6a3c45e1c 2024-10-08) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [eval_to_allocation_raw] const-evaluating + checking `Owner::C`
#1 [eval_to_valtree] evaluating type-level constant
end of query stack
error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0658`.

[matthiaskrgr]

this bisects to #129778 cc @RalfJung

[RalfJung]

impl Owner for () is missing the C item. How does any of this code ever get evaluated when it's not even syntactically well-formed, let alone well-typed?^^

Cc @BoxyUwU @lcnr
also Cc @oli-obk since tainting is likely involved again

[RalfJung]

Ah wait, that missing item is fine, it has a default.

The actual problem is here:

fn take0<const N: u64>(_: impl Owner<C<N> = { N }>) {}

N has type u64 but C expects a u32. It's not surprising that const-eval complains when you try to evaluate such a thing.

[BoxyUwU]

An example which only contains a type checking error:

#![feature(associated_const_equality, generic_const_items)]
#![allow(incomplete_features)]

trait Trait {
    const C<const N: u32>: u32;
}

impl Trait for () {
    const C<const N: u32>: u32 = N;
}

fn ice<const N: u64, T: Trait<C<N> = { N }>>(_: T) {}

fn main() {
    ice::<128, _>(());
}

[BoxyUwU]

When we type check main we wind up having to prove <() as Trait>::C<128_u64> = 128_u64 doing this requires normalizing <() as Trait>::C<128_u64>. Currently we do not check that consts are well formed before evaluating them (this caused issues in generic_const_exprs too, rust-lang/project-const-generics#37) so in attempting to get the normalized form of <() as Trait>::C<128_u64> we just invoke the ctfe machinery on a not-wf type system constant.