nightly rustc panicked when no dyn before trait in type T =

[wychlw]

Code

trait T1{
    type T;
}
trait T2{
}
struct S {}
impl T1 for S{
    type T = T2;
}

fn main() {}

Compile with:

RUST_BACKTRACE=1 rustc --edition 2024 src/main.rs

Meta

rustc --version --verbose:

rustc 1.87.0-nightly (9fb94b32d 2025-03-10)
binary: rustc
commit-hash: 9fb94b32df38073bf63d009df77ed10cb1c989d0
commit-date: 2025-03-10
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Note: This panic won't happen if using a stable version rust.

Error output

thread 'rustc' panicked at compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs:210:61:
$ident: found ImplItem(ImplItem { ident: T#0, owner_id: DefId(0:9 ~ nfuzz[80de]::{impl#0}::T), generics: Generics { params: [], predicates: [], has_where_clause_predicates: false, where_clause_span: src/main.rs:9:16: 9:16 (#0), span: src/main.rs:9:11: 9:11 (#0) }, kind: Type(Ty { hir_id: HirId(DefId(0:9 ~ nfuzz[80de]::{impl#0}::T).4), span: src/main.rs:9:14: 9:16 (#0), kind: TraitObject([PolyTraitRef { bound_generic_params: [], modifiers: TraitBoundModifiers { constness: Never, polarity: Positive }, trait_ref: TraitRef { path: Path { span: src/main.rs:9:14: 9:16 (#0), res: Def(Trait, DefId(0:5 ~ nfuzz[80de]::T2)), segments: [PathSegment { ident: T2#0, hir_id: HirId(DefId(0:9 ~ nfuzz[80de]::{impl#0}::T).1), res: Def(Trait, DefId(0:5 ~ nfuzz[80de]::T2)), args: None, infer_args: false }] }, hir_ref_id: HirId(DefId(0:9 ~ nfuzz[80de]::{impl#0}::T).2) }, span: src/main.rs:9:14: 9:16 (#0) }], TaggedRef { pointer: Lifetime { hir_id: HirId(DefId(0:9 ~ nfuzz[80de]::{impl#0}::T).3), ident: #0, res: ImplicitObjectLifetimeDefault }, tag: None }) }), defaultness: Final, span: src/main.rs:9:5: 9:17 (#0), vis_span: src/main.rs:9:5: 9:5 (#0) })

Backtrace

thread 'rustc' panicked at compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs:210:61:
$ident: found ImplItem(ImplItem { ident: T#0, owner_id: DefId(0:9 ~ main[5c0d]::{impl#0}::T), generics: Generics { params: [], predicates: [], has_where_clause_predicates: false, where_clause_span: src/main.rs:9:16: 9:16 (#0), span: src/main.rs:9:11: 9:11 (#0) }, kind: Type(Ty { hir_id: HirId(DefId(0:9 ~ main[5c0d]::{impl#0}::T).4), span: src/main.rs:9:14: 9:16 (#0), kind: TraitObject([PolyTraitRef { bound_generic_params: [], modifiers: TraitBoundModifiers { constness: Never, polarity: Positive }, trait_ref: TraitRef { path: Path { span: src/main.rs:9:14: 9:16 (#0), res: Def(Trait, DefId(0:5 ~ main[5c0d]::T2)), segments: [PathSegment { ident: T2#0, hir_id: HirId(DefId(0:9 ~ main[5c0d]::{impl#0}::T).1), res: Def(Trait, DefId(0:5 ~ main[5c0d]::T2)), args: None, infer_args: false }] }, hir_ref_id: HirId(DefId(0:9 ~ main[5c0d]::{impl#0}::T).2) }, span: src/main.rs:9:14: 9:16 (#0) }], TaggedRef { pointer: Lifetime { hir_id: HirId(DefId(0:9 ~ main[5c0d]::{impl#0}::T).3), ident: #0, res: ImplicitObjectLifetimeDefault }, tag: None }) }), defaultness: Final, span: src/main.rs:9:5: 9:17 (#0), vis_span: src/main.rs:9:5: 9:5 (#0) })
stack backtrace:
   0:     0x7f83744bd7a5 - std::backtrace::Backtrace::create::h1c390fc3b8673de8
   1:     0x7f83727fe185 - std::backtrace::Backtrace::force_capture::h9092203d313dcaea
   2:     0x7f8371883dda - std[8d48930af2b37499]::panicking::update_hook::<alloc[917be3ddc91b1c2b]::boxed::Box<rustc_driver_impl[cb2ef720636d8c5e]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7f83728169a3 - std::panicking::rust_panic_with_hook::hdd2c1ee436bc47e1
   4:     0x7f837281669a - std::panicking::begin_panic_handler::{{closure}}::h2d122914997e8086
   5:     0x7f8372813e89 - std::sys::backtrace::__rust_end_short_backtrace::hd9079b2f352c9f4f
   6:     0x7f837281635d - rust_begin_unwind
   7:     0x7f836f26c570 - core::panicking::panic_fmt::h69773a3e9707cb82
   8:     0x7f8371951c31 - rustc_hir[b2623b24b2b871ce]::hir::expect_failed::<&rustc_hir[b2623b24b2b871ce]::hir::Node>
   9:     0x7f83742d2189 - <dyn rustc_hir_analysis[44b7779f9b34443e]::hir_ty_lowering::HirTyLowerer>::prohibit_or_lint_bare_trait_object_ty
  10:     0x7f8373589962 - <dyn rustc_hir_analysis[44b7779f9b34443e]::hir_ty_lowering::HirTyLowerer>::lower_ty
  11:     0x7f8373578bb5 - rustc_hir_analysis[44b7779f9b34443e]::collect::type_of::type_of
  12:     0x7f8373027866 - rustc_query_impl[5838e3d4961b7ce3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5838e3d4961b7ce3]::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 8usize]>>
  13:     0x7f83730266b2 - rustc_query_system[35a24321d428aa9e]::query::plumbing::try_execute_query::<rustc_query_impl[5838e3d4961b7ce3]::DynamicConfig<rustc_query_system[35a24321d428aa9e]::query::caches::DefIdCache<rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[5838e3d4961b7ce3]::plumbing::QueryCtxt, false>
  14:     0x7f837302625f - rustc_query_impl[5838e3d4961b7ce3]::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
  15:     0x7f83735a5202 - rustc_hir_analysis[44b7779f9b34443e]::check::wfcheck::check_well_formed
  16:     0x7f83735a3011 - rustc_query_impl[5838e3d4961b7ce3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5838e3d4961b7ce3]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 1usize]>>
  17:     0x7f83735a2ac8 - rustc_query_system[35a24321d428aa9e]::query::plumbing::try_execute_query::<rustc_query_impl[5838e3d4961b7ce3]::DynamicConfig<rustc_data_structures[3750d9ccf695a742]::vec_cache::VecCache<rustc_span[6a00076ff7f7ecaa]::def_id::LocalDefId, rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[35a24321d428aa9e]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[5838e3d4961b7ce3]::plumbing::QueryCtxt, false>
  18:     0x7f83735a2583 - rustc_query_impl[5838e3d4961b7ce3]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  19:     0x7f837359faa4 - rustc_hir_analysis[44b7779f9b34443e]::check::wfcheck::check_mod_type_wf
  20:     0x7f837359f89d - rustc_query_impl[5838e3d4961b7ce3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5838e3d4961b7ce3]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 1usize]>>
  21:     0x7f8373fd35d4 - rustc_query_system[35a24321d428aa9e]::query::plumbing::try_execute_query::<rustc_query_impl[5838e3d4961b7ce3]::DynamicConfig<rustc_query_system[35a24321d428aa9e]::query::caches::DefaultCache<rustc_span[6a00076ff7f7ecaa]::def_id::LocalModDefId, rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[5838e3d4961b7ce3]::plumbing::QueryCtxt, false>
  22:     0x7f8373fd337e - rustc_query_impl[5838e3d4961b7ce3]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7f8373583497 - rustc_hir_analysis[44b7779f9b34443e]::check_crate
  24:     0x7f83734400dd - rustc_interface[90e31f5b4a029d3a]::passes::run_required_analyses
  25:     0x7f8373fe1fb8 - rustc_interface[90e31f5b4a029d3a]::passes::analysis
  26:     0x7f8373fe1f97 - rustc_query_impl[5838e3d4961b7ce3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5838e3d4961b7ce3]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 0usize]>>
  27:     0x7f837411ac01 - rustc_query_system[35a24321d428aa9e]::query::plumbing::try_execute_query::<rustc_query_impl[5838e3d4961b7ce3]::DynamicConfig<rustc_query_system[35a24321d428aa9e]::query::caches::SingleCache<rustc_middle[602e8fb74d6cfd7]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[5838e3d4961b7ce3]::plumbing::QueryCtxt, false>
  28:     0x7f837411a8f4 - rustc_query_impl[5838e3d4961b7ce3]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f837435affc - rustc_interface[90e31f5b4a029d3a]::passes::create_and_enter_global_ctxt::<core[c99fea247d116993]::option::Option<rustc_interface[90e31f5b4a029d3a]::queries::Linker>, rustc_driver_impl[cb2ef720636d8c5e]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  30:     0x7f8374163817 - rustc_interface[90e31f5b4a029d3a]::interface::run_compiler::<(), rustc_driver_impl[cb2ef720636d8c5e]::run_compiler::{closure#0}>::{closure#1}
  31:     0x7f8373fc0fd2 - std[8d48930af2b37499]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[90e31f5b4a029d3a]::util::run_in_thread_with_globals<rustc_interface[90e31f5b4a029d3a]::util::run_in_thread_pool_with_globals<rustc_interface[90e31f5b4a029d3a]::interface::run_compiler<(), rustc_driver_impl[cb2ef720636d8c5e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  32:     0x7f8373fc18b4 - <<std[8d48930af2b37499]::thread::Builder>::spawn_unchecked_<rustc_interface[90e31f5b4a029d3a]::util::run_in_thread_with_globals<rustc_interface[90e31f5b4a029d3a]::util::run_in_thread_pool_with_globals<rustc_interface[90e31f5b4a029d3a]::interface::run_compiler<(), rustc_driver_impl[cb2ef720636d8c5e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[c99fea247d116993]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7f8373fc2cab - std::sys::pal::unix::thread::Thread::new::thread_start::h7dc228a213406109
  34:     0x7f836de6470a - <unknown>
  35:     0x7f836dee8aac - <unknown>
  36:                0x0 - <unknown>


rustc version: 1.87.0-nightly (9fb94b32d 2025-03-10)
platform: x86_64-unknown-linux-gnu

query stack during panic:
#0 [type_of] computing type of `<impl at src/main.rs:8:1: 8:14>::T`
#1 [check_well_formed] checking that `<impl at src/main.rs:8:1: 8:14>` is well-formed
#2 [check_mod_type_wf] checking that types are well-formed in top-level module
#3 [analysis] running analysis passes on this crate
end of query stack

[compiler-errors]

Should be fixed by #138238, which should be in today's nightly but will definitely be in tomorrow's.

[wychlw]

Confirm has been fixed :)
Thanks a lot!