Next solver: ICE: Didn't expect to assemble trait candidate from […] NestedNormalizationGoals

[Josh194]

Code

struct Struct {}

trait Trait {}
impl<'a> Trait for &'a Struct {}

fn main() {
    let value = Struct {};

    fn func(arg: &Struct) -> &Struct { arg }

    fn wrap<F: Fn(&Struct) -> Ret, Ret: Trait>(f: F) {}
    wrap(func);
}

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (777d37277 2025-05-17)
binary: rustc
commit-hash: 777d372772aa3b39ba7273fcb8208a89f2ab0afd
commit-date: 2025-05-17
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.4

Error output

error: internal compiler error: compiler/rustc_trait_selection/src/solve/select.rs:185:13: didn't expect to assemble trait candidate from Root {
                                    result: Ok(
                                        Canonical {
                                            value: Response {
                                                certainty: Yes,
                                                var_values: CanonicalVarValues {
                                                    var_values: [],
                                                },
                                                external_constraints: ExternalConstraints(
                                                    ExternalConstraintsData {
                                                        region_constraints: [],
                                                        opaque_types: [],
                                                        normalization_nested_goals: NestedNormalizationGoals(
                                                            [],
                                                        ),
                                                    },
                                                ),
                                            },
                                            max_universe: U0,
                                            variables: [],
                                        },
                                    ),
                                }
  --> <source>:12:10
   |
12 |     wrap(func);
   |          ^^^^

Backtrace

thread 'rustc' panicked at compiler/rustc_trait_selection/src/solve/select.rs:185:13:
Box<dyn Any>
stack backtrace:
   0:     0x78025376f063 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::ha391d80b5e68e919
   1:     0x780253e05977 - core::fmt::write::h1cecefcb305d1155
   2:     0x780254ed00d1 - std::io::Write::write_fmt::h41ef61269065dc96
   3:     0x78025376eec2 - std::sys::backtrace::BacktraceLock::print::h5ae784575c381c12
   4:     0x780253772aba - std::panicking::default_hook::{{closure}}::h72fa7b5ed73b3cb2
   5:     0x78025377263f - std::panicking::default_hook::he27598d97fb5e6bc
   6:     0x78025279dbb3 - std[13072b276e939a5d]::panicking::update_hook::<alloc[cdfabe42c5865433]::boxed::Box<rustc_driver_impl[b40d209f1534a115]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x780253773333 - std::panicking::rust_panic_with_hook::h0e25468a64f50749
   8:     0x7802527da011 - std[13072b276e939a5d]::panicking::begin_panic::<rustc_errors[e76d1cc800a3cd8b]::ExplicitBug>::{closure#0}
   9:     0x7802527cdee6 - std[13072b276e939a5d]::sys::backtrace::__rust_end_short_backtrace::<std[13072b276e939a5d]::panicking::begin_panic<rustc_errors[e76d1cc800a3cd8b]::ExplicitBug>::{closure#0}, !>
  10:     0x7802527ca5f9 - std[13072b276e939a5d]::panicking::begin_panic::<rustc_errors[e76d1cc800a3cd8b]::ExplicitBug>
  11:     0x7802527e4661 - <rustc_errors[e76d1cc800a3cd8b]::diagnostic::BugAbort as rustc_errors[e76d1cc800a3cd8b]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x780252db646c - <rustc_errors[e76d1cc800a3cd8b]::DiagCtxtHandle>::span_bug::<rustc_span[fc860b16118515f6]::span_encoding::Span, alloc[cdfabe42c5865433]::string::String>
  13:     0x780252e535b7 - rustc_middle[e21e39dd30abbfc2]::util::bug::opt_span_bug_fmt::<rustc_span[fc860b16118515f6]::span_encoding::Span>::{closure#0}
  14:     0x780252e2cdea - rustc_middle[e21e39dd30abbfc2]::ty::context::tls::with_opt::<rustc_middle[e21e39dd30abbfc2]::util::bug::opt_span_bug_fmt<rustc_span[fc860b16118515f6]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  15:     0x780252e2cc5b - rustc_middle[e21e39dd30abbfc2]::ty::context::tls::with_context_opt::<rustc_middle[e21e39dd30abbfc2]::ty::context::tls::with_opt<rustc_middle[e21e39dd30abbfc2]::util::bug::opt_span_bug_fmt<rustc_span[fc860b16118515f6]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  16:     0x7802518ff787 - rustc_middle[e21e39dd30abbfc2]::util::bug::span_bug_fmt::<rustc_span[fc860b16118515f6]::span_encoding::Span>
  17:     0x7802535f62d8 - rustc_trait_selection[f9a05ecbd46dce9e]::solve::select::to_selection
  18:     0x7802535f57d4 - <rustc_trait_selection[f9a05ecbd46dce9e]::solve::select::Select as rustc_trait_selection[f9a05ecbd46dce9e]::solve::inspect::analyse::ProofTreeVisitor>::visit_goal
  19:     0x78025362dc22 - <rustc_infer[203a4dcd60087c62]::infer::InferCtxt as rustc_trait_selection[f9a05ecbd46dce9e]::solve::select::InferCtxtSelectExt>::select_in_new_trait_solver
  20:     0x7802535e58ed - <rustc_trait_selection[f9a05ecbd46dce9e]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  21:     0x7802540ca9bc - <rustc_hir_typeck[f50ac000c2ae270]::fn_ctxt::FnCtxt>::check_expr_call
  22:     0x780254c95def - <rustc_hir_typeck[f50ac000c2ae270]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  23:     0x780250545d83 - <rustc_hir_typeck[f50ac000c2ae270]::fn_ctxt::FnCtxt>::check_expr_block
  24:     0x780254c968e7 - <rustc_hir_typeck[f50ac000c2ae270]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  25:     0x7802543f07e5 - rustc_hir_typeck[f50ac000c2ae270]::check::check_fn
  26:     0x7802543db351 - rustc_hir_typeck[f50ac000c2ae270]::typeck_with_inspect::{closure#0}
  27:     0x7802543da036 - rustc_query_impl[da4220149538f346]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[da4220149538f346]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e21e39dd30abbfc2]::query::erase::Erased<[u8; 8usize]>>
  28:     0x7802540ed426 - rustc_query_system[83aca0075238f65e]::query::plumbing::try_execute_query::<rustc_query_impl[da4220149538f346]::DynamicConfig<rustc_data_structures[548a2e6de72614fc]::vec_cache::VecCache<rustc_span[fc860b16118515f6]::def_id::LocalDefId, rustc_middle[e21e39dd30abbfc2]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[83aca0075238f65e]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[da4220149538f346]::plumbing::QueryCtxt, false>
  29:     0x7802540ece92 - rustc_query_impl[da4220149538f346]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7802540eb6c9 - rustc_hir_analysis[ab2364e84e94296d]::check_crate
  31:     0x7802542c1bc5 - rustc_interface[e200ad1770586edd]::passes::run_required_analyses
  32:     0x780254d7371e - rustc_interface[e200ad1770586edd]::passes::analysis
  33:     0x780254d736f5 - rustc_query_impl[da4220149538f346]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[da4220149538f346]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e21e39dd30abbfc2]::query::erase::Erased<[u8; 0usize]>>
  34:     0x780254d757fa - rustc_query_system[83aca0075238f65e]::query::plumbing::try_execute_query::<rustc_query_impl[da4220149538f346]::DynamicConfig<rustc_query_system[83aca0075238f65e]::query::caches::SingleCache<rustc_middle[e21e39dd30abbfc2]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[da4220149538f346]::plumbing::QueryCtxt, false>
  35:     0x780254d754cf - rustc_query_impl[da4220149538f346]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  36:     0x780255071587 - rustc_interface[e200ad1770586edd]::passes::create_and_enter_global_ctxt::<core[ce55df5acd2c727e]::option::Option<rustc_interface[e200ad1770586edd]::queries::Linker>, rustc_driver_impl[b40d209f1534a115]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  37:     0x780254f12ca6 - rustc_interface[e200ad1770586edd]::interface::run_compiler::<(), rustc_driver_impl[b40d209f1534a115]::run_compiler::{closure#0}>::{closure#1}
  38:     0x780254ec6d7e - std[13072b276e939a5d]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e200ad1770586edd]::util::run_in_thread_with_globals<rustc_interface[e200ad1770586edd]::util::run_in_thread_pool_with_globals<rustc_interface[e200ad1770586edd]::interface::run_compiler<(), rustc_driver_impl[b40d209f1534a115]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  39:     0x780254ec71eb - <<std[13072b276e939a5d]::thread::Builder>::spawn_unchecked_<rustc_interface[e200ad1770586edd]::util::run_in_thread_with_globals<rustc_interface[e200ad1770586edd]::util::run_in_thread_pool_with_globals<rustc_interface[e200ad1770586edd]::interface::run_compiler<(), rustc_driver_impl[b40d209f1534a115]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[ce55df5acd2c727e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  40:     0x780254ec85eb - std::sys::pal::unix::thread::Thread::new::thread_start::h705253a14e119c3f
  41:     0x78024ea94ac3 - <unknown>
  42:     0x78024eb26850 - <unknown>
  43:                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 `/app/rustc-ice-2025-05-21T06_59_45-1.txt` to your bug report

note: compiler flags: -C debuginfo=2 -C llvm-args=--x86-asm-syntax=intel --crate-type rlib -Z next-solver

query stack during panic:
#0 [typeck] type-checking `main`
#1 [analysis] running analysis passes on this crate
end of query stack

[theemathas]

Version without the Fn trait:

trait Trait<'a> {
    type Assoc;
}

struct Thing;

impl<'a> Trait<'a> for Thing {
    type Assoc = &'a i32;
}

fn wrap<T, U: for<'a> Trait<'a, Assoc = T>>() {}

fn foo() {
    wrap::<_, Thing>();
}