This is based off a post I made on the Swift forums. It concerns a NeverEmptyTrie type, along with a LinkedList support type, both of which are enumeration types with indirect cases.
The NeverEmptyTrie.doInsert seemed to have worked in its initial test cases. It was created in the middle of all the code I wrote. As I made test cases for later code in the library, the insertion tests started failing, with the payload having garbage values. There are several initializers that compose two tries together, but they haven't shown corruption in their tests (yet).