The attached project compiles fine on the command line but within Eclipse, the JPA metamodel generator produces wrong code.
In a fresh workspace with the latest JBoss Developer Studio plugin installed you have to configure Window > Preferences > Maven > Annotation Processing > Select Annotation Processing Mode => Automatically
When importing the project then, you are probably asked to install the Maven Connectors for
Maven Integration for Eclipse JDT APT
Install those and when all is done, make a Maven Update on the project to trigger the annotation processor(Right click on project > Maven > Update Project)
The code generated has errors because type variables are not properly resolved to their bounds but instead are rendered directly. I guess this is either a bug in Eclipse JDT, then this issue is for the JBoss Developer Studio team or a bug in the code generation of hibernate.
I tested some other JPA metamodel generators(OpenJPA, DataNucleus) too and only EclipseLink generated proper code within Eclipse!
JBoss Developer Studio Plugin 9.0.0.GA-v20151002-2235-B124