Allow type parameters on alias types

Author: owen-mc

go/extractor/extractor.go

@@ -475,12 +475,12 @@ func extractObjects(tw *trap.Writer, scope *types.Scope, scopeLabel trap.Label)
 				populateTypeParamParents(funcObj.Type().(*types.Signature).TypeParams(), obj)
 				populateTypeParamParents(funcObj.Type().(*types.Signature).RecvTypeParams(), obj)
 			}
-			// Populate type parameter parents for named types. Note that we
-			// skip type aliases as the original type should be the parent
-			// of any type parameters.
-			if typeNameObj, ok := obj.(*types.TypeName); ok && !typeNameObj.IsAlias() {
+			// Populate type parameter parents for named types.
+			if typeNameObj, ok := obj.(*types.TypeName); ok {
 				if tp, ok := typeNameObj.Type().(*types.Named); ok {
 					populateTypeParamParents(tp.TypeParams(), obj)
+				} else if tp, ok := typeNameObj.Type().(*types.Alias); ok {
+					populateTypeParamParents(tp.TypeParams(), obj)
 				}
 			}
 			extractObject(tw, obj, lbl)