Rustc stable panics when optimizing MIR, attempting to unwrap trait object

[JoelCourtney]

Code

pub trait TestTrait {
    type MyType;
    fn func() -> Option<Self> where Self: Sized;
}

impl<T> dyn TestTrait<MyType = T> where Self: Sized {
    fn other_func() -> Option<Self> {
        match Self::func() {
            Some(me) => Some(me),
            None => None
        }
    }
}

This only happens when compiled in a library, not an executable.

The associated type MyType, both of the where Self: Sized's, the Option<Self> (instead of just Self), and the match statement are all needed to make it panic.

Replacing the match statement with Some(Self::func().unwrap()) errors gracefully, and says that I cannot call unwrap on a trait object; so I assume the error that should have been emitted for the match statement is that I cannot destructure a trait object.

Replacing the match with Self::func() compiles successfully.

Meta

This happens on stable, nightly, and beta.

rustc --version --verbose:

rustc 1.52.1 (9bc8c42bb 2021-05-09)
binary: rustc
commit-hash: 9bc8c42bb2f19e745a63f3445f1ac248fb015e53
commit-date: 2021-05-09
host: x86_64-apple-darwin
release: 1.52.1
LLVM version: 12.0.0

Error output

error: internal compiler error: compiler/rustc_mir/src/interpret/place.rs:44:17: expected wide pointer extra data (e.g. slice length or trait object vtable)

thread 'rustc' panicked at 'Box<Any>', /rustc/9bc8c42bb2f19e745a63f3445f1ac248fb015e53/library/std/src/panic.rs:59:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: 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: rustc 1.52.1 (9bc8c42bb 2021-05-09) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [optimized_mir] optimizing MIR for `<impl at src/lib.rs:6:1: 13:2>::other_func`
end of query stack

Backtrace

stack backtrace:
   0: std::panicking::begin_panic
   1: std::panic::panic_any
   2: rustc_errors::HandlerInner::bug
   3: rustc_errors::Handler::bug
   4: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
   5: rustc_middle::ty::context::tls::with_opt::{{closure}}
   6: rustc_middle::ty::context::tls::with_opt
   7: rustc_middle::util::bug::opt_span_bug_fmt
   8: rustc_middle::util::bug::bug_fmt
   9: rustc_mir::interpret::eval_context::InterpCx<M>::size_and_align_of
  10: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::place_field
  11: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_place
  12: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_rvalue_into_place
  13: <rustc_mir::transform::const_prop::ConstPropagator as rustc_middle::mir::visit::MutVisitor>::visit_statement
  14: <rustc_mir::transform::const_prop::ConstPropagator as rustc_middle::mir::visit::MutVisitor>::visit_body
  15: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  16: rustc_mir::transform::run_passes
  17: rustc_mir::transform::optimized_mir
  18: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  19: rustc_data_structures::stack::ensure_sufficient_stack
  20: rustc_query_system::query::plumbing::force_query_with_job
  21: rustc_query_system::query::plumbing::get_query_impl
  22: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::optimized_mir
  23: rustc_metadata::rmeta::encoder::EncodeContext::encode_crate_root
  24: rustc_metadata::rmeta::encoder::encode_metadata_impl
  25: rustc_data_structures::sync::join
  26: rustc_metadata::rmeta::decoder::cstore_impl::<impl rustc_middle::middle::cstore::CrateStore for rustc_metadata::creader::CStore>::encode_metadata
  27: rustc_middle::ty::context::TyCtxt::encode_metadata
  28: rustc_interface::passes::QueryContext::enter
  29: rustc_interface::queries::Queries::ongoing_codegen
  30: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  31: rustc_span::with_source_map
  32: rustc_interface::interface::create_compiler_and_run
  33: scoped_tls::ScopedKey<T>::set

[jonas-schievink]

also happens on nightly

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-medium

[JoelCourtney]

This ICE still exists, but the "internal compiler error" and "query stack during panic" sections of the error output have changed on 1.58.0-nightly.

Meta

rustc --version --verbose

rustc 1.58.0-nightly (8b09ba6a5 2021-11-09)
binary: rustc
commit-hash: 8b09ba6a5d5c644fe0f1c27c7f9c80b334241707
commit-date: 2021-11-09
host: x86_64-unknown-linux-gnu
release: 1.58.0-nightly
LLVM version: 13.0.0

I'm running this on a different machine than the one I initially posted the issue from.

Error Output

error: internal compiler error: /rustc/8b09ba6a5d5c644fe0f1c27c7f9c80b334241707/compiler/rustc_trait_selection/src/traits/util.rs:314:13: get_vtable_index_of_object_method: DefId(0:5 ~ scratch[c192]::TestTrait::func) was not found

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1169:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: 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: rustc 1.58.0-nightly (8b09ba6a5 2021-11-09) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [resolve_instance] resolving instance `<dyn TestTrait<MyType = T> as TestTrait>::func`
#1 [mir_built] building MIR for `<impl at src/lib.rs:6:1: 13:2>::other_func`
end of query stack

The output in 1.56.1-stable is still the same as it was when I originally posted the issue.

Backtrace

stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
   2: <rustc_errors::HandlerInner>::bug
   3: <rustc_errors::Handler>::bug
   4: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, ()>
   5: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>
   6: rustc_middle::util::bug::bug_fmt
   7: rustc_trait_selection::traits::util::get_vtable_index_of_object_method::<()>
   8: rustc_ty_utils::instance::inner_resolve_instance
   9: rustc_ty_utils::instance::resolve_instance
  10: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::ParamEnvAnd<(rustc_span::def_id::DefId, &rustc_middle::ty::list::List<rustc_middle::ty::subst::GenericArg>)>, core::result::Result<core::option::Option<rustc_middle::ty::instance::Instance>, rustc_errors::ErrorReported>>
  11: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::resolve_instance, rustc_query_impl::plumbing::QueryCtxt>
  12: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::resolve_instance
  13: <rustc_middle::ty::instance::Instance>::resolve
  14: <rustc_mir_build::lints::Search>::is_recursive_call
  15: <rustc_data_structures::graph::iterate::TriColorDepthFirstSearch<&rustc_middle::mir::Body>>::run_from_start::<rustc_mir_build::lints::Search>
  16: rustc_mir_build::lints::check
  17: <rustc_infer::infer::InferCtxtBuilder>::enter::<rustc_middle::mir::Body, rustc_mir_build::build::mir_build::{closure#1}>
  18: rustc_mir_build::build::mir_built
  19: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>
  20: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>::{closure#3}>
  21: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>>
  22: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_built
  23: rustc_mir_transform::check_unsafety::unsafety_check_result
  24: <rustc_mir_transform::check_unsafety::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
  25: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>
  26: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::mir::query::UnsafetyCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>::{closure#3}>
  27: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::UnsafetyCheckResult>>
  28: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  29: rustc_mir_transform::mir_const
  30: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>
  31: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>::{closure#3}>
  32: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, &rustc_data_structures::steal::Steal<rustc_middle::mir::Body>>>
  33: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const
  34: rustc_mir_transform::mir_promoted
  35: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, (&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>)>
  36: rustc_data_structures::stack::ensure_sufficient_stack::<((&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>), rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, (&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>)>::{closure#3}>
  37: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::WithOptConstParam<rustc_span::def_id::LocalDefId>, (&rustc_data_structures::steal::Steal<rustc_middle::mir::Body>, &rustc_data_structures::steal::Steal<rustc_index::vec::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body>>)>>
  38: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_promoted
  39: rustc_borrowck::mir_borrowck
  40: <rustc_borrowck::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
  41: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>
  42: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::mir::query::BorrowCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>::{closure#3}>
  43: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>>
  44: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
  45: <rustc_middle::hir::map::Map>::par_body_owners::<rustc_interface::passes::analysis::{closure#2}::{closure#0}>
  46: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#2}>
  47: rustc_interface::passes::analysis
  48: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>
  49: rustc_data_structures::stack::ensure_sufficient_stack::<(core::result::Result<(), rustc_errors::ErrorReported>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>::{closure#3}>
  50: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), core::result::Result<(), rustc_errors::ErrorReported>>>
  51: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
  52: <rustc_interface::passes::QueryContext>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}::{closure#3}, core::result::Result<(), rustc_errors::ErrorReported>>
  53: <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::ErrorReported>>
  54: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#0}>
  55: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>

query stack during panic:
#0 [resolve_instance] resolving instance `<dyn TestTrait<MyType = T> as TestTrait>::func`
#1 [mir_built] building MIR for `<impl at src/lib.rs:6:1: 13:2>::other_func`
#2 [unsafety_check_result] unsafety-checking `<impl at src/lib.rs:6:1: 13:2>::other_func`
#3 [mir_const] processing MIR for `<impl at src/lib.rs:6:1: 13:2>::other_func`
#4 [mir_promoted] processing `<impl at src/lib.rs:6:1: 13:2>::other_func`
#5 [mir_borrowck] borrow-checking `<impl at src/lib.rs:6:1: 13:2>::other_func`
#6 [analysis] running analysis passes on this crate
end of query stack

[JoelCourtney]

Additionally, the new ICE now happens when the code is compiled into an executable, but only on nightly. This didn't happen before. On 1.56.1-stable in src/main.rs, the compiler emits a warning that other_func is never used, and compiles successfully.

Edit: the error now happens on 1.60.0 stable when compiling in a binary as well.

[JohnTitor]

Triage: the issue has been fixed on the latest nightly, marking as E-needs-test.