ICE: Failed to resolve instance for `<() as Supertrait<()>>::method`

[matthiaskrgr]

auto-reduced (treereduce-rust):

//@compile-flags: -Zmir-opt-level=5 -Zvalidate-mir
trait Supertrait<T> {
    fn method(&self) {}
}

trait Trait<P>: Supertrait<()> {}

impl<P> Trait<P> for () {}

fn upcast<P>(x: &dyn Trait<P>) -> &dyn Supertrait<()> {
    x
}

fn main() {
    upcast::<()>(&()).method();
}

original:

#![feature(trait_upcasting)]

trait Supertrait<T> {
    fn method(&self) {}
}
impl<T> Supertrait<T> for () {}

trait Identity {
    type Selff;
}
impl NonZeroF64 {
    pub fn new(_: f64) -> Option<Self> {
        None
    }
}
trait Trait<P>: Supertrait<()> + Supertrait<<P as Identity>::Selff> {}

impl<P> Trait<P> for () {}

fn upcast<P>(x: &dyn Trait<P>) -> &dyn Supertrait<()> {
    x
}

fn main() {
    upcast::<()>(&()).method();
}

Version information

rustc 1.87.0-nightly (ce36a966c 2025-02-17)
binary: rustc
commit-hash: ce36a966c79e109dabeef7a47fe68e5294c6d71e
commit-date: 2025-02-17
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Possibly related line of code:

rust/compiler/rustc_middle/src/ty/instance.rs

Lines 597 to 609 in ce36a96

	shrunk,
	was_written,
	path,
	type_length,
	});
	} else {
	span_bug!(
	span_or_local_def_span(),
	"failed to resolve instance for {}",
	tcx.def_path_str_with_args(def_id, args)
	)
	}
	}

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zmir-opt-level=5 -Zvalidate-mir

Program output

error[E0277]: the trait bound `(): Supertrait<()>` is not satisfied
 --> /tmp/icemaker_global_tempdir.qxoy71AFuMEA/rustc_testrunner_tmpdir_reporting.SjuyEgDtsyCA/mvce.rs:7:22
  |
7 | impl<P> Trait<P> for () {}
  |                      ^^ the trait `Supertrait<()>` is not implemented for `()`
  |
help: this trait has no implementations, consider adding one
 --> /tmp/icemaker_global_tempdir.qxoy71AFuMEA/rustc_testrunner_tmpdir_reporting.SjuyEgDtsyCA/mvce.rs:1:1
  |
1 | trait Supertrait<T> {
  | ^^^^^^^^^^^^^^^^^^^
note: required by a bound in `Trait`
 --> /tmp/icemaker_global_tempdir.qxoy71AFuMEA/rustc_testrunner_tmpdir_reporting.SjuyEgDtsyCA/mvce.rs:5:17
  |
5 | trait Trait<P>: Supertrait<()> {}
  |                 ^^^^^^^^^^^^^^ required by this bound in `Trait`

error: internal compiler error: compiler/rustc_middle/src/ty/instance.rs:603:21: failed to resolve instance for <() as Supertrait<()>>::method
 --> /tmp/icemaker_global_tempdir.qxoy71AFuMEA/rustc_testrunner_tmpdir_reporting.SjuyEgDtsyCA/mvce.rs:2:5
  |
2 |     fn method(&self) {}
  |     ^^^^^^^^^^^^^^^^


thread 'rustc' panicked at compiler/rustc_middle/src/ty/instance.rs:603:21:
Box<dyn Any>
stack backtrace:
   0:     0x77994b199e40 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h3841cd57ff2ecd73
   1:     0x77994ba148ac - core::fmt::write::h1e3520bf56740af3
   2:     0x77994ca318d1 - std::io::Write::write_fmt::hba9e4167b3001b26
   3:     0x77994b199ca2 - std::sys::backtrace::BacktraceLock::print::h4cef63a231b9b903
   4:     0x77994b19c4a6 - std::panicking::default_hook::{{closure}}::h42a071c1742d1486
   5:     0x77994b19c084 - std::panicking::default_hook::hb623603f8ca8d5a9
   6:     0x77994a2e571b - std[3b75b760e1909bee]::panicking::update_hook::<alloc[fee51eceb6acdb2a]::boxed::Box<rustc_driver_impl[345723d7f8fea549]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x77994b19cd53 - std::panicking::rust_panic_with_hook::h4a78a56a08a0281e
   8:     0x77994a3218a1 - std[3b75b760e1909bee]::panicking::begin_panic::<rustc_errors[ebdc752efb94ef64]::ExplicitBug>::{closure#0}
   9:     0x77994a315c86 - std[3b75b760e1909bee]::sys::backtrace::__rust_end_short_backtrace::<std[3b75b760e1909bee]::panicking::begin_panic<rustc_errors[ebdc752efb94ef64]::ExplicitBug>::{closure#0}, !>
  10:     0x77994a315a67 - std[3b75b760e1909bee]::panicking::begin_panic::<rustc_errors[ebdc752efb94ef64]::ExplicitBug>
  11:     0x77994a32b241 - <rustc_errors[ebdc752efb94ef64]::diagnostic::BugAbort as rustc_errors[ebdc752efb94ef64]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x77994a87874c - <rustc_errors[ebdc752efb94ef64]::DiagCtxtHandle>::span_bug::<rustc_span[75e5c439b5acee8]::span_encoding::Span, alloc[fee51eceb6acdb2a]::string::String>
  13:     0x77994a8f8477 - rustc_middle[8f0bb18145f914db]::util::bug::opt_span_bug_fmt::<rustc_span[75e5c439b5acee8]::span_encoding::Span>::{closure#0}
  14:     0x77994a8e16da - rustc_middle[8f0bb18145f914db]::ty::context::tls::with_opt::<rustc_middle[8f0bb18145f914db]::util::bug::opt_span_bug_fmt<rustc_span[75e5c439b5acee8]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  15:     0x77994a8e156b - rustc_middle[8f0bb18145f914db]::ty::context::tls::with_context_opt::<rustc_middle[8f0bb18145f914db]::ty::context::tls::with_opt<rustc_middle[8f0bb18145f914db]::util::bug::opt_span_bug_fmt<rustc_span[75e5c439b5acee8]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  16:     0x779948abe907 - rustc_middle[8f0bb18145f914db]::util::bug::span_bug_fmt::<rustc_span[75e5c439b5acee8]::span_encoding::Span>
  17:     0x77994c108492 - <rustc_middle[8f0bb18145f914db]::ty::instance::Instance>::expect_resolve
  18:     0x77994c414155 - <rustc_middle[8f0bb18145f914db]::ty::instance::Instance>::expect_resolve_for_vtable
  19:     0x77994c4cbfba - rustc_trait_selection[4ce5037939a8bd42]::traits::vtable::vtable_entries::{closure#0}
  20:     0x77994c4b9db4 - rustc_trait_selection[4ce5037939a8bd42]::traits::vtable::vtable_entries
  21:     0x77994c4b9aa0 - rustc_query_impl[1dc7e25d3505b9db]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[1dc7e25d3505b9db]::query_impl::vtable_entries::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8f0bb18145f914db]::query::erase::Erased<[u8; 16usize]>>
  22:     0x77994c4b9a5f - <rustc_query_impl[1dc7e25d3505b9db]::query_impl::vtable_entries::dynamic_query::{closure#2} as core[22e5dcc507c1ce60]::ops::function::FnOnce<(rustc_middle[8f0bb18145f914db]::ty::context::TyCtxt, rustc_type_ir[c825c5250d010cf3]::predicate::TraitRef<rustc_middle[8f0bb18145f914db]::ty::context::TyCtxt>)>>::call_once
  23:     0x77994c4b892e - rustc_query_system[923c01520de53f9e]::query::plumbing::try_execute_query::<rustc_query_impl[1dc7e25d3505b9db]::DynamicConfig<rustc_query_system[923c01520de53f9e]::query::caches::DefaultCache<rustc_type_ir[c825c5250d010cf3]::predicate::TraitRef<rustc_middle[8f0bb18145f914db]::ty::context::TyCtxt>, rustc_middle[8f0bb18145f914db]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[1dc7e25d3505b9db]::plumbing::QueryCtxt, false>
  24:     0x77994c4b862f - rustc_query_impl[1dc7e25d3505b9db]::query_impl::vtable_entries::get_query_non_incr::__rust_end_short_backtrace
  25:     0x77994aa2dafa - <rustc_const_eval[24ba1ca4ddcda3d4]::interpret::eval_context::InterpCx<rustc_const_eval[24ba1ca4ddcda3d4]::const_eval::dummy_machine::DummyMachine>>::vtable_entries
  26:     0x77994d3f9917 - <rustc_const_eval[24ba1ca4ddcda3d4]::interpret::eval_context::InterpCx<rustc_const_eval[24ba1ca4ddcda3d4]::const_eval::dummy_machine::DummyMachine>>::unsize_into_ptr.cold
  27:     0x77994c53e614 - <rustc_mir_transform[f79e9594970959e5]::gvn::VnState>::insert
  28:     0x77994c53a4ba - <rustc_mir_transform[f79e9594970959e5]::gvn::VnState>::simplify_rvalue::{closure#0}
  29:     0x7799491e97e6 - <rustc_mir_transform[f79e9594970959e5]::gvn::GVN as rustc_mir_transform[f79e9594970959e5]::pass_manager::MirPass>::run_pass
  30:     0x77994ba05533 - rustc_mir_transform[f79e9594970959e5]::pass_manager::run_passes_inner
  31:     0x77994c1a197b - rustc_mir_transform[f79e9594970959e5]::optimized_mir
  32:     0x77994c1a11a1 - rustc_query_impl[1dc7e25d3505b9db]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[1dc7e25d3505b9db]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8f0bb18145f914db]::query::erase::Erased<[u8; 8usize]>>
  33:     0x77994bc2040a - rustc_query_system[923c01520de53f9e]::query::plumbing::try_execute_query::<rustc_query_impl[1dc7e25d3505b9db]::DynamicConfig<rustc_query_system[923c01520de53f9e]::query::caches::DefIdCache<rustc_middle[8f0bb18145f914db]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[1dc7e25d3505b9db]::plumbing::QueryCtxt, false>
  34:     0x77994bc1f833 - rustc_query_impl[1dc7e25d3505b9db]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  35:     0x77994bf58e4a - <rustc_middle[8f0bb18145f914db]::ty::context::TyCtxt>::instance_mir
  36:     0x77994bd60867 - rustc_interface[d53afbea1eb411d7]::passes::run_required_analyses
  37:     0x77994ca2d95e - rustc_interface[d53afbea1eb411d7]::passes::analysis
  38:     0x77994ca2d92f - rustc_query_impl[1dc7e25d3505b9db]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[1dc7e25d3505b9db]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8f0bb18145f914db]::query::erase::Erased<[u8; 0usize]>>
  39:     0x77994ca17495 - rustc_query_system[923c01520de53f9e]::query::plumbing::try_execute_query::<rustc_query_impl[1dc7e25d3505b9db]::DynamicConfig<rustc_query_system[923c01520de53f9e]::query::caches::SingleCache<rustc_middle[8f0bb18145f914db]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[1dc7e25d3505b9db]::plumbing::QueryCtxt, false>
  40:     0x77994ca171ce - rustc_query_impl[1dc7e25d3505b9db]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  41:     0x77994cadaf3c - rustc_interface[d53afbea1eb411d7]::passes::create_and_enter_global_ctxt::<core[22e5dcc507c1ce60]::option::Option<rustc_interface[d53afbea1eb411d7]::queries::Linker>, rustc_driver_impl[345723d7f8fea549]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  42:     0x77994ca557e2 - rustc_interface[d53afbea1eb411d7]::interface::run_compiler::<(), rustc_driver_impl[345723d7f8fea549]::run_compiler::{closure#0}>::{closure#1}
  43:     0x77994c9d5898 - std[3b75b760e1909bee]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[d53afbea1eb411d7]::util::run_in_thread_with_globals<rustc_interface[d53afbea1eb411d7]::util::run_in_thread_pool_with_globals<rustc_interface[d53afbea1eb411d7]::interface::run_compiler<(), rustc_driver_impl[345723d7f8fea549]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  44:     0x77994c9d5574 - <<std[3b75b760e1909bee]::thread::Builder>::spawn_unchecked_<rustc_interface[d53afbea1eb411d7]::util::run_in_thread_with_globals<rustc_interface[d53afbea1eb411d7]::util::run_in_thread_pool_with_globals<rustc_interface[d53afbea1eb411d7]::interface::run_compiler<(), rustc_driver_impl[345723d7f8fea549]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[22e5dcc507c1ce60]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  45:     0x77994c9d4d2b - std::sys::pal::unix::thread::Thread::new::thread_start::h9b930113dc9df217
  46:     0x779946aa339d - <unknown>
  47:     0x779946b2849c - <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 1.87.0-nightly (ce36a966c 2025-02-17) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=5 -Z validate-mir -Z dump-mir-dir=dir

query stack during panic:
#0 [vtable_entries] finding all vtable entries for trait `Trait`
#1 [optimized_mir] optimizing MIR for `main`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0277`.

@rustbot label +F-trait_upcasting +-Zvalidate-mir

[matthiaskrgr]

bisects to #135318

[matthiaskrgr]

yeet!

trait A {
    fn b(&self);
}
trait C: A {}
impl C for () {}
fn d<e>(f: &dyn C) -> &dyn A {
    f
}
fn g() {
    d::<()>(&()).b()
}

[matthiaskrgr]

ah, this might be the none-errorguaranteed counterpart to #136381

[cyrgani]

a bit simpler:

trait A {
    fn b(&self);
}
trait C: A {}
impl C for () {}
fn main() {
    (&() as &dyn C as &dyn A).b();
}

then it just needs rustc -Zmir-opt-level=2 -Zvalidate-mir main.rs.

[compiler-errors]

This ICEs without any flags:

trait Supertrait<T> {
    fn method(&self) {}
}

trait Trait<P>: Supertrait<()> {}

impl<P> Trait<P> for () {}

const fn upcast<P>(x: &dyn Trait<P>) -> &dyn Supertrait<()> {
    x
}

const fn foo() -> &'static dyn Supertrait<()> {
    upcast::<()>(&())
}

const _: &'static dyn Supertrait<()> = foo();

[WaffleLapkin]

The generics and foo/upcast functions are not actually needed. All you need to trigger this ICE is an upcast in const to a supertrait which is not implemented:

trait Supertrait {
    fn method(&self) {}
}

trait Trait: Supertrait {}

impl Trait for () {}

const _: &dyn Supertrait = &() as &dyn Trait as &dyn Supertrait;