Use json.RawMessage when polymorphic fields contain submessages (#88)

* Use json.RawMessage when polymorphic fields contain submessages

So far, these fields were represented as `interface{}`, which means that
the JSON library parsed these fields. However, they contain opaque data,
which makes it very inconvenient to work with such a message. Now,
fields with a submessage are represented as json.RawMessage, so that
applications can re-parse these submessages into the correct structure
more easily.

If the list of types only contains fundamental types, we stick with
`interface{}`.

Signed-off-by: Cornelius Weig <22861411+corneliusweig@users.noreply.github.com>

* Address review comments

Signed-off-by: Cornelius Weig <22861411+corneliusweig@users.noreply.github.com>

---------

Signed-off-by: Cornelius Weig <22861411+corneliusweig@users.noreply.github.com>

cmd/gentypes/gentypes.go

@@ -81,9 +81,9 @@ func parsePropertyType(propValue map[string]interface{}) string {
 		log.Fatal("property with no type or ref:", propValue)
 	}
 
-	switch propType.(type) {
+	switch typ := propType.(type) {
 	case string:
-		switch propType {
+		switch typ {
 		case "string":
 			return "string"
 		case "number":
@@ -124,10 +124,22 @@ func parsePropertyType(propValue map[string]interface{}) string {
 		}
 
 	case []interface{}:
+		// This field is polymorphic so it needs a generic type.
+		for _, el := range typ {
+			s, ok := el.(string)
+			if !ok {
+				log.Fatalf("property type contains a non-string of type %T: %#v", el, typ)
+			}
+			if s == "object" || s == "array" {
+				// It contains non-fundamental types, so treat it as opaque.
+				return "json.RawMessage"
+			}
+		}
+		// The possible types are all fundamental types, so we can use interface{}.
 		return "interface{}"
 
 	default:
-		log.Fatal("unknown property type", propType)
+		log.Fatalf("unknown property type %T (%#v)", typ, typ)
 	}
 
 	panic("unreachable")

codec_test.go

@@ -791,7 +791,7 @@ var exitedEventStruct = ExitedEvent{
 var terminatedEventString = `{"seq":5,"type":"event","event":"terminated","body":{"restart":true}}`
 var terminatedEventStruct = TerminatedEvent{
 	Event: *newEvent(5, "terminated"),
-	Body:  TerminatedEventBody{Restart: true},
+	Body:  TerminatedEventBody{Restart: json.RawMessage(`true`)},
 }
 
 var threadEventString = `{"seq":6,"type":"event","event":"thread","body":{"reason":"started","threadId":18}}`