ICE: dyn_compatible_for_dispatch: `Got a scalar pair where a scalar was expected`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(dyn_compatible_for_dispatch)]
trait Qux {
    fn bar() -> i32;
}

pub struct Lint {
    pub desc: &'static dyn Qux,
}

static FOO: &Lint = &Lint { desc: "desc" };

original:

// This ensures we don't ICE in situations like rust-lang/rust#127299.

trait Qux {
    fn bar() -> i32;
}

pub struct Lint {
    pub desc: &'static dyn Qux,
    //~^ ERROR cannot be made into an object
}

static FOO: &Lint = &Lint { desc: "desc" };
//~^ ERROR cannot be shared between threads safely
//~| ERROR cannot be made into an object
//~| ERROR cannot be made into an object

fn main() {
        cur = cur.prev;
        test_vec.push(cur.data);
        if cur.head {
            break;
        }
    }

Version information

rustc 1.85.0-nightly (c528b8c67 2025-01-02)
binary: rustc
commit-hash: c528b8c67895bfe7fdcdfeb56ec5bf6ef928dcd7
commit-date: 2025-01-02
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

Possibly related line of code:

rust/compiler/rustc_const_eval/src/interpret/operand.rs

Lines 78 to 90 in c528b8c

	#[inline]
	#[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980)
	pub fn to_scalar(self) -> Scalar<Prov> {
	match self {
	Immediate::Scalar(val) => val,
	Immediate::ScalarPair(..) => bug!("Got a scalar pair where a scalar was expected"),
	Immediate::Uninit => bug!("Got uninit where a scalar was expected"),
	}
	}
	#[inline]
	#[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980)

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zcrate-attr=feature(dyn_compatible_for_dispatch)

Program output

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.3Xvq1QHsjJ49/rustc_testrunner_tmpdir_reporting.uMkbQerGsL7I/mvce.rs:9:44
  |
9 | static FOO: &Lint = &Lint { desc: "desc" };
  |                                            ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.3Xvq1QHsjJ49/rustc_testrunner_tmpdir_reporting.uMkbQerGsL7I/mvce.rs`

error[E0277]: `(dyn Qux + 'static)` cannot be shared between threads safely
 --> /tmp/icemaker_global_tempdir.3Xvq1QHsjJ49/rustc_testrunner_tmpdir_reporting.uMkbQerGsL7I/mvce.rs:9:13
  |
9 | static FOO: &Lint = &Lint { desc: "desc" };
  |             ^^^^^ `(dyn Qux + 'static)` cannot be shared between threads safely
  |
  = help: within `&'static Lint`, the trait `Sync` is not implemented for `(dyn Qux + 'static)`
  = note: required because it appears within the type `&'static (dyn Qux + 'static)`
note: required because it appears within the type `Lint`
 --> /tmp/icemaker_global_tempdir.3Xvq1QHsjJ49/rustc_testrunner_tmpdir_reporting.uMkbQerGsL7I/mvce.rs:5:12
  |
5 | pub struct Lint {
  |            ^^^^
  = note: required because it appears within the type `&'static Lint`
  = note: shared static variables must have a type that implements `Sync`

error[E0038]: the trait `Qux` cannot be made into an object
 --> /tmp/icemaker_global_tempdir.3Xvq1QHsjJ49/rustc_testrunner_tmpdir_reporting.uMkbQerGsL7I/mvce.rs:9:35
  |
9 | static FOO: &Lint = &Lint { desc: "desc" };
  |                                   ^^^^^^ `Qux` cannot be made into an object
  |
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
 --> /tmp/icemaker_global_tempdir.3Xvq1QHsjJ49/rustc_testrunner_tmpdir_reporting.uMkbQerGsL7I/mvce.rs:2:8
  |
1 | trait Qux {
  |       --- this trait cannot be made into an object...
2 |     fn bar() -> i32;
  |        ^^^ ...because associated function `bar` has no `self` parameter
  = note: required for the cast from `&'static str` to `&'static (dyn Qux + 'static)`
help: consider turning `bar` into a method by giving it a `&self` argument
  |
2 |     fn bar(&self) -> i32;
  |            +++++
help: alternatively, consider constraining `bar` so it does not apply to trait objects
  |
2 |     fn bar() -> i32 where Self: Sized;
  |                     +++++++++++++++++

error: internal compiler error: compiler/rustc_const_eval/src/interpret/operand.rs:84:42: Got a scalar pair where a scalar was expected

thread 'rustc' panicked at compiler/rustc_const_eval/src/interpret/operand.rs:84:42:
Box<dyn Any>
stack backtrace:
   0:     0x7a0e616d51ba - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h2b8b9078b210113e
   1:     0x7a0e61e13426 - core::fmt::write::hdcc55b58dc0c6e20
   2:     0x7a0e62d33551 - std::io::Write::write_fmt::h7c213661509c402d
   3:     0x7a0e616d5012 - std::sys::backtrace::BacktraceLock::print::hdb143750fa5d59cd
   4:     0x7a0e616d7519 - std::panicking::default_hook::{{closure}}::hf2cb20f74db395d1
   5:     0x7a0e616d7362 - std::panicking::default_hook::h86d0bfbfd5bce384
   6:     0x7a0e60846708 - std[ee56002db93e12e2]::panicking::update_hook::<alloc[b23fc7866e8473ce]::boxed::Box<rustc_driver_impl[18d794ab20952b7]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7a0e616d7cd3 - std::panicking::rust_panic_with_hook::h34871acc4888ae97
   8:     0x7a0e6087ea21 - std[ee56002db93e12e2]::panicking::begin_panic::<rustc_errors[d3d60be57c523ca2]::ExplicitBug>::{closure#0}
   9:     0x7a0e60873c06 - std[ee56002db93e12e2]::sys::backtrace::__rust_end_short_backtrace::<std[ee56002db93e12e2]::panicking::begin_panic<rustc_errors[d3d60be57c523ca2]::ExplicitBug>::{closure#0}, !>
  10:     0x7a0e60873bef - std[ee56002db93e12e2]::panicking::begin_panic::<rustc_errors[d3d60be57c523ca2]::ExplicitBug>
  11:     0x7a0e60888981 - <rustc_errors[d3d60be57c523ca2]::diagnostic::BugAbort as rustc_errors[d3d60be57c523ca2]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x7a0e60e67dc3 - rustc_middle[afd76c1e2fa1f4aa]::util::bug::opt_span_bug_fmt::<rustc_span[192a0d4408a1863b]::span_encoding::Span>::{closure#0}
  13:     0x7a0e60e4ce6a - rustc_middle[afd76c1e2fa1f4aa]::ty::context::tls::with_opt::<rustc_middle[afd76c1e2fa1f4aa]::util::bug::opt_span_bug_fmt<rustc_span[192a0d4408a1863b]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7a0e60e4ccfb - rustc_middle[afd76c1e2fa1f4aa]::ty::context::tls::with_context_opt::<rustc_middle[afd76c1e2fa1f4aa]::ty::context::tls::with_opt<rustc_middle[afd76c1e2fa1f4aa]::util::bug::opt_span_bug_fmt<rustc_span[192a0d4408a1863b]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7a0e5f1afd80 - rustc_middle[afd76c1e2fa1f4aa]::util::bug::bug_fmt
  16:     0x7a0e6335fda7 - <rustc_const_eval[de8e8d1f69cd5ad7]::interpret::eval_context::InterpCx<rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::machine::CompileTimeMachine>>::read_pointer::<rustc_const_eval[de8e8d1f69cd5ad7]::interpret::operand::OpTy>.cold
  17:     0x7a0e61ef2876 - <rustc_const_eval[de8e8d1f69cd5ad7]::interpret::eval_context::InterpCx<rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::machine::CompileTimeMachine>>::unsize_into_ptr
  18:     0x7a0e62990c72 - <rustc_const_eval[de8e8d1f69cd5ad7]::interpret::eval_context::InterpCx<rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::machine::CompileTimeMachine>>::eval_rvalue_into_place
  19:     0x7a0e5fc6f4bd - rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::eval_queries::eval_to_allocation_raw_provider
  20:     0x7a0e625cd3be - rustc_query_impl[8926239a3dc5fb5d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_to_allocation_raw::dynamic_query::{closure#2}::{closure#0}, rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 24usize]>>
  21:     0x7a0e625cccec - rustc_query_system[8fc0a43a0b6251a8]::query::plumbing::try_execute_query::<rustc_query_impl[8926239a3dc5fb5d]::DynamicConfig<rustc_query_system[8fc0a43a0b6251a8]::query::caches::DefaultCache<rustc_middle[afd76c1e2fa1f4aa]::ty::PseudoCanonicalInput<rustc_middle[afd76c1e2fa1f4aa]::mir::interpret::GlobalId>, rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[8926239a3dc5fb5d]::plumbing::QueryCtxt, false>
  22:     0x7a0e625cc84d - rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_to_allocation_raw::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7a0e625ca3f7 - rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::eval_queries::eval_to_const_value_raw_provider
  24:     0x7a0e625ca200 - rustc_query_impl[8926239a3dc5fb5d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_to_const_value_raw::dynamic_query::{closure#2}::{closure#0}, rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 24usize]>>
  25:     0x7a0e625ccca3 - rustc_query_system[8fc0a43a0b6251a8]::query::plumbing::try_execute_query::<rustc_query_impl[8926239a3dc5fb5d]::DynamicConfig<rustc_query_system[8fc0a43a0b6251a8]::query::caches::DefaultCache<rustc_middle[afd76c1e2fa1f4aa]::ty::PseudoCanonicalInput<rustc_middle[afd76c1e2fa1f4aa]::mir::interpret::GlobalId>, rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[8926239a3dc5fb5d]::plumbing::QueryCtxt, false>
  26:     0x7a0e625cc755 - rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_to_const_value_raw::get_query_non_incr::__rust_end_short_backtrace
  27:     0x7a0e61ef9da6 - <rustc_middle[afd76c1e2fa1f4aa]::ty::context::TyCtxt>::const_eval_resolve
  28:     0x7a0e631513d4 - rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::eval_queries::eval_body_using_ecx::<rustc_middle[afd76c1e2fa1f4aa]::mir::interpret::allocation::ConstAllocation>
  29:     0x7a0e6314bd3d - rustc_const_eval[de8e8d1f69cd5ad7]::const_eval::eval_queries::eval_static_initializer_provider
  30:     0x7a0e6314bae7 - rustc_query_impl[8926239a3dc5fb5d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_static_initializer::dynamic_query::{closure#2}::{closure#0}, rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 16usize]>>
  31:     0x7a0e6314bac9 - <rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_static_initializer::dynamic_query::{closure#2} as core[d5539697cc88e8d8]::ops::function::FnOnce<(rustc_middle[afd76c1e2fa1f4aa]::ty::context::TyCtxt, rustc_span[192a0d4408a1863b]::def_id::DefId)>>::call_once
  32:     0x7a0e6203f78a - rustc_query_system[8fc0a43a0b6251a8]::query::plumbing::try_execute_query::<rustc_query_impl[8926239a3dc5fb5d]::DynamicConfig<rustc_query_system[8fc0a43a0b6251a8]::query::caches::DefIdCache<rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[8926239a3dc5fb5d]::plumbing::QueryCtxt, false>
  33:     0x7a0e62d8d6b8 - rustc_query_impl[8926239a3dc5fb5d]::query_impl::eval_static_initializer::get_query_non_incr::__rust_end_short_backtrace
  34:     0x7a0e620fbf4d - <rustc_middle[afd76c1e2fa1f4aa]::hir::map::Map>::par_body_owners::<rustc_hir_analysis[8a14451cc762fcb8]::check_crate::{closure#3}>::{closure#0}
  35:     0x7a0e620f98a5 - rustc_hir_analysis[8a14451cc762fcb8]::check_crate
  36:     0x7a0e622700e8 - rustc_interface[b9625d7f43db6951]::passes::run_required_analyses
  37:     0x7a0e62d472de - rustc_interface[b9625d7f43db6951]::passes::analysis
  38:     0x7a0e62d472af - rustc_query_impl[8926239a3dc5fb5d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[8926239a3dc5fb5d]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 0usize]>>
  39:     0x7a0e62d92055 - rustc_query_system[8fc0a43a0b6251a8]::query::plumbing::try_execute_query::<rustc_query_impl[8926239a3dc5fb5d]::DynamicConfig<rustc_query_system[8fc0a43a0b6251a8]::query::caches::SingleCache<rustc_middle[afd76c1e2fa1f4aa]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[8926239a3dc5fb5d]::plumbing::QueryCtxt, false>
  40:     0x7a0e62d91d8e - rustc_query_impl[8926239a3dc5fb5d]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  41:     0x7a0e62e0091e - rustc_interface[b9625d7f43db6951]::passes::create_and_enter_global_ctxt::<core[d5539697cc88e8d8]::option::Option<rustc_interface[b9625d7f43db6951]::queries::Linker>, rustc_driver_impl[18d794ab20952b7]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  42:     0x7a0e62dd5ca4 - rustc_interface[b9625d7f43db6951]::interface::run_compiler::<(), rustc_driver_impl[18d794ab20952b7]::run_compiler::{closure#0}>::{closure#1}
  43:     0x7a0e62c65891 - std[ee56002db93e12e2]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[b9625d7f43db6951]::util::run_in_thread_with_globals<rustc_interface[b9625d7f43db6951]::util::run_in_thread_pool_with_globals<rustc_interface[b9625d7f43db6951]::interface::run_compiler<(), rustc_driver_impl[18d794ab20952b7]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  44:     0x7a0e62c65d48 - <<std[ee56002db93e12e2]::thread::Builder>::spawn_unchecked_<rustc_interface[b9625d7f43db6951]::util::run_in_thread_with_globals<rustc_interface[b9625d7f43db6951]::util::run_in_thread_pool_with_globals<rustc_interface[b9625d7f43db6951]::interface::run_compiler<(), rustc_driver_impl[18d794ab20952b7]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[d5539697cc88e8d8]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  45:     0x7a0e62c67301 - std::sys::pal::unix::thread::Thread::new::thread_start::h8be4dfe5558d2b77
  46:     0x7a0e5d0a339d - <unknown>
  47:     0x7a0e5d12849c - <unknown>
  48:                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: please make sure that you have updated to the latest nightly

note: rustc 1.85.0-nightly (c528b8c67 2025-01-02) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z crate-attr=feature(dyn_compatible_for_dispatch) -Z dump-mir-dir=dir

query stack during panic:
#0 [eval_to_allocation_raw] const-evaluating + checking `FOO::promoted[0]`
#1 [eval_to_const_value_raw] simplifying constant for the type system `FOO::promoted[0]`
#2 [eval_static_initializer] evaluating initializer of static `FOO`
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 4 previous errors

Some errors have detailed explanations: E0038, E0277, E0601.
For more information about an error, try `rustc --explain E0038`.

@rustbot label +F-dyn_compatible_for_dispatch

[matthiaskrgr]

Regression in nightly-2024-07-02
commit[0] 2024-06-30: Auto merge of #127174 - matthiaskrgr:rollup-q87j6cn, r=matthiaskrgr
commit[1] 2024-06-30: Auto merge of #127026 - Urgau:cleanup-bootstrap-check-cfg, r=Kobzol
commit[2] 2024-07-01: Auto merge of #127082 - GuillaumeGomez:help-gui-test, r=notriddle
commit[3] 2024-07-01: Auto merge of #127176 - fee1-dead-contrib:fx-requires-next-solver, r=compiler-errors
commit[4] 2024-07-01: Auto merge of #126996 - oli-obk:do_not_count_errors, r=nnethercote
commit[5] 2024-07-01: Auto merge of #127197 - matthiaskrgr:rollup-aqpvn5q, r=matthiaskrgr
commit[6] 2024-07-01: Auto merge of #127113 - scottmcm:retune-inlining-again, r=oli-obk
commit[7] 2024-07-01: Auto merge of #127216 - GuillaumeGomez:rollup-iw9f2ed, r=GuillaumeGomez

[cyrgani]

smaller:

#![feature(dyn_compatible_for_dispatch)]
trait Qux {
    fn bar();
}

static FOO: &'static dyn Qux = "desc";