ICE: path with `Res::Err` but no error emitted

[matthiaskrgr]

Code

trait Foo {
    type Bar<'a>
    where
        Self: Sized;
    fn test(&self);
}
impl Foo for () {
    type Bar<'a>
        = ()
    where
        for<T> T:;
    fn test(&self) {}
}

pub fn main() {}

Meta

rustc --version --verbose:

rustc 1.93.0-nightly (94b49fd99 2025-11-22)
binary: rustc
commit-hash: 94b49fd998d6723e0a9240a7cff5f9df37b84dd8
commit-date: 2025-11-22
host: x86_64-unknown-linux-gnu
release: 1.93.0-nightly
LLVM version: 21.1.5

Error output

<output>

Backtrace

warning: trait `Foo` is never used
 --> /tmp/crash.rs:1:7
  |
1 | trait Foo {
  |       ^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: path with `Res::Err` but no error emitted
  --> /tmp/crash.rs:11:16
   |
11 |         for<T> T:;
   |                ^
   |
note: delayed at compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs:2117:22
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
         2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
         3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, &str>
         4: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_resolved_ty_path
         5: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
         6: rustc_hir_analysis::collect::predicates_of::gather_explicit_predicates_of::{closure#0}
         7: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::explicit_predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
         8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
         9: rustc_query_impl::query_impl::explicit_predicates_of::get_query_non_incr::__rust_end_short_backtrace
        10: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 24]>>
        11: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 24]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        12: rustc_query_impl::query_impl::predicates_of::get_query_non_incr::__rust_end_short_backtrace
        13: rustc_hir_analysis::check::compare_impl_item::compare_impl_item
        14: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::compare_impl_item::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        15: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        16: rustc_query_impl::query_impl::compare_impl_item::get_query_non_incr::__rust_end_short_backtrace
        17: rustc_hir_analysis::check::check::check_item_type
        18: rustc_hir_analysis::check::wfcheck::check_well_formed
        19: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        20: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        21: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
        22: rustc_hir_analysis::check::wfcheck::check_type_wf
        23: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        24: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        25: rustc_query_impl::query_impl::check_type_wf::get_query_non_incr::__rust_end_short_backtrace
        26: rustc_hir_analysis::check_crate
        27: rustc_interface::passes::analysis
        28: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
        29: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
        30: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
        31: <rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
        32: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        33: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
        34: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
        35: std::sys::thread::unix::Thread::new::thread_start
        36: <unknown>
        37: <unknown>

  --> /tmp/crash.rs:11:16
   |
11 |         for<T> T:;
   |                ^

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: please attach the file at `/home/matthias/vcs/github/glacier2_fuzz/fixed/rustc-ice-2025-11-23T07_37_43-1981379.txt` to your bug report

query stack during panic:
end of query stack

[matthiaskrgr]

happening since #147713

[chenyukang]

@fmease
I think it is related this part?
the ty is lowered with a type error and span_delayed_bug is set, but seems we now can handle that incomplete type in WF check.

rust/compiler/rustc_hir_analysis/src/collect/predicates_of.rs

Lines 273 to 281 in c871d09

	// Keep the type around in a dummy predicate. That way, it's not a complete
	// noop (see #53696) and `Ty` is still checked for WF.
	let span = bound_pred.bounded_ty.span;
	let predicate = ty::Binder::bind_with_vars(
	ty::ClauseKind::WellFormed(ty.into()),
	bound_vars,
	);
	predicates.insert((predicate.upcast(tcx), span));

[reddevilmidzy]

@rustbot claim