Revert "Auto merge of #79637 - spastorino:revert-trait-inheritance-self, r=Mark-Simulacrum"

This reverts commit b4def89d76, reversing
changes made to 7dc1e852d4.

compiler/rustc_infer/src/traits/util.rs

@@ -1,9 +1,10 @@
 use smallvec::smallvec;
 
 use crate::traits::{Obligation, ObligationCause, PredicateObligation};
-use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_middle::ty::outlives::Component;
 use rustc_middle::ty::{self, ToPredicate, TyCtxt, WithConstness};
+use rustc_span::symbol::Ident;
 
 pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -282,6 +283,37 @@ pub fn transitive_bounds<'tcx>(
     elaborate_trait_refs(tcx, bounds).filter_to_traits()
 }
 
+/// A specialized variant of `elaborate_trait_refs` that only elaborates trait references that may
+/// define the given associated type `assoc_name`. It uses the
+/// `super_predicates_that_define_assoc_type` query to avoid enumerating super-predicates that
+/// aren't related to `assoc_item`.  This is used when resolving types like `Self::Item` or
+/// `T::Item` and helps to avoid cycle errors (see e.g. #35237).
+pub fn transitive_bounds_that_define_assoc_type<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
+    assoc_name: Ident,
+) -> FxIndexSet<ty::PolyTraitRef<'tcx>> {
+    let mut stack: Vec<_> = bounds.collect();
+    let mut trait_refs = FxIndexSet::default();
+
+    while let Some(trait_ref) = stack.pop() {
+        if trait_refs.insert(trait_ref) {
+            let super_predicates =
+                tcx.super_predicates_that_define_assoc_type((trait_ref.def_id(), Some(assoc_name)));
+            for (super_predicate, _) in super_predicates.predicates {
+                let bound_predicate = super_predicate.bound_atom();
+                let subst_predicate = super_predicate
+                    .subst_supertrait(tcx, &bound_predicate.rebind(trait_ref.skip_binder()));
+                if let Some(binder) = subst_predicate.to_opt_poly_trait_ref() {
+                    stack.push(binder.value);
+                }
+            }
+        }
+    }
+
+    trait_refs
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // Other
 ///////////////////////////////////////////////////////////////////////////