An enumeration should be able to be added to a set object (or any object for that matter but enums are the safest 1st level case).
So that syntax such as:
enum type --class ~.Regions
enum constant --name EUROPE
enum constant --name ASIA
enum constant --name NORTH_AMERICA
enum constant --name SOUTH_AMERICA
enum constant --name OCEANIA
entity --class ~.product
field set --fieldName supportedRegions --enum ~.Regions // clear & consistent
field set --fieldName supportedRegions --element ~.Regions // consistent
field other --fieldName supportedRegions --type java.util.Set --comment 'this would require the use to explicitly set the collection type (in this case ~.Regions)' // obvious single directionality but pain in the ass due to post editing of the generated code. (which is what this bug is trying to solve to begin with)
In these cases the generated field should be generated with the "@ElementCollection" annotation.
Also note that this could go beyond the realm of enums to basically any type but in the case of roo, enums are the safest, easiest and most common unsupported case (from my perspective).