Make sure private methods cannot be annotated (#377)

Author: slinkydeveloper

sdk-api-gen/src/main/java/dev/restate/sdk/gen/ElementConverter.java

@@ -162,6 +162,9 @@ private Handler fromExecutableElement(ServiceType serviceType, ExecutableElement
       messager.printMessage(
           Diagnostic.Kind.ERROR, "You cannot annotate a static init as Restate method");
     }
+    if (element.getModifiers().contains(Modifier.PRIVATE)) {
+      messager.printMessage(Diagnostic.Kind.ERROR, "The annotated method is private");
+    }
 
     boolean isAnnotatedWithShared = element.getAnnotation(Shared.class) != null;
     boolean isAnnotatedWithExclusive = element.getAnnotation(Exclusive.class) != null;

sdk-api-kotlin-gen/src/main/kotlin/dev/restate/sdk/kotlin/gen/KElementConverter.kt

@@ -135,6 +135,9 @@ class KElementConverter(
     if (function.functionKind != FunctionKind.MEMBER) {
       logger.error("Only member function declarations are supported as Restate handlers")
     }
+    if (function.getVisibility() == Visibility.PRIVATE) {
+      logger.error("The annotated function is private", function)
+    }
 
     val isAnnotatedWithShared =
         function.isAnnotationPresent(dev.restate.sdk.annotation.Shared::class)