The AssocOpaqueTy HIR node is not actually needed to differentiate from other hir nodes that were fed

compiler/rustc_ast_lowering/src/index.rs

@@ -55,7 +55,7 @@ pub(super) fn index_hir<'hir>(
         OwnerNode::TraitItem(item) => collector.visit_trait_item(item),
         OwnerNode::ImplItem(item) => collector.visit_impl_item(item),
         OwnerNode::ForeignItem(item) => collector.visit_foreign_item(item),
-        OwnerNode::AssocOpaqueTy(..) => unreachable!(),
+        OwnerNode::Synthetic => unreachable!(),
     };
 
     for (local_id, node) in collector.nodes.iter_enumerated() {