I hacked together a small experiment in fully automating the documentation of a Swift codebase by asking GPT to add DocC comments. GPT does a pretty great job at it!
By pairing DoccGPT together with the Swift Package Index (which compiles and hosts your documentation for you) you can come very close to a fully self-documenting codebase. DoccGPT writes the markup for you, or at least takes an initial pass at it, and the Swift Package Index takes care of compiling and hosting the generated documentation for you.