I think interactions between many types and functions would be harder to migrate, especially if you go so granular as to target individual types independently.

I think interactions between many types and functions would be harder to migrate, especially if you go so granular as to target individual types independently. Maybe if it was a migration from some checkpoint (timestamp / version / commit / whatever you like that describes an entire state of the code) to another, then you could migrate indirect code patterns that need to change as well. I think most of all one must have discipline to thoroughly think of old code and how it should behave now. I found that one can already do this by versioning code and types, similar to how an API endpoint might go from /v2/… to /v3/…. But again, it requires discipline and it’s not something I’d do for anything but very critical code.