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ICE: `Failed to normalize Alias(Opaque`

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-Zvalidate-mir C-bug I-ICE T-compiler WG-trait-system-refactor
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Description

auto-reduced (treereduce-rust):

//@compile-flags: -Zvalidate-mir -Znext-solver=globally
//

trait Quux {}

fn foo() -> impl Quux {
    struct Foo<T>(T);
    impl<T> Quux for Foo<T> {}
    Foo(bar())
}

fn bar() -> impl Quux {
    struct Bar<T>(T);
    impl<T> Quux for Bar<T> {}
    Bar(foo())
}

original:

// Test that attempts to construct infinite types via impl trait fail
// in a graceful way.
//
// Regression test for #38064.

trait Quux {}

fn foo() -> impl Quux { //~ ERROR cannot resolve opaque type
    struct Foo<T>(T);
    impl<T> Quux for Foo<T> {}
    Foo(bar())
}

fn bar() -> impl Quux { //~ ERROR cannot resolve opaque type
    struct Bar<T>(T);
    impl<T> Quux for Bar<T> {}
    Bar(foo())
}

// effectively:
//     struct Foo(Bar);
//     struct Bar(Foo);
// should produce an error about infinite size

fn main() { foo(); }

Version information

rustc 1.95.0-nightly (621d76794 2026-01-18)
binary: rustc
commit-hash: 621d76794c76fc21c0a6151fbc090120e0230a91
commit-date: 2026-01-18
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Possibly related line of code:
https://github.com/rust-lang/rust/blob/621d76794c76fc21c0a6151fbc090120e0230a91/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs#L165-L177

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zvalidate-mir -Znext-solver=globally

Program output 

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.bEsLPnBIxAck/rustc_testrunner_tmpdir_reporting.QgLDyvukeBZz/mvce.rs:15:2
   |
15 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.bEsLPnBIxAck/rustc_testrunner_tmpdir_reporting.QgLDyvukeBZz/mvce.rs`

error[E0720]: cannot resolve opaque type
  --> /tmp/icemaker_global_tempdir.bEsLPnBIxAck/rustc_testrunner_tmpdir_reporting.QgLDyvukeBZz/mvce.rs:5:13
   |
 5 | fn foo() -> impl Quux {
   |             ^^^^^^^^^ recursive opaque type
...
 8 |     Foo(bar())
   |     ---------- returning here with type `Foo<impl Quux>`
...
11 | fn bar() -> impl Quux {
   |             --------- returning this type `Foo<impl Quux>`

error[E0720]: cannot resolve opaque type
  --> /tmp/icemaker_global_tempdir.bEsLPnBIxAck/rustc_testrunner_tmpdir_reporting.QgLDyvukeBZz/mvce.rs:11:13
   |
 5 | fn foo() -> impl Quux {
   |             --------- returning this type `Bar<impl Quux>`
...
11 | fn bar() -> impl Quux {
   |             ^^^^^^^^^ recursive opaque type
...
14 |     Bar(foo())
   |     ---------- returning here with type `Bar<impl Quux>`

error: internal compiler error: /rustc-dev/621d76794c76fc21c0a6151fbc090120e0230a91/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:171:13: Failed to normalize Alias(Opaque, AliasTy { args: [], def_id: DefId(0:13 ~ mvce[a621]::bar::{opaque#0}), .. }) in typing_env=TypingEnv { typing_mode: PostAnalysis, param_env: ParamEnv { caller_bounds: [] } }, maybe try to call `try_normalize_erasing_regions` instead


thread 'rustc' (859947) panicked at /rustc-dev/621d76794c76fc21c0a6151fbc090120e0230a91/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:171:13:
Box<dyn Any>
stack backtrace:
   0:     0x7f3a4c433fd3 - <<std[287527946f71f0bc]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[7477a31a1a34cc49]::fmt::Display>::fmt
   1:     0x7f3a4ca0e2c8 - core[7477a31a1a34cc49]::fmt::write
   2:     0x7f3a4c44a9c6 - <std[287527946f71f0bc]::sys::stdio::unix::Stderr as std[287527946f71f0bc]::io::Write>::write_fmt
   3:     0x7f3a4c40a048 - std[287527946f71f0bc]::panicking::default_hook::{closure#0}
   4:     0x7f3a4c427703 - std[287527946f71f0bc]::panicking::default_hook
   5:     0x7f3a4b3fbb8a - std[287527946f71f0bc]::panicking::update_hook::<alloc[979041e9952e771b]::boxed::Box<rustc_driver_impl[517260a07841a630]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f3a4c4279e2 - std[287527946f71f0bc]::panicking::panic_with_hook
   7:     0x7f3a4b438bc1 - std[287527946f71f0bc]::panicking::begin_panic::<rustc_errors[26c9ea40265c581b]::ExplicitBug>::{closure#0}
   8:     0x7f3a4b428fe6 - std[287527946f71f0bc]::sys::backtrace::__rust_end_short_backtrace::<std[287527946f71f0bc]::panicking::begin_panic<rustc_errors[26c9ea40265c581b]::ExplicitBug>::{closure#0}, !>
   9:     0x7f3a4b4264b9 - std[287527946f71f0bc]::panicking::begin_panic::<rustc_errors[26c9ea40265c581b]::ExplicitBug>
  10:     0x7f3a4b456901 - <rustc_errors[26c9ea40265c581b]::diagnostic::BugAbort as rustc_errors[26c9ea40265c581b]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7f3a4ba074f9 - rustc_middle[725063e074f29df]::util::bug::opt_span_bug_fmt::<rustc_span[851f35e07e3c2dd4]::span_encoding::Span>::{closure#0}
  12:     0x7f3a4ba07682 - rustc_middle[725063e074f29df]::ty::context::tls::with_opt::<rustc_middle[725063e074f29df]::util::bug::opt_span_bug_fmt<rustc_span[851f35e07e3c2dd4]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7f3a4b9f8cab - rustc_middle[725063e074f29df]::ty::context::tls::with_context_opt::<rustc_middle[725063e074f29df]::ty::context::tls::with_opt<rustc_middle[725063e074f29df]::util::bug::opt_span_bug_fmt<rustc_span[851f35e07e3c2dd4]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7f3a48e91cc4 - rustc_middle[725063e074f29df]::util::bug::bug_fmt
  15:     0x7f3a4cc5bf74 - <rustc_middle[725063e074f29df]::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc_type_ir[b93cf349b3a4f34d]::fold::TypeFolder<rustc_middle[725063e074f29df]::ty::context::TyCtxt>>::fold_ty
  16:     0x7f3a4d5bfa8d - rustc_mir_transform[f63ee9052e691c]::validate::validate_types
  17:     0x7f3a4d5b4946 - <rustc_mir_transform[f63ee9052e691c]::validate::Validator as rustc_mir_transform[f63ee9052e691c]::pass_manager::MirPass>::run_pass
  18:     0x7f3a4a15d7a5 - rustc_mir_transform[f63ee9052e691c]::pass_manager::validate_body
  19:     0x7f3a4ca0b494 - rustc_mir_transform[f63ee9052e691c]::run_analysis_to_runtime_passes
  20:     0x7f3a4d7a9e80 - rustc_mir_transform[f63ee9052e691c]::mir_drops_elaborated_and_const_checked
  21:     0x7f3a4d7a9829 - rustc_query_impl[f20b8284200e680a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f20b8284200e680a]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 8usize]>>
  22:     0x7f3a4cb5522a - rustc_query_system[b7e73caa2c2ad9a]::query::plumbing::try_execute_query::<rustc_query_impl[f20b8284200e680a]::DynamicConfig<rustc_data_structures[e0d8483206daafa2]::vec_cache::VecCache<rustc_span[851f35e07e3c2dd4]::def_id::LocalDefId, rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[b7e73caa2c2ad9a]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[f20b8284200e680a]::plumbing::QueryCtxt, false>
  23:     0x7f3a4cb548cd - rustc_query_impl[f20b8284200e680a]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  24:     0x7f3a4cb4c4ff - <rustc_middle[725063e074f29df]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[5c48368f5debe80d]::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
  25:     0x7f3a4cb49c0a - rustc_interface[5c48368f5debe80d]::passes::analysis
  26:     0x7f3a4cb49035 - rustc_query_impl[f20b8284200e680a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f20b8284200e680a]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 0usize]>>
  27:     0x7f3a4dba4be3 - rustc_query_system[b7e73caa2c2ad9a]::query::plumbing::try_execute_query::<rustc_query_impl[f20b8284200e680a]::DynamicConfig<rustc_query_system[b7e73caa2c2ad9a]::query::caches::SingleCache<rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[f20b8284200e680a]::plumbing::QueryCtxt, false>
  28:     0x7f3a4dba49ce - rustc_query_impl[f20b8284200e680a]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f3a4dd82c11 - <rustc_interface[5c48368f5debe80d]::passes::create_and_enter_global_ctxt<core[7477a31a1a34cc49]::option::Option<rustc_interface[5c48368f5debe80d]::queries::Linker>, rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[7477a31a1a34cc49]::ops::function::FnOnce<(&rustc_session[eb79e6d3104f29ae]::session::Session, rustc_middle[725063e074f29df]::ty::context::CurrentGcx, alloc[979041e9952e771b]::sync::Arc<rustc_data_structures[e0d8483206daafa2]::jobserver::Proxy>, &std[287527946f71f0bc]::sync::once_lock::OnceLock<rustc_middle[725063e074f29df]::ty::context::GlobalCtxt>, &rustc_data_structures[e0d8483206daafa2]::sync::worker_local::WorkerLocal<rustc_middle[725063e074f29df]::arena::Arena>, &rustc_data_structures[e0d8483206daafa2]::sync::worker_local::WorkerLocal<rustc_hir[7eac7792dedc1861]::Arena>, rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  30:     0x7f3a4dbf5d34 - rustc_interface[5c48368f5debe80d]::interface::run_compiler::<(), rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}>::{closure#1}
  31:     0x7f3a4db5aa3a - std[287527946f71f0bc]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5c48368f5debe80d]::util::run_in_thread_with_globals<rustc_interface[5c48368f5debe80d]::util::run_in_thread_pool_with_globals<rustc_interface[5c48368f5debe80d]::interface::run_compiler<(), rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  32:     0x7f3a4db5a7fe - <std[287527946f71f0bc]::thread::lifecycle::spawn_unchecked<rustc_interface[5c48368f5debe80d]::util::run_in_thread_with_globals<rustc_interface[5c48368f5debe80d]::util::run_in_thread_pool_with_globals<rustc_interface[5c48368f5debe80d]::interface::run_compiler<(), rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[7477a31a1a34cc49]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7f3a4db5c5c4 - <std[287527946f71f0bc]::sys::thread::unix::Thread>::new::thread_start
  34:     0x7f3a4749698b - <unknown>
  35:     0x7f3a4751a9cc - <unknown>
  36:                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 1.95.0-nightly (621d76794 2026-01-18) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z validate-mir -Z next-solver=globally -Z dump-mir-dir=dir

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `foo`
#1 [analysis] running analysis passes on crate `mvce`
end of query stack
error: internal compiler error: /rustc-dev/621d76794c76fc21c0a6151fbc090120e0230a91/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:171:13: Failed to normalize Alias(Opaque, AliasTy { args: [], def_id: DefId(0:5 ~ mvce[a621]::foo::{opaque#0}), .. }) in typing_env=TypingEnv { typing_mode: PostAnalysis, param_env: ParamEnv { caller_bounds: [] } }, maybe try to call `try_normalize_erasing_regions` instead


thread 'rustc' (859947) panicked at /rustc-dev/621d76794c76fc21c0a6151fbc090120e0230a91/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:171:13:
Box<dyn Any>
stack backtrace:
   0:     0x7f3a4c433fd3 - <<std[287527946f71f0bc]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[7477a31a1a34cc49]::fmt::Display>::fmt
   1:     0x7f3a4ca0e2c8 - core[7477a31a1a34cc49]::fmt::write
   2:     0x7f3a4c44a9c6 - <std[287527946f71f0bc]::sys::stdio::unix::Stderr as std[287527946f71f0bc]::io::Write>::write_fmt
   3:     0x7f3a4c40a048 - std[287527946f71f0bc]::panicking::default_hook::{closure#0}
   4:     0x7f3a4c427703 - std[287527946f71f0bc]::panicking::default_hook
   5:     0x7f3a4b3fbb8a - std[287527946f71f0bc]::panicking::update_hook::<alloc[979041e9952e771b]::boxed::Box<rustc_driver_impl[517260a07841a630]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f3a4c4279e2 - std[287527946f71f0bc]::panicking::panic_with_hook
   7:     0x7f3a4b438bc1 - std[287527946f71f0bc]::panicking::begin_panic::<rustc_errors[26c9ea40265c581b]::ExplicitBug>::{closure#0}
   8:     0x7f3a4b428fe6 - std[287527946f71f0bc]::sys::backtrace::__rust_end_short_backtrace::<std[287527946f71f0bc]::panicking::begin_panic<rustc_errors[26c9ea40265c581b]::ExplicitBug>::{closure#0}, !>
   9:     0x7f3a4b4264b9 - std[287527946f71f0bc]::panicking::begin_panic::<rustc_errors[26c9ea40265c581b]::ExplicitBug>
  10:     0x7f3a4b456901 - <rustc_errors[26c9ea40265c581b]::diagnostic::BugAbort as rustc_errors[26c9ea40265c581b]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7f3a4ba074f9 - rustc_middle[725063e074f29df]::util::bug::opt_span_bug_fmt::<rustc_span[851f35e07e3c2dd4]::span_encoding::Span>::{closure#0}
  12:     0x7f3a4ba07682 - rustc_middle[725063e074f29df]::ty::context::tls::with_opt::<rustc_middle[725063e074f29df]::util::bug::opt_span_bug_fmt<rustc_span[851f35e07e3c2dd4]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7f3a4b9f8cab - rustc_middle[725063e074f29df]::ty::context::tls::with_context_opt::<rustc_middle[725063e074f29df]::ty::context::tls::with_opt<rustc_middle[725063e074f29df]::util::bug::opt_span_bug_fmt<rustc_span[851f35e07e3c2dd4]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7f3a48e91cc4 - rustc_middle[725063e074f29df]::util::bug::bug_fmt
  15:     0x7f3a4cc5bf74 - <rustc_middle[725063e074f29df]::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc_type_ir[b93cf349b3a4f34d]::fold::TypeFolder<rustc_middle[725063e074f29df]::ty::context::TyCtxt>>::fold_ty
  16:     0x7f3a4d5bfa8d - rustc_mir_transform[f63ee9052e691c]::validate::validate_types
  17:     0x7f3a4d5b4946 - <rustc_mir_transform[f63ee9052e691c]::validate::Validator as rustc_mir_transform[f63ee9052e691c]::pass_manager::MirPass>::run_pass
  18:     0x7f3a4a15d7a5 - rustc_mir_transform[f63ee9052e691c]::pass_manager::validate_body
  19:     0x7f3a4ca0b494 - rustc_mir_transform[f63ee9052e691c]::run_analysis_to_runtime_passes
  20:     0x7f3a4d7a9e80 - rustc_mir_transform[f63ee9052e691c]::mir_drops_elaborated_and_const_checked
  21:     0x7f3a4d7a9829 - rustc_query_impl[f20b8284200e680a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f20b8284200e680a]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 8usize]>>
  22:     0x7f3a4cb5522a - rustc_query_system[b7e73caa2c2ad9a]::query::plumbing::try_execute_query::<rustc_query_impl[f20b8284200e680a]::DynamicConfig<rustc_data_structures[e0d8483206daafa2]::vec_cache::VecCache<rustc_span[851f35e07e3c2dd4]::def_id::LocalDefId, rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[b7e73caa2c2ad9a]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[f20b8284200e680a]::plumbing::QueryCtxt, false>
  23:     0x7f3a4cb548cd - rustc_query_impl[f20b8284200e680a]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  24:     0x7f3a4cb4c4ff - <rustc_middle[725063e074f29df]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[5c48368f5debe80d]::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
  25:     0x7f3a4cb49c0a - rustc_interface[5c48368f5debe80d]::passes::analysis
  26:     0x7f3a4cb49035 - rustc_query_impl[f20b8284200e680a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f20b8284200e680a]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 0usize]>>
  27:     0x7f3a4dba4be3 - rustc_query_system[b7e73caa2c2ad9a]::query::plumbing::try_execute_query::<rustc_query_impl[f20b8284200e680a]::DynamicConfig<rustc_query_system[b7e73caa2c2ad9a]::query::caches::SingleCache<rustc_middle[725063e074f29df]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[f20b8284200e680a]::plumbing::QueryCtxt, false>
  28:     0x7f3a4dba49ce - rustc_query_impl[f20b8284200e680a]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f3a4dd82c11 - <rustc_interface[5c48368f5debe80d]::passes::create_and_enter_global_ctxt<core[7477a31a1a34cc49]::option::Option<rustc_interface[5c48368f5debe80d]::queries::Linker>, rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[7477a31a1a34cc49]::ops::function::FnOnce<(&rustc_session[eb79e6d3104f29ae]::session::Session, rustc_middle[725063e074f29df]::ty::context::CurrentGcx, alloc[979041e9952e771b]::sync::Arc<rustc_data_structures[e0d8483206daafa2]::jobserver::Proxy>, &std[287527946f71f0bc]::sync::once_lock::OnceLock<rustc_middle[725063e074f29df]::ty::context::GlobalCtxt>, &rustc_data_structures[e0d8483206daafa2]::sync::worker_local::WorkerLocal<rustc_middle[725063e074f29df]::arena::Arena>, &rustc_data_structures[e0d8483206daafa2]::sync::worker_local::WorkerLocal<rustc_hir[7eac7792dedc1861]::Arena>, rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  30:     0x7f3a4dbf5d34 - rustc_interface[5c48368f5debe80d]::interface::run_compiler::<(), rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}>::{closure#1}
  31:     0x7f3a4db5aa3a - std[287527946f71f0bc]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5c48368f5debe80d]::util::run_in_thread_with_globals<rustc_interface[5c48368f5debe80d]::util::run_in_thread_pool_with_globals<rustc_interface[5c48368f5debe80d]::interface::run_compiler<(), rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  32:     0x7f3a4db5a7fe - <std[287527946f71f0bc]::thread::lifecycle::spawn_unchecked<rustc_interface[5c48368f5debe80d]::util::run_in_thread_with_globals<rustc_interface[5c48368f5debe80d]::util::run_in_thread_pool_with_globals<rustc_interface[5c48368f5debe80d]::interface::run_compiler<(), rustc_driver_impl[517260a07841a630]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[7477a31a1a34cc49]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7f3a4db5c5c4 - <std[287527946f71f0bc]::sys::thread::unix::Thread>::new::thread_start
  34:     0x7f3a4749698b - <unknown>
  35:     0x7f3a4751a9cc - <unknown>
  36:                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 1.95.0-nightly (621d76794 2026-01-18) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z validate-mir -Z next-solver=globally -Z dump-mir-dir=dir

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `bar`
#1 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 5 previous errors

Some errors have detailed explanations: E0601, E0720.
For more information about an error, try `rustc --explain E0601`.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the reduced reproducer and run it using -Zvalidate-mir -Znext-solver=globally. Read compiler/rustc_middle/src/ty/normalize_erasing_regions.rs around line 171 and the rustc_mir_transform validate_types entry point shown in the query stack. Done means the recursive opaque-type example reports the expected E0720 errors without an internal compiler error.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
42/100

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