Update extractor to deal with 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)

go/ql/test/library-tests/semmle/go/Types/Aliases.expected

@@ -14,6 +14,11 @@ entities
 | aliases.go | aliases.go:22:6:22:6 | T | 1 | aliases.go:19:6:19:7 | S3 |
 | aliases.go | aliases.go:25:6:25:6 | H | 1 | file://:0:0:0:0 | signature type |
 | aliases.go | aliases.go:25:8:25:11 | Afs3 | 1 | aliases.go:19:6:19:7 | S3 |
+| aliases.go | aliases.go:29:6:29:9 | User | 1 | aliases.go:29:6:29:9 | User |
+| aliases.go | aliases.go:29:11:29:15 | UserT | 1 | file://:0:0:0:0 | type parameter type |
+| aliases.go | aliases.go:29:30:29:30 | x | 1 | file://:0:0:0:0 | type parameter type |
+| aliases.go | aliases.go:32:6:32:14 | UserAlias | 1 | aliases.go:29:6:29:9 | User |
+| aliases.go | aliases.go:32:16:32:25 | UserAliasT | 1 | file://:0:0:0:0 | type parameter type |
 #select
 | F | func(struct { x int }) int |
 | G | func(struct { x int }) int |