What is your Eclipse version and what are you exacltly doing? Did you use a WildFly 13 RunTime?
I am using Wildfly 13 with IDE Eclipse Oxygen.3a, using Wildfly 12 server connector.
I am not using Wildfly 12 runtime on my maven project.
If I need some library from Wildfly 13 then I looked it at modules path and use it as a dependency provided on my project.