Handle optional extra field in warn_unused_result (#863)

Fixes #861

Author: kroppt

ast/warn_unused_result_attr.go

@@ -10,7 +10,7 @@ type WarnUnusedResultAttr struct {
 }
 
 func parseWarnUnusedResultAttr(line string) *WarnUnusedResultAttr {
-	groups := groupsFromRegex(`<(?P<position>.*)>(?P<inherited> Inherited)?( warn_unused_result)?`, line)
+	groups := groupsFromRegex(`<(?P<position>.*)>(?P<inherited> Inherited)?( warn_unused_result)?( "")?`, line)
 
 	return &WarnUnusedResultAttr{
 		Addr:       ParseAddress(groups["address"]),

ast/warn_unused_result_attr_test.go

@@ -24,6 +24,12 @@ func TestWarnUnusedResultAttr(t *testing.T) {
 			Inherited:  true,
 			ChildNodes: []Node{},
 		},
+		`0x55c2df4f93b8 <col:53> warn_unused_result ""`: &WarnUnusedResultAttr{
+			Addr:       0x55c2df4f93b8,
+			Pos:        NewPositionFromString("col:53"),
+			Inherited:  false,
+			ChildNodes: []Node{},
+		},
 	}
 
 	runNodeTests(t, nodes)