ICE: lazy_type_alias: cannot relate consts of different types

[matthiaskrgr]

Code

#![feature(adt_const_params, lazy_type_alias)]

pub type Matrix = [usize; 1];
const EMPTY_MATRIX: Matrix = [0; 1];

pub struct Walk<const REMAINING: Matrix> {}

impl Walk<EMPTY_MATRIX> {
    pub const fn new() -> Self {
        Self {}
    }
}

fn main() {
    let _ = Walk::new();
}

Meta

rustc --version --verbose:

rustc 1.73.0-nightly (474709a9a 2023-08-03)
binary: rustc
commit-hash: 474709a9a2a74a8bcf0055fadb335d0ca0d2d939
commit-date: 2023-08-03
host: x86_64-unknown-linux-gnu
release: 1.73.0-nightly
LLVM version: 16.0.5

Error output

<output>

Backtrace

warning: the feature `adt_const_params` is incomplete and may not be safe to use and/or cause compiler crashes
 --> treereduce.out:1:12
  |
1 | #![feature(adt_const_params, lazy_type_alias)]
  |            ^^^^^^^^^^^^^^^^
  |
  = note: see issue #95174 <https://github.com/rust-lang/rust/issues/95174> for more information
  = note: `#[warn(incomplete_features)]` on by default

warning: the feature `lazy_type_alias` is incomplete and may not be safe to use and/or cause compiler crashes
 --> treereduce.out:1:30
  |
1 | #![feature(adt_const_params, lazy_type_alias)]
  |                              ^^^^^^^^^^^^^^^
  |
  = note: see issue #112792 <https://github.com/rust-lang/rust/issues/112792> for more information

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: cannot relate consts of different types (a=Const { ty: Matrix, kind: ?0c }, b=Const { ty: [usize; 1], kind: Branch([Leaf(0x0000000000000000)]) })
  |
  = note: delayed at /rustc/474709a9a2a74a8bcf0055fadb335d0ca0d2d939/compiler/rustc_infer/src/infer/combine.rs:178:31
             0: <rustc_errors::HandlerInner>::emit_diagnostic
             1: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, alloc::string::String>
             2: <rustc_infer::infer::InferCtxt>::super_combine_consts::<rustc_infer::infer::nll_relate::TypeRelating<rustc_infer::infer::canonical::query_response::QueryTypeRelatingDelegate>>
             3: <rustc_infer::infer::nll_relate::TypeRelating<rustc_infer::infer::canonical::query_response::QueryTypeRelatingDelegate> as rustc_middle::ty::relate::TypeRelation>::consts
             4: <rustc_infer::infer::InferCtxt>::instantiate_nll_query_response_and_region_obligations::<()>
             5: <rustc_middle::ty::ParamEnvAnd<rustc_middle::traits::query::type_op::AscribeUserType> as rustc_trait_selection::traits::query::type_op::TypeOp>::fully_perform
             6: <rustc_borrowck::type_check::TypeChecker>::ascribe_user_type
             7: rustc_borrowck::type_check::type_check
             8: rustc_borrowck::nll::compute_regions
             9: rustc_borrowck::do_mir_borrowck
            10: rustc_borrowck::mir_borrowck
            11: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
            12: <rustc_query_impl::query_impl::mir_borrowck::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
            13: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            14: rustc_query_impl::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
            15: rustc_data_structures::sync::par_for_each_in::<&[rustc_span::def_id::LocalDefId], <rustc_middle::hir::map::Map>::par_body_owners<rustc_interface::passes::analysis::{closure#1}::{closure#0}>::{closure#0}>
            16: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#1}>
            17: rustc_interface::passes::analysis
            18: 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; 1]>>
            19: <rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, ())>>::call_once
            20: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            21: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
            22: <rustc_middle::ty::context::GlobalCtxt>::enter::<rustc_driver_impl::run_compiler::{closure#1}::{closure#2}::{closure#4}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
            23: <rustc_interface::interface::Compiler>::enter::<rustc_driver_impl::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_span::ErrorGuaranteed>>
            24: std::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
            25: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
            26: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/474709a9a2a74a8bcf0055fadb335d0ca0d2d939/library/alloc/src/boxed.rs:2007:9
            27: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/474709a9a2a74a8bcf0055fadb335d0ca0d2d939/library/alloc/src/boxed.rs:2007:9
            28: std::sys::unix::thread::Thread::new::thread_start
                       at /rustc/474709a9a2a74a8bcf0055fadb335d0ca0d2d939/library/std/src/sys/unix/thread.rs:108:17
            29: <unknown>
            30: <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: please attach the file at `/tmp/im/rustc-ice-2023-08-04T10:13:31.528732612Z-1012286.txt` to your bug report

query stack during panic:
end of query stack
error: aborting due to 2 previous errors; 2 warnings emitted

[matthiaskrgr]

bisected to introduction in #112853

[fmease]

Lazy type aliases are not necessary to reproduce this:

#![feature(adt_const_params)]

const EMPTY_MATRIX: <Type as Trait>::Matrix = [0; 1];

pub struct Walk<const REMAINING: <Type as Trait>::Matrix> {}

impl Walk<EMPTY_MATRIX> {
    pub const fn new() -> Self {
        Self {}
    }
}

pub enum Type {}
pub trait Trait { type Matrix; }
impl Trait for Type { type Matrix = [usize; 1]; }

fn main() {
    let _ = Walk::new();
}

[fmease]

I'd like to clarify, we should definitely keep the label F-lazy_type_alias since this code will regress if / once we make lazy type aliases the default (in a new edition). However, my finding demonstrates that the bug is preexisting. The faulty code path doesn't handle alias types (ty::AliasTy) correctly (ty::Projection in the case of associated types and ty::Weak in the case of lazy type aliases).

@rustbot label -needs-triage