Add comment to `Type` and `OpaqueTy` match

diff --git a/src/librustc/traits/specialize/specialization_graph.rs b/src/librustc/traits/specialize/specialization_graph.rs
index 0febdbe161d479276495568ab789121102b5c6a5..c64d6748ea97d563e47b7de484320192875c4415 100644 (file)
--- a/src/librustc/traits/specialize/specialization_graph.rs
+++ b/src/librustc/traits/specialize/specialization_graph.rs
@@ -436,7 +436,7 @@ pub fn item(
                 | (Const, Const)
                 | (Method, Method)
                 | (Type, Type)
-                | (Type, OpaqueTy)
+                | (Type, OpaqueTy)  // assoc. types can be made opaque in impls
                 => tcx.hygienic_eq(impl_item.ident, trait_item_name, trait_def_id),
 
                 | (Const, _)