ICE when missing trait bound in peculiar case

[konnorandrews]

Code

struct Demo<X, Y: A = X, Z = <<Y as A>::U as B>::V>(X, Y, Z);

impl<V> Demo<V> {
    fn new() {}
}

pub trait A<Group = ()> {
    type U: B;
}

pub trait B {
    type V;
}

Meta

rustc --version --verbose:

rustc 1.85.0 (4d91de4e4 2025-02-17)
binary: rustc
commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688
commit-date: 2025-02-17
host: x86_64-unknown-linux-gnu
release: 1.85.0
LLVM version: 19.1.7

Also happens on beta and nightly. Running with -Znext-solver does not have the ICE (the error is kept as expected). May be related to #133868.

Error output

error[E0277]: the trait bound `V: A` is not satisfied
 --> src/lib.rs:3:9
  |
3 | impl<V> Demo<V> {
  |         ^^^^^^^ the trait `A` is not implemented for `V`
  |
help: consider restricting type parameter `V` with trait `A`
  |
3 | impl<V: A> Demo<V> {
  |       +++

error: internal compiler error: compiler/rustc_trait_selection/src/traits/normalize.rs:69:17: deeply_normalize should not be called with pending obligations: [
                                    Obligation(predicate=Binder { value: ProjectionPredicate(AliasTerm { args: [?0t], def_id: DefId(0:18 ~ playground[465c]::B::V), .. }, Term::Ty(?1t)), bound_vars: [] }, depth=1),
                                ]
 --> src/lib.rs:3:9
  |
3 | impl<V> Demo<V> {
  |         ^^^^^^^

Backtrace

thread 'rustc' panicked at compiler/rustc_trait_selection/src/traits/normalize.rs:69:17:
Box<dyn Any>
stack backtrace:
   0:     0x78ca309cb634 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hc366073dd4ba6a4f
   1:     0x78ca31205aa2 - core::fmt::write::hb9256d1d79ff6859
   2:     0x78ca3259ddd1 - std::io::Write::write_fmt::hd9a4a51e43d6ab68
   3:     0x78ca309cb492 - std::sys::backtrace::BacktraceLock::print::h81b51ca9905b58b8
   4:     0x78ca309cdd72 - std::panicking::default_hook::{{closure}}::h800cff087746fb32
   5:     0x78ca309cd964 - std::panicking::default_hook::h8e77302320466097
   6:     0x78ca2fb24177 - std[7d1496126c658a52]::panicking::update_hook::<alloc[b94a15b63fd00bf8]::boxed::Box<rustc_driver_impl[95ea3323f115095d]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x78ca309ce5e3 - std::panicking::rust_panic_with_hook::hf2880f219899d673
   8:     0x78ca2fb60541 - std[7d1496126c658a52]::panicking::begin_panic::<rustc_errors[25a204b9d9cca0a9]::ExplicitBug>::{closure#0}
   9:     0x78ca2fb54a76 - std[7d1496126c658a52]::sys::backtrace::__rust_end_short_backtrace::<std[7d1496126c658a52]::panicking::begin_panic<rustc_errors[25a204b9d9cca0a9]::ExplicitBug>::{closure#0}, !>
  10:     0x78ca2fb54857 - std[7d1496126c658a52]::panicking::begin_panic::<rustc_errors[25a204b9d9cca0a9]::ExplicitBug>
  11:     0x78ca2fb69f41 - <rustc_errors[25a204b9d9cca0a9]::diagnostic::BugAbort as rustc_errors[25a204b9d9cca0a9]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x78ca300b9c0c - <rustc_errors[25a204b9d9cca0a9]::DiagCtxtHandle>::span_bug::<rustc_span[515292683a253d38]::span_encoding::Span, alloc[b94a15b63fd00bf8]::string::String>
  13:     0x78ca3014088a - rustc_middle[56e4ff076cda644b]::util::bug::opt_span_bug_fmt::<rustc_span[515292683a253d38]::span_encoding::Span>::{closure#0}
  14:     0x78ca3012838a - rustc_middle[56e4ff076cda644b]::ty::context::tls::with_opt::<rustc_middle[56e4ff076cda644b]::util::bug::opt_span_bug_fmt<rustc_span[515292683a253d38]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  15:     0x78ca301281fb - rustc_middle[56e4ff076cda644b]::ty::context::tls::with_context_opt::<rustc_middle[56e4ff076cda644b]::ty::context::tls::with_opt<rustc_middle[56e4ff076cda644b]::util::bug::opt_span_bug_fmt<rustc_span[515292683a253d38]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  16:     0x78ca2ea09267 - rustc_middle[56e4ff076cda644b]::util::bug::span_bug_fmt::<rustc_span[515292683a253d38]::span_encoding::Span>
  17:     0x78ca31609a4a - <rustc_trait_selection[635ca99423ce600e]::traits::engine::ObligationCtxt<rustc_trait_selection[635ca99423ce600e]::traits::FulfillmentError>>::assumed_wf_types_and_report_errors
  18:     0x78ca31a99d87 - rustc_hir_analysis[44a464fc9530b13d]::check::wfcheck::check_associated_item
  19:     0x78ca31974d57 - rustc_hir_analysis[44a464fc9530b13d]::check::wfcheck::check_well_formed
  20:     0x78ca3197338d - rustc_query_impl[ffcc3d1c9e8154f]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ffcc3d1c9e8154f]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[56e4ff076cda644b]::query::erase::Erased<[u8; 1usize]>>
  21:     0x78ca31972e44 - rustc_query_system[973ddc25b5c3187c]::query::plumbing::try_execute_query::<rustc_query_impl[ffcc3d1c9e8154f]::DynamicConfig<rustc_data_structures[16871ea2f26fa4bd]::vec_cache::VecCache<rustc_span[515292683a253d38]::def_id::LocalDefId, rustc_middle[56e4ff076cda644b]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[973ddc25b5c3187c]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[ffcc3d1c9e8154f]::plumbing::QueryCtxt, false>
  22:     0x78ca319728ff - rustc_query_impl[ffcc3d1c9e8154f]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  23:     0x78ca31970218 - rustc_hir_analysis[44a464fc9530b13d]::check::wfcheck::check_mod_type_wf
  24:     0x78ca3196ff1f - rustc_query_impl[ffcc3d1c9e8154f]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ffcc3d1c9e8154f]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[56e4ff076cda644b]::query::erase::Erased<[u8; 1usize]>>
  25:     0x78ca3229e856 - rustc_query_system[973ddc25b5c3187c]::query::plumbing::try_execute_query::<rustc_query_impl[ffcc3d1c9e8154f]::DynamicConfig<rustc_query_system[973ddc25b5c3187c]::query::caches::DefaultCache<rustc_span[515292683a253d38]::def_id::LocalModDefId, rustc_middle[56e4ff076cda644b]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[ffcc3d1c9e8154f]::plumbing::QueryCtxt, false>
  26:     0x78ca3229e5ff - rustc_query_impl[ffcc3d1c9e8154f]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  27:     0x78ca3155c18f - rustc_hir_analysis[44a464fc9530b13d]::check_crate
  28:     0x78ca316754b2 - rustc_interface[307c5e6bd736cecc]::passes::run_required_analyses
  29:     0x78ca3218637a - rustc_interface[307c5e6bd736cecc]::passes::analysis
  30:     0x78ca32186359 - rustc_query_impl[ffcc3d1c9e8154f]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ffcc3d1c9e8154f]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[56e4ff076cda644b]::query::erase::Erased<[u8; 0usize]>>
  31:     0x78ca322bef0b - rustc_query_system[973ddc25b5c3187c]::query::plumbing::try_execute_query::<rustc_query_impl[ffcc3d1c9e8154f]::DynamicConfig<rustc_query_system[973ddc25b5c3187c]::query::caches::SingleCache<rustc_middle[56e4ff076cda644b]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[ffcc3d1c9e8154f]::plumbing::QueryCtxt, false>
  32:     0x78ca322bebf9 - rustc_query_impl[ffcc3d1c9e8154f]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  33:     0x78ca3231623d - rustc_interface[307c5e6bd736cecc]::passes::create_and_enter_global_ctxt::<core[2ed51ce221d9613e]::option::Option<rustc_interface[307c5e6bd736cecc]::queries::Linker>, rustc_driver_impl[95ea3323f115095d]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  34:     0x78ca32306160 - rustc_interface[307c5e6bd736cecc]::interface::run_compiler::<(), rustc_driver_impl[95ea3323f115095d]::run_compiler::{closure#0}>::{closure#1}
  35:     0x78ca32194588 - std[7d1496126c658a52]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[307c5e6bd736cecc]::util::run_in_thread_with_globals<rustc_interface[307c5e6bd736cecc]::util::run_in_thread_pool_with_globals<rustc_interface[307c5e6bd736cecc]::interface::run_compiler<(), rustc_driver_impl[95ea3323f115095d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  36:     0x78ca32194e74 - <<std[7d1496126c658a52]::thread::Builder>::spawn_unchecked_<rustc_interface[307c5e6bd736cecc]::util::run_in_thread_with_globals<rustc_interface[307c5e6bd736cecc]::util::run_in_thread_pool_with_globals<rustc_interface[307c5e6bd736cecc]::interface::run_compiler<(), rustc_driver_impl[95ea3323f115095d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[2ed51ce221d9613e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  37:     0x78ca32196277 - std::sys::pal::unix::thread::Thread::new::thread_start::h39d9c8bec2c62e1a
  38:     0x78ca33786a94 - <unknown>
  39:     0x78ca33813a34 - clone
  40:                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: please attach the file at `/playground/rustc-ice-2025-03-08T09_02_47-24.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

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

query stack during panic:
#0 [check_well_formed] checking that `<impl at src/lib.rs:3:1: 3:16>::new` is well-formed
#1 [check_mod_type_wf] checking that types are well-formed in top-level module
... and 1 other queries... use `env RUST_BACKTRACE=1` to see the full query stack
For more information about this error, try `rustc --explain E0277`.