fix NormalizesTo exception

Author: lcnr

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

@@ -67,6 +67,17 @@ impl<'a, 'tcx> InspectCandidate<'a, 'tcx> {
             }
 
             for &goal in &instantiated_goals {
+                // We need to be careful with `NormalizesTo` goals as the
+                // expected term has to be replaced with an unconstrained
+                // inference variable.
+                if let Some(kind) = goal.predicate.kind().no_bound_vars()
+                    && let ty::PredicateKind::NormalizesTo(_) = kind
+                {
+                    // FIXME: We currently skip these goals as
+                    // `fn evaluate_root_goal` ICEs if there are any
+                    // `NestedNormalizationGoals`.
+                    continue;
+                };
                 let (_, proof_tree) = infcx.evaluate_root_goal(goal, GenerateProofTree::Yes);
                 let proof_tree = proof_tree.unwrap();
                 try_visit!(visitor.visit_goal(&InspectGoal::new(
@@ -106,8 +117,7 @@ impl<'a, 'tcx> InspectCandidate<'a, 'tcx> {
                     // expected term has to be replaced with an unconstrained
                     // inference variable.
                     if let Some(kind) = goal.predicate.kind().no_bound_vars()
-                        && let ty::PredicateKind::NormalizesTo(predicate) = kind
-                        && !predicate.alias.is_opaque(infcx.tcx)
+                        && let ty::PredicateKind::NormalizesTo(_) = kind
                     {
                         // FIXME: We currently skip these goals as
                         // `fn evaluate_root_goal` ICEs if there are any