Correctly consider depth when visiting WF goals

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -520,8 +520,9 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
         if let Some(ty::PredicateKind::AliasRelate(lhs, rhs, _)) = pred_kind.no_bound_vars() {
             if let Some(obligation) = goal
                 .infcx()
-                .visit_proof_tree(
+                .visit_proof_tree_at_depth(
                     goal.goal().with(goal.infcx().tcx, ty::ClauseKind::WellFormed(lhs.into())),
+                    goal.depth() + 1,
                     self,
                 )
                 .break_value()
@@ -529,8 +530,9 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                 return ControlFlow::Break(obligation);
             } else if let Some(obligation) = goal
                 .infcx()
-                .visit_proof_tree(
+                .visit_proof_tree_at_depth(
                     goal.goal().with(goal.infcx().tcx, ty::ClauseKind::WellFormed(rhs.into())),
+                    goal.depth() + 1,
                     self,
                 )
                 .break_value()

compiler/rustc_trait_selection/src/solve/inspect/analyse.rs

@@ -278,6 +278,10 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
         self.source
     }
 
+    pub fn depth(&self) -> usize {
+        self.depth
+    }
+
     fn candidates_recur(
         &'a self,
         candidates: &mut Vec<InspectCandidate<'a, 'tcx>>,
@@ -435,9 +439,18 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         goal: Goal<'tcx, ty::Predicate<'tcx>>,
         visitor: &mut V,
+    ) -> V::Result {
+        self.visit_proof_tree_at_depth(goal, 0, visitor)
+    }
+
+    fn visit_proof_tree_at_depth<V: ProofTreeVisitor<'tcx>>(
+        &self,
+        goal: Goal<'tcx, ty::Predicate<'tcx>>,
+        depth: usize,
+        visitor: &mut V,
     ) -> V::Result {
         let (_, proof_tree) = self.evaluate_root_goal(goal, GenerateProofTree::Yes);
         let proof_tree = proof_tree.unwrap();
-        visitor.visit_goal(&InspectGoal::new(self, 0, proof_tree, None, GoalSource::Misc))
+        visitor.visit_goal(&InspectGoal::new(self, depth, proof_tree, None, GoalSource::Misc))
     }
 }