ice: unexpected free variable with depth ^1.0 with outer binder ^0

[matthiaskrgr]

trait MapLookup<Q> {
    type MapValue;
}

impl<K> MapLookup<K> for K {
    type MapValue = K;
}

trait Map: MapLookup<<Self as Map>::Key> {
    type Key;
}

impl<K> Map for K {
    type Key = K;
}


fn main() {
    let _ = &()
        as &dyn Map<Key=u32,MapValue=u32>;
    //~^ ERROR E0038
}

rust-analyzer 1.77.0-nightly (595bc6f 2024-01-05)
rust-analyzer highlight < issue-26056.rs

thread 'main' panicked at /rust/deps/chalk-ir-0.95.0/src/fold.rs:437:13:
unexpected free variable with depth `^1.0` with outer binder ^0
stack backtrace:
   0: rust_begin_unwind
             at /rustc/595bc6f00369475047538fdae1ff8cea692ac385/library/std/src/panicking.rs:645:5
   1: core::panicking::panic_fmt
             at /rustc/595bc6f00369475047538fdae1ff8cea692ac385/library/core/src/panicking.rs:72:14
   2: <chalk_solve::infer::canonicalize::Canonicalizer<hir_ty::interner::Interner> as chalk_ir::fold::FallibleTypeFolder<hir_ty::interner::Interner>>::try_fold_free_var_ty
   3: <chalk_ir::Ty<hir_ty::interner::Interner> as chalk_ir::fold::TypeSuperFoldable<hir_ty::interner::Interner>>::super_fold_with
   4: <core::iter::adapters::GenericShunt<chalk_ir::cast::Casted<core::iter::adapters::map::Map<core::iter::adapters::cloned::Cloned<core::slice::iter::Iter<chalk_ir::GenericArg<hir_ty::interner::Interner>>>, <chalk_ir::Substitution<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with<core::convert::Infallible>::{closure#0}>, core::result::Result<chalk_ir::GenericArg<hir_ty::interner::Interner>, core::convert::Infallible>>, core::result::Result<core::convert::Infallible, core::convert::Infallible>> as core::iter::traits::iterator::Iterator>::next
   5: <chalk_ir::Substitution<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
   6: <chalk_ir::WhereClause<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
   7: <chalk_ir::DomainGoal<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
   8: <chalk_ir::Goal<hir_ty::interner::Interner> as chalk_ir::fold::TypeSuperFoldable<hir_ty::interner::Interner>>::super_fold_with
   9: <chalk_solve::infer::InferenceTable<hir_ty::interner::Interner>>::canonicalize::<chalk_ir::InEnvironment<chalk_ir::Goal<hir_ty::interner::Interner>>>
  10: <hir_ty::infer::unify::InferenceTable>::canonicalize::<chalk_ir::InEnvironment<chalk_ir::Goal<hir_ty::interner::Interner>>>
  11: <hir_ty::infer::unify::InferenceTable>::register_obligation_in_env
  12: <hir_ty::infer::unify::InferenceTable>::normalize_projection_ty
  13: <hir_ty::infer::unify::InferenceTable>::normalize_associated_types_in::<chalk_ir::Ty<hir_ty::interner::Interner>>::{closure#0}
  14: <hir_ty::fold_tys_and_consts::TyFolder<<hir_ty::infer::unify::InferenceTable>::normalize_associated_types_in<chalk_ir::Ty<hir_ty::interner::Interner>>::{closure#0}> as chalk_ir::fold::FallibleTypeFolder<hir_ty::interner::Interner>>::try_fold_ty
  15: <core::iter::adapters::GenericShunt<chalk_ir::cast::Casted<core::iter::adapters::map::Map<core::iter::adapters::cloned::Cloned<core::slice::iter::Iter<chalk_ir::GenericArg<hir_ty::interner::Interner>>>, <chalk_ir::Substitution<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with<core::convert::Infallible>::{closure#0}>, core::result::Result<chalk_ir::GenericArg<hir_ty::interner::Interner>, core::convert::Infallible>>, core::result::Result<core::convert::Infallible, core::convert::Infallible>> as core::iter::traits::iterator::Iterator>::next
  16: <chalk_ir::Substitution<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
  17: <chalk_ir::WhereClause<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
  18: <chalk_ir::QuantifiedWhereClauses<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
  19: <chalk_ir::DynTy<hir_ty::interner::Interner> as chalk_ir::fold::TypeFoldable<hir_ty::interner::Interner>>::try_fold_with::<core::convert::Infallible>
  20: <chalk_ir::Ty<hir_ty::interner::Interner> as chalk_ir::fold::TypeSuperFoldable<hir_ty::interner::Interner>>::super_fold_with
  21: <hir_ty::fold_tys_and_consts::TyFolder<<hir_ty::infer::unify::InferenceTable>::normalize_associated_types_in<chalk_ir::Ty<hir_ty::interner::Interner>>::{closure#0}> as chalk_ir::fold::FallibleTypeFolder<hir_ty::interner::Interner>>::try_fold_ty
  22: <chalk_ir::Ty<hir_ty::interner::Interner> as chalk_ir::fold::TypeSuperFoldable<hir_ty::interner::Interner>>::super_fold_with
  23: <hir_ty::infer::InferenceContext>::make_ty
  24: <hir_ty::infer::InferenceContext>::infer_expr_inner
  25: <hir_ty::infer::InferenceContext>::infer_expr_coerce
  26: <hir_ty::infer::InferenceContext>::infer_block
  27: <hir_ty::infer::InferenceContext>::infer_expr_inner
  28: <hir_ty::infer::InferenceContext>::infer_return
  29: hir_ty::infer::infer_query
  30: <salsa::derived::slot::Slot<hir_ty::db::InferQueryQuery, salsa::derived::AlwaysMemoizeValue>>::execute
  31: <_ as hir_ty::db::HirDatabase>::infer_query::__shim
  32: hir_ty::db::infer_wait
  33: <hir::semantics::SemanticsImpl>::analyze_impl
  34: <hir::semantics::SemanticsImpl>::resolve_path
  35: <ide_db::defs::NameRefClass>::classify
  36: ide::syntax_highlighting::highlight
  37: <ide::Analysis>::highlight_as_html
  38: <rust_analyzer::cli::flags::Highlight>::run
  39: rust_analyzer::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[matthiaskrgr]

smaller repro:

trait MapLookup<Q> {
    type MapValue;
}

trait Map: MapLookup<<Self as Map>::Key> {
    type Key;
}

fn main() {
    let _ = &() as &dyn Map<Key = u32, MapValue = u32>;
}