ICE when creating a reference to an (extern?) value of an extern type in a static context

[CheaterCodes]

Also on Rust Playground:
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=5602ca55d70c4f28705a4740310228f4

Code

#![feature(extern_types)]

extern {
    pub type ExternType;
}

extern "C" {
    pub static EXTERN: ExternType;
}

pub static EMPTY: () = unsafe { &EXTERN; };

fn main() {}

Meta

rustc --version --verbose:

rustc 1.67.0-nightly (a28f3c88e 2022-11-20)
binary: rustc
commit-hash: a28f3c88e50a77bc2a91889241248c4543854e61
commit-date: 2022-11-20
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly
LLVM version: 15.0.4

Error output

thread '<unnamed>' panicked at 'assertion failed: layout.is_sized()', compiler/rustc_const_eval/src/interpret/memory.rs:685:17

Backtrace

   0: rust_begin_unwind
             at /rustc/a28f3c88e50a77bc2a91889241248c4543854e61/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/a28f3c88e50a77bc2a91889241248c4543854e61/library/core/src/panicking.rs:65:14
   2: core::panicking::panic
             at /rustc/a28f3c88e50a77bc2a91889241248c4543854e61/library/core/src/panicking.rs:114:5
   3: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeInterpreter>>::run
   4: rustc_const_eval::const_eval::eval_queries::eval_to_allocation_raw_provider
   5: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::ParamEnvAnd<rustc_middle::mir::interpret::GlobalId>, core::result::Result<rustc_middle::mir::interpret::value::ConstAlloc, rustc_middle::mir::interpret::error::ErrorHandled>>>
   6: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::eval_to_allocation_raw
   7: rustc_const_eval::const_eval::eval_queries::eval_to_allocation_raw_provider
   8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::ParamEnvAnd<rustc_middle::mir::interpret::GlobalId>, core::result::Result<rustc_middle::mir::interpret::value::ConstAlloc, rustc_middle::mir::interpret::error::ErrorHandled>>>
   9: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::eval_to_allocation_raw
  10: <rustc_middle::ty::query::TyCtxtEnsure>::eval_static_initializer
  11: <rustc_lint::BuiltinCombinedModuleLateLintPass as rustc_lint::passes::LateLintPass>::check_item
  12: rustc_hir::intravisit::walk_mod::<rustc_lint::late::LateContextAndPass<rustc_lint::BuiltinCombinedModuleLateLintPass>>
  13: rustc_lint::late::late_lint_mod::<rustc_lint::BuiltinCombinedModuleLateLintPass>
  14: rustc_lint::lint_mod
  15: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, ()>>
  16: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::lint_mod, rustc_query_impl::plumbing::QueryCtxt>
  17: rustc_data_structures::sync::par_for_each_in::<&[rustc_hir::hir_id::OwnerId], <rustc_middle::hir::map::Map>::par_for_each_module<rustc_lint::late::check_crate<rustc_lint::BuiltinCombinedLateLintPass, rustc_interface::passes::analysis::{closure#5}::{closure#1}::{closure#2}::{closure#0}::{closure#0}>::{closure#1}::{closure#0}::{closure#0}>::{closure#0}>
  18: <rustc_session::session::Session>::time::<(), rustc_lint::late::check_crate<rustc_lint::BuiltinCombinedLateLintPass, rustc_interface::passes::analysis::{closure#5}::{closure#1}::{closure#2}::{closure#0}::{closure#0}>::{closure#1}::{closure#0}>
  19: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#5}::{closure#1}::{closure#2}::{closure#0}>
  20: <core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::passes::analysis::{closure#5}::{closure#1}> as core::ops::function::FnOnce<()>>::call_once
  21: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#5}>
  22: rustc_interface::passes::analysis
  23: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), core::result::Result<(), rustc_errors::ErrorGuaranteed>>>
  24: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
  25: <rustc_interface::passes::QueryContext>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}::{closure#3}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
  26: <rustc_interface::interface::Compiler>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_errors::ErrorGuaranteed>>
  27: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}::{closure#1}>
  28: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>

[riking]

Note that the static EMPTY takes the reference and then tosses it out.

[CheaterCodes]

I originally encountered this when casting the reference to a pointer and then storing it in a static (via a wrapper), but since this wasn't needed for the crash, I simplified the example.
Also just to mention it: This obviously doesn't happen when using e.g. u8 instead of ExternType.

[CheaterCodes]

This appears to be fixed in current nightly, so I think this can be closed

[matthiaskrgr]

This still crashes with -Zextra-const-ub-checks cc @RalfJung maybe?

[RalfJung]

Should we really allow extern static of unsized types? I don't think we should, that makes fairly little sense to me.

Note that we reject this:

extern "C" {
    pub static EXTERN: [i32];
}

saying

error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
 --> src/main.rs:2:24
  |
2 |     pub static EXTERN: [i32];
  |                        ^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `Sized` is not implemented for `[i32]`

we should make the same error show up for extern types. This is just a bug somewhere in the (unstable) extern type feature.