The idl directory requires a CMakeLists.txt that must make the compilation of the CORBA IDL HELLO_Gen.idl file and install all the generated files into the correct module installation directories. This is done by using OMNIORB_ADD_MODULE() CMake macro:
The IDL file itself must define a CORBA component for which the name must be different from the module name to avoid name conflicts and define a CORBA interface that is derived at least from the EngineComponent interface of the Engines module. In case of HELLO module, the name of the CORBA component is HELLO_ORB and the name of the interface is HELLO_Gen.